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Vapor lock questions for the hotter climate guys

This is a discussion on Vapor lock questions for the hotter climate guys within the Carburetors (S30) forums, part of the 1st Generation Z (S30) category; The eastern seaboard is getting roasted lately, yesterday we hit 103 and I had parked the car in the sun ...


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    Default Vapor lock questions for the hotter climate guys

    The eastern seaboard is getting roasted lately, yesterday we hit 103 and I had parked the car in the sun after a spirited highway run. Like 15 min. later I got in started fine and off I went, I didn't make it a half a block when she started to go heavy lean so I ducked into a parking lot where it sputtered and died and I drifted into a shady spot and popped the hood.

    I got a gallon of water and cooled the carbs (twin su r/t's) fuel pump and hard lines. After a little coaxing I got her to start again and got myself to an air conditioned bar.

    Today its over 100 again, I did a short run to the gas station and the hardware store and back home. I parked in the sun for only 4 or 5 minutes, started it up and a half a block down the road it sputtered and stalled. I did the water trick and off I went. It seems to be that only when she's parked in the sun will she get hot enough to stall. It seems like opening the hood and splashing water on the fuel delivery components is enough to fix the vaporlock, so I'm not that concerned about it.

    My question to the desert dwellers is, how did you modify your cars to combat the vapor lock issues on your early carburated 240 Z? I did a search and read a bunch of stuff, but vapor lock is a hard search.

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    Typically, the daily temps reach over 100º every day from June to early October here in the SoCal desert. They're usually 110-115º this time of year. Even with the A/C on, I haven't experienced vapor lock with my '71 Z. The only mods on the car are a bigger radiator and aux electric fans that come on with the A/C.

    Prior to getting my current Porsche 914-6 which has carbs, I had a 914-4 with fuel injection that was easily vapor locked. A wet towel on the fuel lines helped with that car. Slow stop & go traffic on hot pavement was deadly - had to keep the air moving through the engine compartment.
    Dennis
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    These cars are know to have vapor lock problems. They came with asbestos insulation on the fuel rails. If yours is deterorated or missing the problem will be agrevated. One of the Datsun solutions starting in '72 or '73 was adding an electric fuel pump near the fuel tank to push the fuel against the vapor pressure. Perhaps you could add an electric fuel pump.

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    I've heard of carb guys recirculating their fuel. Maybe you could put a fuel pressure regulator right at your carbs, with a return flow line that feeds to your fuel/air separator (draining back into the tank). I don't know whether any of the lower pressure regulators are built that way (i.e. like the higher pressure EFI regulators).

    FAIW, my 280 will get a momentary vapor lock now after only a few min of sitting. This heat is brutal! I feel for you!
    Last edited by FastWoman; 07-23-2011 at 08:22 PM.
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    There should already be a fuel return circut. Do you have it functioning?

    Steve

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    Here are a couple of links for possible insulation sources:
    http://www.amazon.com/Corvette-Natur...518219&sr=1-10
    http://www.amazon.com/Natural-Protec...518219&sr=1-11
    I haven't measured the lengths of fuel line, but they might work, especially if they are wrapped in reflective tape.
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    The 240Z has a fuel return line. Make sure that it isn't plugged.

    With an electric fan, and an electric fuel pump I haven't had any problem with vapor lock, even at ZCON last July (When the temp was around 100). But my Z doesn't have air conditioning, so I don't drive it much when the temperature gets above 90F.
    '71 240Z, Because any fool can drive fast in a straight line.

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    We are running temps of 105 to 114 these days.My 810 runs fine EXCEPT when i park it for 15 to 20 minutes.Then i have a start issue as the fuel has become so hot it has pushed past the reg.FI cars don't vapor lock.

    Sarah,since you like tinkering,if you ran a momentary "on" switch to the fuel pump(or FP relay),you could over come this by turning the FP on with the switch.Datsun designed their FI cars to allow power to the fuel pump ONLY when the motor cranking or turning.

    Carb guys like the OP-insulate every line you can get your hands on under the hood.A functioning return system is mandatory.
    Another possiblility is the injector blower from the later 280 cars.
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    I already do that, ZTrain. I've got a switch wired in the console. I prime before every start. I have no trouble starting, but the engine runs a bit rough until I'm first able to take off down the street. Then everything is fine. Perhaps if I primed for longer... But as long as it starts, I'm fine.
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    Try priming for 30 seconds.If you can hear the FP,you SHOULD notice a change in pitch.

    On a related note,tomorrow i have some running around to do.I'm going to bring my IR thermometer with me just for ****s & giggles.
    Last edited by Z train; 07-24-2011 at 09:13 PM.
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    I recently went through the entire fuel circut and cleaned and blew everything out, including the returne lines. I Insulated the the lines using fiberglass matt insulation and reflective foil tape. It seemed to help a little bit, but Sunday the vapor lock happened again after sitting in the sun for 15 min. or so. I guess I will have to put the electric pusher pump back on the car.

    When I went with the round top carbs, I was told by many that it wasnt necessary to prevent the VL problem, so it was omitted, one less thing to fail. I guess that was wrong.

    I know there is a company called Pegasus racing that has the replacement fuel pump that was installed on the 73 recall, anyone use this pump? http://www.pegasusautoracing.com/pro...s.asp?RecID=85 This is the exact pump that was removed from my car, it has been internally modified since the original install to use less power and pump more efficently, but it is the faucet replacement.

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    If you are in the market for an electric pump you might look at the low pressure rx7 pump. I've got them on both of my 240's here in Texas and never had VL. They are very quiet and about $30 on eBay.
    Steve

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    Here we go again. FI cars can, and do vapor lock. It's the fuel that vaporizes. Fuel does not care if the car is carb or EFI, if fuel gets hot enough to exceed vapor pressure...it vaporizes. In a hose, a bucket, a tank, a fuel rail, or ANYWHERE.
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    The electric fan on the radiator with an adjustable cool down setting makes about as much sense as anything. Cars sitting heat sinking from the engine compartment plus what the sun's adding would benefit greatly, I'd think from a cooling fan on the radiator trying to get the cooling system cooled down to say 180 for 15 minutes blowing air thru the engine compartment whole you are in the hardware store. Your cooling system will think you are pampering it while in reality you are cooling down everything else..... too.
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    Bruce,here it's actually the heating radiating upwards off the asphalt that magnifies the heat.If i pop the hood and leave it sit on the safety catch,i have no issues restarting.

    THe wifes 620 is my only carbed vehicle.I have a functioning return system and NO insulation and i have zero vapor lock issues.
    Last edited by Z train; 07-25-2011 at 07:42 PM.
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    Quote Originally Posted by cygnusx1 View Post
    Here we go again. FI cars can, and do vapor lock. It's the fuel that vaporizes. Fuel does not care if the car is carb or EFI, if fuel gets hot enough to exceed vapor pressure...it vaporizes. In a hose, a bucket, a tank, a fuel rail, or ANYWHERE.
    Fuel injection runs at higher fuel pressure. Fuel and physics DO care about that. That increases the boiling point of the fuel. Also most FI have the pump either in or by the fuel tank. The pump itself never has to try to pump hot vaporized fuel. Also with the higher volume pumps that are run with EFI, if the fuel under the hood is vaporized the pump quickly displaces it with cooler liquid fuel. A properly functioning FI system is highly unlikely to vapor lock. If, while the vehicle is turned off, the system is bleeding off fuel pressure due to a faulty pump check valve, regulator, or injector then the system will be much more susceptible to vapor lock.

    Steve

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    Quote Originally Posted by Bruce Palmer View Post
    The electric fan on the radiator with an adjustable cool down setting makes about as much sense as anything. Cars sitting heat sinking from the engine compartment plus what the sun's adding would benefit greatly, I'd think from a cooling fan on the radiator trying to get the cooling system cooled down to say 180 for 15 minutes blowing air thru the engine compartment whole you are in the hardware store. Your cooling system will think you are pampering it while in reality you are cooling down everything else..... too.
    Bruce, you hit the nail on the head. Heat soak is the major component driving the problem. With the engine shut down the cooling system is no longer carrying away the heat from the engine. That's why cars have catch tanks on the cooling system. Coolant temps rise after shut down because that big hunk of cast iron and AL is HOT. A hot day, hot engine, no air flow, one can get vapor lock. Popping the hood induces air flow as the hottest air rises and escapes and cooler, relatively, air replaces it. Heat radiating from asphalt is not helping but is just one contributing factor.

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    Quote Originally Posted by doradox View Post
    Fuel injection runs at higher fuel pressure. Fuel and physics DO care about that. That increases the boiling point of the fuel. Also most FI have the pump either in or by the fuel tank. The pump itself never has to try to pump hot vaporized fuel. Also with the higher volume pumps that are run with EFI, if the fuel under the hood is vaporized the pump quickly displaces it with cooler liquid fuel. A properly functioning FI system is highly unlikely to vapor lock. If, while the vehicle is turned off, the system is bleeding off fuel pressure due to a faulty pump check valve, regulator, or injector then the system will be much more susceptible to vapor lock.

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    Yes less likely to. But they still can and do. Saying that they DO NOT vapor lock is FALSE, especially in our older systems. Why else would Nissan add the cooling snorkel in the latest evolutions? For the comfort and pleasure of the injection system?

    As a matter of fact, the hot fuel that sits INSIDE the bodies of the hot injectors WILL flash vaporize when the injectors are first fired, as the pressure drops to near atmosphere for the split second, each time the pintle fires. Yes, it happens that quickly, and affects how the FI car runs, until it clears up with cooler fuel. Note: Nissan pointed the blower snorkel at the injector bodies, not the rail.

    I have datalogged the effect and can offer hard evidence of this.

    Vapor lock in the rail of a 240Z is the same as the vapor lock in an injector of a 280Z. Just on a different scale.
    Last edited by cygnusx1; 07-26-2011 at 12:20 PM.
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    Quote Originally Posted by cygnusx1 View Post
    Yes less likely to. But they still can and do. Saying that they DO NOT vapor lock is FALSE, especially in our older systems. Why else would Nissan add the cooling snorkel in the latest evolutions? For the comfort and pleasure of the injection system?

    As a matter of fact, the hot fuel that sits INSIDE the bodies of the hot injectors WILL flash vaporize when the injectors are first fired, as the pressure drops to near atmosphere for the split second, each time the pintle fires. Yes, it happens that quickly, and affects how the FI car runs, until it clears up with cooler fuel. Note: Nissan pointed the blower snorkel at the injector bodies, not the rail.

    I have datalogged the effect and can offer hard evidence of this.

    Vapor lock in the rail of a 240Z is the same as the vapor lock in an injector of a 280Z. Just on a different scale.
    Really?Then explain why my Z engine(below) has NEVER "vaporlocked(for lack of a accurate word)

    But my daily driver 810 has warm start issues due to the fact that the check valve in the fuel pump is basically shot,thus letting pressure bleed off allowing the vapor to form.But the Z's system is perfect,thus no issues.
    Last edited by Z train; 07-26-2011 at 12:44 PM.
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    They don't all do it. It depends on how much heat transfers into the fuel rail and injectors. How do you know it's not happening? If you have a wideband O2, it can correct for it and you would never feel it. Nice engine bay BTW. Can you watch the EGO correction factors in a cold vs hot start? Is the hood vented? Oh yeah and you are the "merchant of cool!"
    Last edited by cygnusx1; 07-26-2011 at 12:56 PM.
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    Quote Originally Posted by cygnusx1 View Post
    1)They don't all do it. 2)It depends on how much heat transfers into the fuel rail and injectors. How do you know it's not happening? 3)If you have a wideband O2, it can correct for it and you would never feel it. 4)Nice engine bay BTW. Can you watch the EGO correction factors in a cold vs hot start?5) Is the hood vented? 6)Oh yeah and you are the "merchant of cool!"
    1)Right.The ones with MECHANICAL problems are the ones that do.
    2)Are you saying that the engine bay of my turbo stroker is COOLER than the factory issued 810?
    3)On cranking?
    4)Thanks.
    5)Neither hood is vented.
    6)Yes,Yes- i am.
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    Quote Originally Posted by Z train View Post
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    It was bound to happen sooner or later.

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    Right, because yours does not vapor lock, no cars with FI do? Read the FSM. What is the allowable decay time for the factory fuel pressure after shutdown?
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    Time to play with trains.See ya Thursday-ish.
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    Quote Originally Posted by cygnusx1 View Post
    Right, because yours does not vapor lock, no cars with FI do? Read the FSM. What is the allowable decay time for the factory fuel pressure after shutdown?
    I was doing a little light reading and found this little tidbit in the 76 FSM.

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    Yes, then why did Nissan have to add hood vents, and then add a blower, that takes cooler air from under the passengers side frame rail, and blows it directly onto the injector bodies, for a period of time, after the engine is shut off? Clearly, the EFI Z cars had issues with heat and fuel injection. What was that issue? Safe bet that they were battling vapor lock in the injector bodies. I see it all the time, even in a perfectly functioning EFI system. Newer injection systems are designed much differently than the L-Jet, so that the vaporizing fuel inside the injector issue is even more rare.

    Saying that a fuel injected Z won't vapor lock is false. Shouldn't vapor lock, is more accurate. How many EFI Z owners have had hard starting after parking hot for 10-15 minutes? Especially the early models without vented hoods. My 76 did this occasionally when it was bone stock, and was in perfect working order. Fuel types/brands might also play a small part in why peoples experiences differ.
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    Quote Originally Posted by cygnusx1 View Post
    Yes, then why did Nissan have to add hood vents, and then add a blower, that takes cooler air from under the passengers side frame rail, and blows it directly onto the injector bodies, for a period of time, after the engine is shut off? Clearly, the EFI Z cars had issues with heat and fuel injection. What was that issue? Safe bet that they were battling vapor lock in the injector bodies. I see it all the time, even in a perfectly functioning EFI system. Newer injection systems are designed much differently than the L-Jet, so that the vaporizing fuel inside the injector issue is even more rare.

    Saying that a fuel injected Z won't vapor lock is false. Shouldn't vapor lock, is more accurate. How many EFI Z owners have had hard starting after parking hot for 10-15 minutes? Especially the early models without vented hoods. My 76 did this occasionally when it was bone stock, and was in perfect working order. Fuel types/brands might also play a small part in why peoples experiences differ.
    I'm not the one saying it never happens. You said read the FSM. So I did. Be careful what you ask for. You just might get it.

    Steve

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    Well, there is scientific proof then. I must be wrong.
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    FAIW, I understand that ethanol gas has a higher vapor pressure than genuine 1970's gas, so it's more prone to vapor locking. Furthermore, gasoline blends are varied seasonally with more volatiles during the winter. When these mixes are not conscientiously managed by the gasoline suppliers, you can get almost anything from the pump -- even gas blended for cooler climates with up to 30% ethanol. I suspect that's why some people have vapor lock problems and others don't. Where I live, most gas is @#$%.
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    Quote Originally Posted by cygnusx1 View Post
    Well, there is scientific proof then. I must be wrong.
    I didn't say you were wrong. Other sources are saying that.
    I said "A properly functioning FI system is highly unlikely to vapor lock.'
    I spent 20 years as an auto tech in Tucson and never saw or heard of an injected Z vapor locking. My 75 never did it. Apparently you have some trouble.

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    Quote Originally Posted by Z train View Post
    Bruce,here it's actually the heating radiating upwards off the asphalt that magnifies the heat.If i pop the hood and leave it sit on the safety catch,i have no issues restarting.

    THe wifes 620 is my only carbed vehicle.I have a functioning return system and NO insulation and i have zero vapor lock issues.
    Me thinks that were I to live where the pavement temps got high enough to cause vapor lock, I'd be searching for a new location. nyuck nyuck

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    Been working on EFI Datsun's myself for over 25 years. I see vapor lock issues, even when the system holds pressure. It very well could be the fuel formula we get here in the Northeast.
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    Quote Originally Posted by doradox View Post
    I didn't say you were wrong. Other sources are saying that.
    I said "A properly functioning FI system is highly unlikely to vapor lock.'
    I spent 20 years as an auto tech in Tucson and never saw or heard of an injected Z vapor locking. My 75 never did it. Apparently you have some trouble.

    Steve
    The confusion here is in the semantics between true 'vapor lock' and 'vapor lock type symptoms'. In the combined 18 years of the 'joy of ownership' of mid to late 70s Datsun EFI vehicles the only time I ever experienced that was when the check valve went bad on my 810. Replaced it - no further problems. It gets well over 100 degrees everywhere I've lived here in those 18 years. If it happens on a carbed car it's vapor lock if it happens on an EFI car is a mechanical problem that manifests itself with vapor lock type symptoms. When everything is right, it will never happen. That can't be said of carbed cars. Even with wrapped fuel lines the fuel pressure is only, what, 3-5 psi.?
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    I will repeat. Fuel that sits under pressure, behind the injector pintle, becomes superheated. Superheated is a technical term. What happens to superheated liquids when a catalyst is introduced or the pressure is suddenly reduced? It flash vaporizes. This DOES happen inside of the injectors when the pintles are fired from a superheated state. Nissan, not me, installed a cooling arrangement in an effort to keep the injector bodies from becoming holding chambers for superheated fuel. Again, not my idea, it was the idea of Nissan engineers. The flash vaporization on hot start, can also happen in the fuel rail as the pressure sine waves bottom out, as the BATCH injectors all fire at once. The fuel damper is too far away to absorb this wave fully. Sequential injectors minimizes the amplitude of the sine pressure waves in the fuel rail, which can prevent this effect from creeping into the rail. When it happens, you have a situation where you are injecting vapor into the combustion chamber. Vapor will not burn. Thus it's a sort of vapor lock. Call it what you will. Yes, it is probably fuel dependent.

    Now, can anyone answer why the cooling fan for the injectors was added?
    Last edited by cygnusx1; 07-27-2011 at 07:54 AM.
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    Alot of what I've seen makes it unclear as to whether it was for emissions purposes or for the reason you say. Can anyone answer why it was only used on the 280ZX and not the 79-83 810/910 Maxima or any of the 4 cyl EFI Datsun/Nissans of the era? You can 'repeat' as many times as you want. I know what vapor lock is. Fuel could well be a factor. Never ran any of them on ethanol. All we can do is conjecture and agree to disagree.....
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    Quote Originally Posted by sblake01 View Post
    The confusion here is in the semantics between true 'vapor lock' and 'vapor lock type symptoms'. In the combined 18 years of the 'joy of ownership' of mid to late 70s Datsun EFI vehicles the only time I ever experienced that was when the check valve went bad on my 810. Replaced it - no further problems. It gets well over 100 degrees everywhere I've lived here in those 18 years. If it happens on a carbed car it's vapor lock if it happens on an EFI car is a mechanical problem that manifests itself with vapor lock type symptoms. When everything is right, it will never happen. That can't be said of carbed cars. Even with wrapped fuel lines the fuel pressure is only, what, 3-5 psi.?
    I would tend to agree with you.

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    Quote Originally Posted by cygnusx1 View Post
    I will repeat. Fuel that sits under pressure, behind the injector pintle, becomes superheated. Superheated is a technical term. What happens to superheated liquids when a catalyst is introduced or the pressure is suddenly reduced? It flash vaporizes. This DOES happen inside of the injectors when the pintles are fired from a superheated state. Nissan, not me, installed a cooling arrangement in an effort to keep the injector bodies from becoming holding chambers for superheated fuel. Again, not my idea, it was the idea of Nissan engineers. The flash vaporization on hot start, can also happen in the fuel rail as the pressure sine waves bottom out, as the BATCH injectors all fire at once. The fuel damper is too far away to absorb this wave fully. Sequential injectors minimizes the amplitude of the sine pressure waves in the fuel rail, which can prevent this effect from creeping into the rail. When it happens, you have a situation where you are injecting vapor into the combustion chamber. Vapor will not burn. Thus it's a sort of vapor lock. Call it what you will. Yes, it is probably fuel dependent.

    Now, can anyone answer why the cooling fan for the injectors was added?
    Do have a source for your assertion that vapor will not burn? I was under the impression that fuel needed to vaporize into air in order for combustion to take place. Something about the fuel molecules needing to be distributed among the O2 molecules so the oxidation reaction (burn) can take place. Maybe vapor isn't the technical term you were looking for.

    Steve

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    Quote Originally Posted by cygnusx1 View Post
    Been working on EFI Datsun's myself for over 25 years. I see vapor lock issues, even when the system holds pressure. It very well could be the fuel formula we get here in the Northeast.
    So you are or were an auto tech?

    Steve

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    Mech. Engineer but it's irrelevant. Fuel has to atomize to burn. Not vaporize (it's about droplet size). Vapor would require a different condition to ignite than present in the IC engine. I am thinking that the key to the differing experience has to do with A)Regional fuel quality and B)Condition and rate of pressure drop of the sealed system of Northeast vs Cars in warmer climates.

    I am not sure if cars in the warmer climates experience this, but in cold weather, the hoses in the Z's EFI tend to leak. There is actually a recall or service bulletin for the issue. It may be that the cars exposed to colder climates, do not hold pressure long enough or high enough to ward off vapor-lock, unless the owner has taken remedial actions. That's why I asked about what the spec in the manual is for holding system pressure, in case you wondered. I can't seem to find it anywhere. I know it's not indefinite though. The "cold weather fuel line leaking", is not isolated to Datsuns either. Later model Subarus also had a similar recall, last year.
    Last edited by cygnusx1; 07-27-2011 at 12:17 PM.
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    I am going to research the chemistry/physics of fuel atomization vs vaporization and the effects on combustion, but I know the short of it. Fuel injectors are not good vapor injectors.
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    Quote Originally Posted by cygnusx1 View Post
    I am going to research the chemistry/physics of fuel atomization vs vaporization and the effects on combustion, but I know the short of it. Fuel injectors are not good vapor injectors.
    Being designed for liquid fuel I don't imagine they are.
    FWIW I'm a BSME Purdue. Sold the shop, moved to the midwest, went back to school.
    Any chance the difference in volume of gas vapor vs. liquid is causing trouble?
    Steve
    Last edited by doradox; 07-27-2011 at 02:52 PM.

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    I did a little digging into the vapor pressure of gasoline and learned that the petroleum industry and US government have standardized on the "Reid Vapor Pressure (RVP)" test. It specifies a test temperature of 100C and measures the resultant vapor pressure in psi.

    The vapor pressure is constrained by government regulations and is tightly controlled by industry. The limits change by location and time of year, but from what I found, the vapor pressure of your typical pump gas (at the RVP test temperature of 100 degrees C) is between 5 psi and 11 psi depending on where you live and what season it is.

    Vapor pressure will decrease as temp goes down and go higher as the temp increases.

    So how hot do the fuel get and what pressure is it under?

    Being as how I'm not an ME, it's probably not a good idea to wade into the middle between two of them, but I've never been very bright...

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    Quote Originally Posted by cygnusx1 View Post
    I am going to research the chemistry/physics of fuel atomization vs vaporization and the effects on combustion, but I know the short of it. Fuel injectors are not good vapor injectors.
    I was thinking about what you said. "Fuel injectors are not good vapor injectors"
    Is it possible they simply are unable to flow enough vapor to get the mixture rich enough to ignite? Gas volume vs. liquid volume is very roughly 800 to 1. That would be a lot of vapor to pass through the injector nozzle.

    Steve

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    I have been looking for something to wrap my fuel lines in. I cant really find anything that looks alright and will get the job done. can anyone link me to a product they know of that will work?
    Thanks guys

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    Quote Originally Posted by Captain Obvious View Post
    I did a little digging into the vapor pressure of gasoline and learned that the petroleum industry and US government have standardized on the "Reid Vapor Pressure (RVP)" test. It specifies a test temperature of 100C and measures the resultant vapor pressure in psi.

    The vapor pressure is constrained by government regulations and is tightly controlled by industry. The limits change by location and time of year, but from what I found, the vapor pressure of your typical pump gas (at the RVP test temperature of 100 degrees C) is between 5 psi and 11 psi depending on where you live and what season it is.

    Vapor pressure will decrease as temp goes down and go higher as the temp increases.

    So how hot do the fuel get and what pressure is it under?

    Being as how I'm not an ME, it's probably not a good idea to wade into the middle between two of them, but I've never been very bright...
    Haha don't worry, I my engineering degree is mostly evidenced by the grease under my fingernails. I am no threat for sure. I am only a threat to myself. Good data that you found. Funny, I just got off the phone with a good friend of mine who is also an engineer, and worked on fuel systems for snowmobiles, now he is with NASA, and he gave me almost the same info you just did. He said that typical cold region Winter fuels can definitely vaporize in Summer conditions found in a fuel injection system. And he confirmed that fuel vapor is a completely different phase than atomized fuel. Fuel vapor is much closer to air than it is to fuel. He also said that it is possible to have a "geyser" effect. When the injector opens, the superheated fuel can instantly vaporize and apply back pressure to keep liquid fuel from entering the stream.
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    Quote Originally Posted by Captain Obvious View Post
    The vapor pressure is constrained by government regulations and is tightly controlled by industry.
    Controlled? Yes.

    Tightly (or well)? I very seriously doubt it.

    Remember, you can buy up to 30% ethanol gas at the pump, even when 10% is the maximum allowed by law. There's definitely a control problem, and the mechanics in my area have their hands full, trying to fix the consequences.
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    Quote Originally Posted by FastWoman View Post
    Controlled? Yes.

    Tightly (or well)? I very seriously doubt it.
    Yeah, You're right. I probably should have said "the upper limit on vapor pressure is supposed to be tightly controlled"

    Research indicates that the intention of the gov't is to reduce the amount of fuel evaporation into the atmosphere as much as possible while still allowing the fuel to work well in application. The way they do this is to dictate an upper limit on the vapor pressure for different locations at different times of the year. How the manufacturers achieve that vapor pressure limit seems to be mostly up to them, including the composition and ethanol content of the fuel.

    My research turned up two things that always seem to be true:

    1) Winter fuel (RFG) is allowed to have a higher vapor pressure than summer fuel, and...
    2) California requires a lower vapor pressure than most other states.

    Quote Originally Posted by cygnusx1 View Post
    And he confirmed that fuel vapor is a completely different phase than atomized fuel. Fuel vapor is much closer to air than it is to fuel.
    Of course they are. You remember the difference between "suspensions" and "solutions", don't you?

    And you mentioned the concept of superheat earlier and I forgot to ask... Why do you think the fuel in the injectors is superheated? Seems difficult to achieve.



    Have we strayed far enough from the OP's question yet?

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    Technically, it's not superheated the whole time, because the rail pressure keeps it in a liquid phase even though it's above it's STP boiling point. However it passes through a superheated state just before flashing, as the pressure in the injector column drops upon firing.

    In fact, the snap action "shock" of the pintle opening might be enough of a catalyst to start the boil.
    Last edited by cygnusx1; 07-28-2011 at 08:15 AM.
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    Quote Originally Posted by cygnusx1 View Post
    . Fuel has to atomize to burn. Not vaporize (it's about droplet size). Vapor would require a different condition to ignite than present in the IC engine.
    Atomization helps bring about vaporization which is what fuel needs to burn. Read the conclusions on page 4 and 5 of this document.
    http://nepis.epa.gov/Exe/ZyNET.exe/91002JP9.txt?ZyActionD=ZyDocument&Client=EPA&Index=Prior%20to%201976&Docs=&Query=APTD0964%20or%20fuel%20or%20atomization%20an d%20vapor&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=pubnumber^%22APTD0964%22&QFieldYear=&QFieldMonth=&QFieldDay=&UseQField=pubnumber&IntQFieldOp=1&ExtQFieldOp=1&XmlQuery=&File=D%3A\ZYFILES\INDEX%20DATA\70THRU75\TXT\000000 07\91002JP9.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h|-&MaximumDocuments=10&FuzzyDegree=0&ImageQuality=r105g16/r105g16/x150y150g16/i600&Display=p|f&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=-1&ZyEntry=5
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    Absolutely. However if the fuel injector injects a teaspoon of droplets, perse, vs a teaspoon of vapor, you have a totally different atom count. X-TAU is all about fuel depositing and vaporizing AFTER the injector. I has to come out of the injector as a mist of fuel droplets.

    You link does not work, but I think I am familiar with that document.

    I have used silicone tubing sliced lengthwise, and slipped over the injector bodies, and the fuel lines as insulation. However it didn't work too well. I don't think silicone was the right choice. It needs to be less thermally conductive and maybe even reflective. There are products designed to do just this. Search summit and jegs for heat control products for an easy idea.
    Last edited by cygnusx1; 07-28-2011 at 10:41 AM.
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    Try this link. The original one is so long that it would be almost impossible to properly parse it for use as a website link.
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    That is pretty much some of the basis of the CVCC from Honda, I think. The problem see with vapor in the injectors is simply from the fact that if the injector fires for 2.5ms to atomize liquid fuel, you get X amount of fuel in the chamber. If it opens up for 2.5ms and the fuel vaporizes through the nozzle path you are getting MUCH less than X amount of fuel to the chamber. This all clears up once fresh cool fuel makes it down to the pintles. Usually it takes about 30 seconds or so, once the engine fires, in my experience with the stock EFI. Now my car is a different story. It's not stock, it generates a ton of heat, no hood vents, and the billet rail does a great job of transferring heat into the fuel. With the car shut down hot, even with 30-40 psi still on the gauge, the fuel in the injectors exceeds the boiling point at atmospheric P. Even if I let it idle on a hot day the mixture will begin to lean out as the pulsewidth of the injector remains steady. The fuel rail is recirculated and I have two pulse dampers in the loop. My injectors are Bosch 440cc so they are at a pretty low duty cycle at idle which might explain why they can't cool themselves off with fuel. Perhaps?

    The energy of one gallon of gasoline is roughly 112,000 BTU
    A fully evaporated (vaporized) gallon of fuel occupies about 160 gallons.
    Therefore, one gallon of gasoline vapor contains only 700 BTU.

    You would need to inject 160 times the volume of vapor as you did liquid to get the cylinder fired off properly. So, if there is nothing but vapor in the injector OR the fuel is vaporizing coming through the nozzle, and the liquid phase fuel is not flowing through fully, you will be very lean.
    Last edited by cygnusx1; 07-28-2011 at 01:26 PM.
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    I did a little experiment today. I had run an errand and parked my car in the shade. I didn't get the engine very hot at all, but I suppose it was hot enough. When I restarted after only a couple of minutes of sitting (literally), I had such a rough start that the engine died. Before turning the key again, I thought I'd try ZTrain's suggestion of holding my fuel pump priming switch for quite a long time. I let the pump run for maybe 1-2 min, and.... STILL A ROUGH START.

    I must have done a pretty thorough job of flushing fuel vapor from the rail and replacing it with cool fuel, but still no-go. I now suspect the injectors get hot enough to vaporize, fuel, which bubbles, rises and condenses in the fuel rail, while new bubbles form. Then when I start the engine, I have to inject small vapor pockets for a short while until the injectors are cooled by the incoming fuel, and until the intake manifold is cooled by the fresh air rushing through.

    If that's the case, I suspect there's no amount of insulating that could be done to completely resolve the problem.

    And again, I suspect this could relate to the formulation of gasoline -- luck of the pump, as it were. I'm having more problems with this last batch of gas than I usually do. I got it at a station that's not my usual place.

    I wonder whether I would be able to hear the fuel boil if I put a stethoscope to the injector after engine shutoff. Unfortunately I don't have a mechanic's stethoscope. Next time I'm at HF...
    Last edited by FastWoman; 07-28-2011 at 01:52 PM.
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    Quote Originally Posted by cygnusx1 View Post
    That is pretty much some of the basis of the CVCC from Honda, I think. The problem see with vapor in the injectors is simply from the fact that if the injector fires for 2.5ms to atomize liquid fuel, you get X amount of fuel in the chamber. If it opens up for 2.5ms and the fuel vaporizes through the nozzle path you are getting MUCH less than X amount of fuel to the chamber. This all clears up once fresh cool fuel makes it down to the pintles. Usually it takes about 30 seconds or so, once the engine fires, in my experience with the stock EFI. Now my car is a different story. It's not stock, it generates a ton of heat, no hood vents, and the billet rail does a great job of transferring heat into the fuel. With the car shut down hot, even with 30-40 psi still on the gauge, the fuel in the injectors exceeds the boiling point at atmospheric P. Even if I let it idle on a hot day the mixture will begin to lean out as the pulsewidth of the injector remains steady. The fuel rail is recirculated and I have two pulse dampers in the loop. My injectors are Bosch 440cc so they are at a pretty low duty cycle at idle which might explain why they can't cool themselves off with fuel. Perhaps?

    The energy of one gallon of gasoline is roughly 112,000 BTU
    A fully evaporated (vaporized) gallon of fuel occupies about 160 gallons.
    Therefore, one gallon of gasoline vapor contains only 700 BTU.

    You would need to inject 160 times the volume of vapor as you did liquid to get the cylinder fired off properly. So, if there is nothing but vapor in the injector OR the fuel is vaporizing coming through the nozzle, and the liquid phase fuel is not flowing through fully, you will be very lean.
    So what I said about vaporized fuel being required for combustion as opposed to not combusting as you had proposed was correct. And my thoughts questioning the injector's capacity to flow the volume of vapor required to support combustion were on track. What you are saying makes more sense now that we have generated a hypothesis that makes physical sense. Interesting.

    Steve

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    Has anyone read the owners manual for the 280z (I know it's in the '75) about starting the car after the engine has been running and the car has only sat for a short time? I was surprised to see that it instructed one to press the gas pedal all the way on to restart. I expect this is to flush out the injector/fuel rail.
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    Quote Originally Posted by sblake01 View Post
    Try this link. The original one is so long that it would be almost impossible to properly parse it for use as a website link.
    Thanks. Much better.

    Steve

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    Quote Originally Posted by doradox View Post
    I was doing a little light reading and found this little tidbit in the 76 FSM.

    Click image for larger version. 

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    Quote Originally Posted by cygnusx1 View Post
    Technically, it's not superheated the whole time, because the rail pressure keeps it in a liquid phase even though it's above it's STP boiling point. However it passes through a superheated state just before flashing, as the pressure in the injector column drops upon firing.

    In fact, the snap action "shock" of the pintle opening might be enough of a catalyst to start the boil.
    STP has nothing to do with this. It's all about vapor pressure at elevated temps. You're nowhere near STP.

    Also, your use of the term "superheated" has become is a little confusing to me, so it might be prudent to make sure we're talking the same thing...

    What's your understanding of "superheated"?

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    Just make sure your system is holding pressure after you turn off the car. That is usually the first thing to eliminate when faced with this issue. How long it should hold pressure? I can't find that number anywhere so in my logical opinion, "long enough for the engine to cool down a bit" ;-) If you do hold pressure, then you are seeing exactly what I am talking about...assuming of course all other components of the EFI check out...and it's a pretty long list. I like to compare specs to the FSM right from the ECU connector where you have access to all FI components. Of course theres more stuff that needs to be checked out. It's so easy to say something else is causing the issue, and it CAN'T happen, but I know that this CAN happen due to a vaporizing fuel issue.
    Last edited by cygnusx1; 07-28-2011 at 02:09 PM.
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    Quote Originally Posted by cygnusx1 View Post
    I see vapor lock issues, even when the system holds pressure.
    This is flat physically IMPOSSIBLE.

    The check valve on my 810 is failing.I know this.It has starting issues.My turbo car (which runs even hotter)has no failing parts and it has no issues.
    __________________________________________________ __________________________________________________ ______
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    The confusion here is in the semantics between true 'vapor lock' and 'vapor lock type symptoms'. In the combined 18 years of the 'joy of ownership' of mid to late 70s Datsun EFI vehicles the only time I ever experienced that was when the check valve went bad on my 810. Replaced it - no further problems. It gets well over 100 degrees everywhere I've lived here in those 18 years. If it happens on a carbed car it's vapor lock if it happens on an EFI car is a mechanical problem that manifests itself with vapor lock type symptoms. When everything is right, it will never happen. That can't be said of carbed cars. Even with wrapped fuel lines the fuel pressure is only, what, 3-5 psi.?



    Mirrors my experiences with the exception of the wifes truck (78 620 2.3 stroker)having a DGV Weber with a return line and zero vapor lock issues.
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    Quote Originally Posted by cygnusx1 View Post
    Just make sure your system is holding pressure after you turn off the car. That is usually the first thing to eliminate when faced with this issue. How long it should hold pressure? I can't find that number anywhere so in my logical opinion, "long enough for the engine to cool down a bit" ;-) If you do hold pressure, then you are seeing exactly what I am talking about...assuming of course all other components of the EFI check out...and it's a pretty long list. I like to compare specs to the FSM right from the ECU connector where you have access to all FI components. Of course theres more stuff that needs to be checked out. It's so easy to say something else is causing the issue, and it CAN'T happen, but I know that this CAN happen due to a vaporizing fuel issue.
    My second 810(not running at the moment) held fuel pressure(down to 10 pounds) for FOUR MONTHS before i cracked open the line.I'd say the check valve is fine.
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    Quote Originally Posted by Z train View Post
    This is flat physically IMPOSSIBLE.

    The check valve on my 810 is failing.I know this.It has starting issues.My turbo car (which runs even hotter)has no failing parts and it has no issues.
    __________________________________________________ __________________________________________________ ______
    By Mr.Blake:
    The confusion here is in the semantics between true 'vapor lock' and 'vapor lock type symptoms'. In the combined 18 years of the 'joy of ownership' of mid to late 70s Datsun EFI vehicles the only time I ever experienced that was when the check valve went bad on my 810. Replaced it - no further problems. It gets well over 100 degrees everywhere I've lived here in those 18 years. If it happens on a carbed car it's vapor lock if it happens on an EFI car is a mechanical problem that manifests itself with vapor lock type symptoms. When everything is right, it will never happen. That can't be said of carbed cars. Even with wrapped fuel lines the fuel pressure is only, what, 3-5 psi.?



    Mirrors my experiences with the exception of the wifes truck (78 620 2.3 stroker)having a DGV Weber with a return line and zero vapor lock issues.

    OK we get it, none of your vehicles exhibit this behavior. Does not make it impossible. Try to open your mind and envision vapor lock inside the injector when they initially fire, on a micro scale. If you can't understand this or don't want to call it vapor lock then say so, or call it what you will. At this point it's a theory, that others besides me also have. Maybe it's not fuel vaporizing. Maybe heat effects the injection in some other way. Can you offer any explanations?

    Some more reading:
    http://www.crxsi.com/info/fuel-relat...on-Systems.htm
    Last edited by cygnusx1; 07-28-2011 at 05:56 PM.
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    Quote Originally Posted by cygnusx1 View Post
    This all clears up once fresh cool fuel makes it down to the pintles. Usually it takes about 30 seconds or so, once the engine fires, in my experience with the stock EFI. Now my car is a different story. It's not stock, it generates a ton of heat, no hood vents, and the billet rail does a great job of transferring heat into the fuel. With the car shut down hot, even with 30-40 psi still on the gauge, the fuel in the injectors exceeds the boiling point at atmospheric P.
    You think you're boiling fuel even with a 30 psi rail?

    So where exactly is it that you think the fuel boils? And do you think it's boiling a little at a time on each injector pulse and blowing only vapor into the manifold, or do you think it's sustained and bubbling back into the rail as FastWoman described?

    One thing that's completely clear from all of this discussion is that with my carbureted Z, I'm simply screwed...

    And not that it really matters, but I'm still unclear on why you're bringing the concept of superheating into this... You really don't even need it to support the beliefs under discussion. But in any event, it doesn't detract, it's just probably unnecessary.

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    Here is my theory. I think the fuel is sitting in the heat soaking injectors and rail, with a vapor pressure of, say, 10psi. Note: it's not a vapor yet because it's safely compressed in the system at 30psi. Say the rail and injectors reach 190 degrees F in heat soak. You turn the key. When the injector opens BAM. In slow motion. The injectors pressure drops suddenly and dramatically, as one end of it is exposed to either atmospheric pressure or engine vacuum. The rail pressure drops too. The system then recovers pressure as the injectors close and the pressure restores. So lets take an instantaneous look. The injector is open. The pressure at the pintle exit is "manifold vacuum". The pressure in the fuel feed lines is 34psi. What you have is a gradient of pressure tapering from 34psi down to vacuum. Somewhere in that gradient path, from fuel pump to pintle, there is a point, eg. 10psi, where the superheated fuel will vaporize. That point could be in the injector body, the hoses, or the rail. You end up with vapor pockets. Now for a few seconds, or minutes, you have vapor passing intermittently through the injectors. OK They are not locked. SO maybe it's not technically vapor lock. One thing is for sure. With Winter or marginal suburban fuels, and higher elevations, with approaching 200 degree-F injector bodies, the conditions are right for flash vaporization.

    Why do I call it superheated?
    http://en.wikipedia.org/wiki/Geyser

    Read the section about ERUPTIONS. It's the same effect. Transparent fuel rails anyone! I bet Nissan has a few in the engineering R&D archives. Why the injector cooling fan in the ZX? Still no answers. Do I hear crickets?

    For carbs, you can build heat sheilds, try other fuel brands, pop the hood, insulate the lines...all the same thing EFI cars can do really.


    newsflash...do I see posts from VERY knowledgable people about EFI cars vapor locking?

    http://forums.hybridz.org/index.php/...58#entry949958
    Last edited by cygnusx1; 07-28-2011 at 09:39 PM.
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    Quote Originally Posted by cygnusx1 View Post
    Here is my theory. I think the fuel is sitting in the heat soaking injectors and rail, with a vapor pressure of, say, 10psi. Note: it's not a vapor yet because it's safely compressed in the system at 30psi. Say the rail and injectors reach 190 degrees F in heat soak. You turn the key. When the injector opens BAM. In slow motion. The injectors pressure drops suddenly and dramatically, as one end of it is exposed to either atmospheric pressure or engine vacuum. The rail pressure drops too. The system then recovers pressure as the injectors close and the pressure restores. So lets take an instantaneous look. The injector is open. The pressure at the pintle exit is "manifold vacuum". The pressure in the fuel feed lines is 34psi. What you have is a gradient of pressure tapering from 34psi down to vacuum. Somewhere in that gradient path, from fuel pump to pintle, there is a point, eg. 10psi, where the superheated fuel will vaporize. That point could be in the injector body, the hoses, or the rail. You end up with vapor pockets. Now for a few seconds, or minutes, you have vapor passing intermittently through the injectors. OK They are not locked. SO maybe it's not technically vapor lock. One thing is for sure. With Winter or marginal suburban fuels, and higher elevations, with approaching 200 degree-F injector bodies, the conditions are right for flash vaporization.

    Why do I call it superheated?
    http://en.wikipedia.org/wiki/Geyser

    Read the section about ERUPTIONS. It's the same effect. Transparent fuel rails anyone! I bet Nissan has a few in the engineering R&D archives. Why the injector cooling fan in the ZX? Still no answers. Do I hear crickets?

    For carbs, you can build heat sheilds, try other fuel brands, pop the hood, insulate the lines...all the same thing EFI cars can do really.


    newsflash...do I see posts from VERY knowledgable people about EFI cars vapor locking?

    http://forums.hybridz.org/index.php/...58#entry949958
    So, speaking of crickets, has your theory changed so you no longer espouse the idea that vapor can't burn?
    And it sounds like you buddies on Hybrid Z are having a hardware issue. Maybe a clogged pre filter causing a low pressure area before the fuel pump leading to cavitation or vapor lock like conditions.
    Superheating has a specific definition that can be found here..http://en.wikipedia.org/wiki/Superheating.
    It may or may not exist inside the injector and is irrelevant. The Geyser effect is more likely and is commonly experienced by folks who think completely releasing a radiator cap on a 110 degree day after driving around for an hour is a good idea.

    So are you recanting on your "vapor will not burn" position?

    Steve

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    Of course vapor burns, but fuel pumps are not good at pumping vapor, and injectors flowing vapor bubbles into the intake cannot deliver enough molecules of fuel to ignite the charge properly. Did I say vapor doesn't burn? I said it would require different conditions. What I referring to was concentration.
    Last edited by cygnusx1; 07-29-2011 at 06:40 AM.
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    Quote Originally Posted by cygnusx1 View Post
    The pressure in the fuel feed lines is 34psi. What you have is a gradient of pressure tapering from 34psi down to vacuum. Somewhere in that gradient path, from fuel pump to pintle, there is a point, eg. 10psi, where the superheated fuel will vaporize. That point could be in the injector body, the hoses, or the rail. You end up with vapor pockets. Now for a few seconds, or minutes, you have vapor passing intermittently through the injectors.
    Nice description of the gradient path, and I'm with you.

    Assuming the temperature is high enough, somewhere between fuel pump and the intake valve end of the pintle the gasoline will cross the phase change line from liquid to gaseous. Still not sure exactly where, but it seems from yours and others experiences that it's in a place that affects performance for the first few minutes of operation. I'm buying it.

    My only point of contention is that I'm still not seeing the "superheated" part and we are really running the risk of wandering off into the weeds with this part of the discussion so I will try once and then let it go.

    I believe the use of the term on the geyser page is a misnomer as well. I know you had to pass thermo, right? Just because you have a hot liquid under pressure does not "superheated" make. That just means you have a hot liquid under pressure. With all imperfections in the rock surfaces and turbulence in the water, I can tell you that there's no superheating in a geyser. It's too unstable for that.

    You can change phase and flip back and forth across the liquid/gas phase line all day by varying temp or pressure as your theory suggests without ever becoming "superheated".

    In order for a liquid to be superheated, it has to incorrectly exist in liquid form when conditions place it in the gaseous area of the phase diagram. In other words, your substance is at a temperature and pressure that SHOULD result in a gas, but you are incorrectly a liquid instead.

    Ask yourself the question "What is keeping it in liquid phase?"

    If the answer is "Pressure.", then you're not superheated.

    If the answer is "Uhhhhh... I don't know. It really SHOULD be a gas but it's not!!", then you're superheated.

    Does that make sense?
    Last edited by Captain Obvious; 07-29-2011 at 07:26 AM. Reason: typo

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    Dave, your flash vaporization theory makes sense to me too. It's noteworthy that Nissan played around a bit with the injector insulator design. Of course the purpose of the insulators is not electrical, but rather thermal. Why are insulators necessary? Flash vaporization in a heat-soaked engine. Makes sense.
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    Contributing further to the flash vaporization theory, any of you who cook know that you have to stir the spaghetti sauce carefully if it's been simmering for a while. As soon as your spoon rubs the bottom of the pot, superheated liquids can explode into steam, splattering sauce all over your clean clothes. I wonder whether the movement of the injector parts similarly results in the vaporization of superheated fuel.
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    Quote Originally Posted by cygnusx1 View Post
    Of course vapor burns, but fuel pumps are not good at pumping vapor, and injectors flowing vapor bubbles into the intake cannot deliver enough molecules of fuel to ignite the charge properly. Did I say vapor doesn't burn? I said it would require different conditions. What I referring to was concentration.
    Yes, you did say vapor doesn't burn and there was no mention of concentration or any other qualifier.



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    Too bad we can't just open the horse's mouth...

    http://www.lhup.edu/~dsimanek/horse.htm

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    We could probably open the horses's mouth if we had a clear fuel rail and clear injector tubes. However what we do have: Difficulty hot starting some EFI Datsuns, rough idle when first started from hot, then we have datalogs of injectors feeding leaner mixtures as they heat up with a constant pulsewidth, and we have evidence that Nissan's engineers were still working on the issue from 1975-1983 by the design evolutions they made. Also, but not evidence, superheating, is relevant to this theory. In fact it's a critical point.

    Counter evidence is that some EFI Datsuns have never exhibited this, and the manual says it can't happen.

    We also know that fuel can boil pretty readily at engine bay temperatures, and atmospheric pressure....

    And finally we have this:
    Vapor lock questions for the hotter climate guys-side_feed_rx7.jpg
    The later generations of injectors are called SIDE-FEED because they are almost fully immersed in the fuel rail flow path. Why do you think they are bathed in the fuel path?
    Last edited by cygnusx1; 07-29-2011 at 02:29 PM.
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    Quote Originally Posted by Captain Obvious View Post
    Nice description of the gradient path, and I'm with you.

    Assuming the temperature is high enough, somewhere between fuel pump and the intake valve end of the pintle the gasoline will cross the phase change line from liquid to gaseous. Still not sure exactly where, but it seems from yours and others experiences that it's in a place that affects performance for the first few minutes of operation. I'm buying it.

    My only point of contention is that I'm still not seeing the "superheated" part and we are really running the risk of wandering off into the weeds with this part of the discussion so I will try once and then let it go.

    I believe the use of the term on the geyser page is a misnomer as well. I know you had to pass thermo, right? Just because you have a hot liquid under pressure does not "superheated" make. That just means you have a hot liquid under pressure. With all imperfections in the rock surfaces and turbulence in the water, I can tell you that there's no superheating in a geyser. It's too unstable for that.

    You can change phase and flip back and forth across the liquid/gas phase line all day by varying temp or pressure as your theory suggests without ever becoming "superheated".

    In order for a liquid to be superheated, it has to incorrectly exist in liquid form when conditions place it in the gaseous area of the phase diagram. In other words, your substance is at a temperature and pressure that SHOULD result in a gas, but you are incorrectly a liquid instead.

    Ask yourself the question "What is keeping it in liquid phase?"

    If the answer is "Pressure.", then you're not superheated.

    If the answer is "Uhhhhh... I don't know. It really SHOULD be a gas but it's not!!", then you're superheated.

    Does that make sense?
    Perfect sense.

    Steve
    Last edited by doradox; 07-29-2011 at 03:16 PM.

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    I well know what superheated means. Water at standard pressure that is at 213 deg F and not boiling, is superheated. The reason I bring superheated into my theory is that once the pressure is dropped, or the vibration of the pintle is started, THAT alone could bring the fuel to change phase, from a superheated state, or even just skipping the superheated state. Yes, it could all happen without ever being superheated. There is also hysteresis between the phases. So maybe there is some instantaneous point in time when the fuel is superheated, maybe it just vaporizes without ever becoming superheated. I don't know for sure. Fastwoman is right in the cooking pasta observation. Microwaving pure water, which boils the instant you drop something into it, is another example of superheated water gone wild. Superheated states, are highly unstable, which would make a liquid in this state much more likely to vaporize by a seemingly insignificant catalyst.
    Last edited by cygnusx1; 07-29-2011 at 04:51 PM.
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    Please forgive me for not knowing the intricate details of the Z's FI system, but...

    You made mention earlier of the batch type injection concept where that all the injectors open at the same time for the same duration. Is that what the 280Z uses?

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    Quote Originally Posted by cygnusx1 View Post
    So maybe there is some instantaneous point in time when the fuel is superheated, maybe it just vaporizes without ever becoming superheated. I don't know for sure.
    Quote Originally Posted by cygnusx1 View Post
    Also, but not evidence, superheating, is relevant to this theory. In fact it's a critical point.
    So is superheating critical to your theory or is it something that maybe sort of might be happening? Can cogently explain why superheating is a critical point?

    Steve

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    I am pretty sure that the old fuel injection systems in the S30's use full batch fire. All the injectors fire at once so you do have quite a bit of pressure bounce. The fuel damper is way at the back of the car too. Superheating may or may not be critical to the theory. But I now think it is. I just figured that a single injection happens pretty quickly (2-5ms), so the if the fuel is phase changing, it's happening pretty quickly. A liquid in a superheated state would be the first, and fastest to flash. So if you have a column of liquid with a pressure gradient, "above boiling pressure" at one end, and "below boiling pressure" at the other end. Naturally, somewhere in that column there is a segment of critical pressure. There is also a place in that segment where a smaller segment of superheated liquid lives. That small segment may be the "seed" for the instant flash, so to speak. This is really getting microscopic, but it's all perfectly feasible and I think it happens. It happens when the conditions, and fuel quality, fit the mold.
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    Quote Originally Posted by cygnusx1 View Post
    I am pretty sure that the old fuel injection systems in the S30's use full batch fire. All the injectors fire at once so you do have quite a bit of pressure bounce. The fuel damper is way at the back of the car too. Superheating may or may not be critical to the theory. But I now think it is. I just figured that a single injection happens pretty quickly (2-5ms), so the if the fuel is phase changing, it's happening pretty quickly. A liquid in a superheated state would be the first, and fastest to flash. So if you have a column of liquid with a pressure gradient, "above boiling pressure" at one end, and "below boiling pressure" at the other end. Naturally, somewhere in that column there is a segment of critical pressure. There is also a place in that segment where a smaller segment of superheated liquid lives. That small segment may be the "seed" for the instant flash, so to speak. This is really getting microscopic, but it's all perfectly feasible and I think it happens. It happens when the conditions, and fuel quality, fit the mold.
    Isn't it also possible that ALL the contents of the injector are already vapor before the injector opens? I think it would be more likely than your scenario where the exact conditions for the existence for some, however small, amount superheated liquid have to be present to cause the fuel to experience the phase change at exactly the moment required for it to cause a problem. So to my thinking, superheating isn't critical to explain vapor induced drivability problems in EFI cars.

    I think your tortured hypothesis may be possible but not one that Occam's razor wouldn't slice the heck out of when speaking , in general, about drivability problems suspected to be caused by fuel, heat, and pressure not playing well together in an EFI system.

    Steve

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    Yup that is possible. But according to the manual, it's not. Then again, the earth was flat once.
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    Thanks for digging up that tidbit, Dave! I think that MIGHT be another mystery solved. Now I won't fret so much when my hot engine re-starts roughly. Maybe the solution lies in a different design of injector.

    BTW, I forget who mentioned Datsun's tidbit about goosing the throttle for a hot start, but I don't think that will help much. I've tried goosing the throttle AFTER starting, and the engine still runs roughly. It doesn't even out until I pull out of the driveway and head down the road.
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    There is not much you can do to clear the vapor, other than drive it a bit after it starts. Sometimes it barely idles, so you can rev it, but the best thing is to place a moderate load on the engine which will open the injectors fairly "wide". Leaving the hood open is usually enough to prevent it in the first place. I wonder if any additives can raise the vapor pressure of the fuel, for experimentation.
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    Quote Originally Posted by cygnusx1 View Post
    Yup that is possible. But according to the manual, it's not. Then again, the earth was flat once.
    That, I think, stems from the definition of "vapor lock" which seems to have now evolved to mean any vapor related drivability problem. In the 70s maybe not so much.

    Steve

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    Wow, I broke a few ribs falling down a flight of steps Tuesday night and have been laid up for a few days. I assure you it is painful, but not as painful as this thread has become.

    SUPERHEATING
    The state of pretty much any matter depends on two things, temperature and pressure. Molten rock, for instance, in a liquid state can be subjected to enough pressure as to freeze back into a solid state, regardless of temperature. Likewise, under the proper circumstances, solid rock can be subjected to a sufficient bombardment of thermal energy as to cause it to go directly from a solid state to a vapor state, as demonstrated in volcanic eruptions. Superheating is a term which describes the amount of thermal energy that a given form of matter needs to absorb in order to change from a solid state directly to a vapor state, thereby skipping its liquid state altogether. Super heating has no place in a vapor locking discussion.

    EFI
    As for the FI discussion, when the injector opens, the orifice opens into a VACUUM, thereby radically altering the boiling point of the pressurized fuel, which would be aggravated by, fuel that is many degrees above the boiling point (at atmospheric pressure), along with the hot environment of the combustion chamber. This causes a lean condition (which at some point will become too lean to burn), detonation and other problems associated with the IC engine. The delta T of the specific fuel blend, the amount of mass the liquid fuel comes into contact with (once the pressure is removed from the fuel), the thermal coefficient and temperature of that mass being encountered by the fuel (the ability of the various metals to transfer heat) all play a roll in these conditions (there are many other factors which also have effects on combustion). The fact of the matter is, that as long as your fuel pump has access to liquid fuel and is able pressurize a closed system with that liquid fuel, any vapor will be sufficiently compressed as to return to its liquid state in short order. SO NO, AN EFI CAR CAN NOT SUFFER FROM VAPOR LOCK.

    CARBURATION
    Carbureted engines are completely different in so much as the fuel must exist in within the bowl, in a liquid state, at atmospheric pressure, in sufficient quantities, as to feed the jets with enough liquid fuel, that can be atomized again in sufficient quantities as to sustain combustion. The inability of the delivery system to supply an adequate amount of fuel to the carburetor bowl, is defined as VAPOR LOCK.

    THE QUESTION IS (WAS)
    What crafty little tricks have you desert dwellers come up with to minimize the vapor locking issues inherent to early Z’s?

    Seriously, I wasn’t trying to revisit Physics 101, I was simply looking for elegant solutions to the problem, so the car runs well in hot weather, the engine compartment stays as uncluttered as possible, and I don’t drain my bank account. I did enjoy the thread though.

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    Quote Originally Posted by 5thhorsemann View Post
    Wow, I broke a few ribs falling down a flight of steps Tuesday night and have been laid up for a few days. I assure you it is painful, but not as painful as this thread has become.

    SUPERHEATING
    The state of pretty much any matter depends on two things, temperature and pressure. Molten rock, for instance, in a liquid state can be subjected to enough pressure as to freeze back into a solid state, regardless of temperature. Likewise, under the proper circumstances, solid rock can be subjected to a sufficient bombardment of thermal energy as to cause it to go directly from a solid state to a vapor state, as demonstrated in volcanic eruptions. Superheating is a term which describes the amount of thermal energy that a given form of matter needs to absorb in order to change from a solid state directly to a vapor state, thereby skipping its liquid state altogether. Super heating has no place in a vapor locking discussion.

    EFI
    As for the FI discussion, when the injector opens, the orifice opens into a VACUUM, thereby radically altering the boiling point of the pressurized fuel, which would be aggravated by, fuel that is many degrees above the boiling point (at atmospheric pressure), along with the hot environment of the combustion chamber. This causes a lean condition (which at some point will become too lean to burn), detonation and other problems associated with the IC engine. The delta T of the specific fuel blend, the amount of mass the liquid fuel comes into contact with (once the pressure is removed from the fuel), the thermal coefficient and temperature of that mass being encountered by the fuel (the ability of the various metals to transfer heat) all play a roll in these conditions (there are many other factors which also have effects on combustion). The fact of the matter is, that as long as your fuel pump has access to liquid fuel and is able pressurize a closed system with that liquid fuel, any vapor will be sufficiently compressed as to return to its liquid state in short order. SO NO, AN EFI CAR CAN NOT SUFFER FROM VAPOR LOCK.

    CARBURATION
    Carbureted engines are completely different in so much as the fuel must exist in within the bowl, in a liquid state, at atmospheric pressure, in sufficient quantities, as to feed the jets with enough liquid fuel, that can be atomized again in sufficient quantities as to sustain combustion. The inability of the delivery system to supply an adequate amount of fuel to the carburetor bowl, is defined as VAPOR LOCK.

    THE QUESTION IS (WAS)
    What crafty little tricks have you desert dwellers come up with to minimize the vapor locking issues inherent to early Z’s?

    Seriously, I wasn’t trying to revisit Physics 101, I was simply looking for elegant solutions to the problem, so the car runs well in hot weather, the engine compartment stays as uncluttered as possible, and I don’t drain my bank account. I did enjoy the thread though.
    Superheating. Not commonly defined as you have but I agree that it's not relevent.
    http://www.answers.com/topic/superheating
    http://www.wordiq.com/definition/Superheating
    http://en.wiktionary.org/wiki/superheating

    Any vapor "can" be compressed enough so it won't turn to vapor at any temperature. But the fuel pump in an EFI system is regulated to a max pressure therefore if the fuel temp is high enough it most certainly can vaporize. Whether or not this is called vapor lock is another thing altogether. I'm with you on the definition though as vapor lock has been around since the dawn of carbureted IC engines.


    Pop your hood when you park for short periods on hot days. Cheap.

    Move the fuel filter to the pressure side of the pump. A restricted filter lowers the pressure on the inlet side of the pump.
    Marginal if any benefit.

    Get an electric pump and mount it low in the engine compartment or move it completely out. The high mounted manual pump means lower fuel pressure on the inlet side of the pump and exposure to some of the hottest air in the engine compartment.

    Electric radiator fans with a thermostatic or timed cut off and wired to run with the ignition off will create air flow and help reduce heat soak. Make sure your battery is up to the task though.


    Steve
    Last edited by doradox; 07-30-2011 at 02:45 PM.
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    Ouch sorry to hear about the ribs. That's one of the most painful things, and I can't image our discussion has been that painful. Sorry you had to read it all.

    I am not sure where you get your definition of superheating. It seems like you are talking about sublimation, perhaps? Whatever, really. I think we have figured out that an EFI system can get vapor in it, but it's not as critical as with a carbureted system because it should never effect the pumping of the fuel.

    Depending on what problem the vapor causes, it may be called vapor lock, or not. Maybe we can just say, "my Z has the vapors", when it's not causing pumping issues.

    Question though. Isn't vapor lock really just pump cavitation anyhow?

    Tricks? A long time ago, I added 1/8" thick teflon washers between the fuel rail mount tabs and the intake manifold. I also had wrapped the fuel lines with a glass backed foil at one point. By far the best result has come from leaving the hood popped at least 10".
    Last edited by cygnusx1; 07-30-2011 at 05:34 PM.
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    Quote Originally Posted by 5thhorsemann View Post
    Seriously, I wasn’t trying to revisit Physics 101, I was simply looking for elegant solutions to the problem. I did enjoy the thread though.
    I'm guilty as charged, and I apologize. I would like to be the first to admit that I've offered nothing to help with your original question. I found the topic interesting and got sucked in with the intent of defending the laws of physics. And just when I thought I would be able to resist, : something like this happens...

    Quote Originally Posted by doradox View Post
    Any vapor "can" be compressed enough so it won't turn to vapor at any temperature.
    Uhhh... No.

    There exists a temperature (shown on the phase diagram I linked to earlier as Tcr) called the "critical temperature". The critical temperature of a substance is the temperature at and above which vapor of that substance cannot be liquefied, no matter how much pressure is applied. In other words, above Tcr, there can be vapor only. No liquid, and certainly no solid. (Haha! Ignoring superheating, of course.)

    I'm really trying to give up the physics. Really!! As a matter of fact, thermo was my worst class ever. I absolutely hated it.

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    Quote Originally Posted by Captain Obvious View Post
    I'm guilty as charged, and I apologize. I would like to be the first to admit that I've offered nothing to help with your original question. I found the topic interesting and got sucked in with the intent of defending the laws of physics. And just when I thought I would be able to resist, : something like this happens...



    Uhhh... No.

    There exists a temperature (shown on the phase diagram I linked to earlier as Tcr) called the "critical temperature". The critical temperature of a substance is the temperature at and above which vapor of that substance cannot be liquefied, no matter how much pressure is applied. In other words, above Tcr, there can be vapor only. No liquid, and certainly no solid. (Haha! Ignoring superheating, of course.)

    I'm really trying to give up the physics. Really!! As a matter of fact, thermo was my worst class ever. I absolutely hated it.
    Yeah, your right, it was a little hyperbole more than anything.

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    Quote Originally Posted by cygnusx1 View Post
    I am pretty sure that the old fuel injection systems in the S30's use full batch fire. All the injectors fire at once so you do have quite a bit of pressure bounce. The fuel damper is way at the back of the car too.
    So is the damper intended to reduce changes in pressure in the positive, or negative direction, or both? In other words, suppose your fuel rail is supposed to be at 30 psi... Is the damper supposed to provide some temporary volume to swamp out pulses above 30 psi, or supply a transient supply of fuel in the event that the fuel pressure drops below 30 psi? Or both?

    I've never thought about it that intently before. You got any idea?

    I mean, who knows what's happening at speed. You got the injectors are opening and closing. They open and fuel goes out, so physics dictates that the pressure must drop. And then they snap shut, probably momentum hammering the fuel rail and sending a very high spike back through the line. And then you have the fact that the pump output is probably not be a perfectly steady pressure either.

    So what's your take on the damper?

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    Quote Originally Posted by doradox View Post
    Yeah, your right, it was a little hyperbole more than anything.
    The really unfortunate thing for me is that the main reason I hated thermo so much was that I (at the time) saw absolutely no practical application for it in my future. I barely squeaked through!! Little did I know...

    If I had known then how much of it was easily applicable to automotive applications, I would have paid attention. There is so much more that I could have gotten out of it if I simply would have given a crap. The stupid things you do that don't seem stupid until later.

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    Quote Originally Posted by Captain Obvious View Post
    The really unfortunate thing for me is that the main reason I hated thermo so much was that I (at the time) saw absolutely no practical application for it in my future. I barely squeaked through!! Little did I know...

    If I had known then how much of it was easily applicable to automotive applications, I would have paid attention. There is so much more that I could have gotten out of it if I simply would have given a crap. The stupid things you do that don't seem stupid until later.
    I entered engineering after 20 years of wrenching as an ASE Master tech and really loved learning the math and physics behind all the things I had learned from experience. It made even thermodynamics kinda fun.

    Steve

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    Common we can get this thread to 100 posts!

    I think that since the damper was so close to the fuel pump, Nissan enginerds have it in there to dampen the pulsation from the pump. They didn't make obvious provisions for the injectors pulsing the rail pressure.
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    Quote Originally Posted by cygnusx1 View Post
    Common we can get this thread to 100 posts!

    I think that since the damper was so close to the fuel pump, Nissan enginerds have it in there to dampen the pulsation from the pump. They didn't make obvious provisions for the injectors pulsing the rail pressure.
    Would you say the damper is for the benefit of NVH or?

    Steve

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    Quote Originally Posted by cygnusx1 View Post
    I think that since the damper was so close to the fuel pump, Nissan enginerds have it in there to dampen the pulsation from the pump. They didn't make obvious provisions for the injectors pulsing the rail pressure.
    So there's nothing up in the engine compartment to mitigate high frequency pulses? You've got the FPR up there for low freq stuff, but nothing for high frequency effects like the injectors opening and closing?

    I'm wondering if there was a device close to the injectors capable of dealing with high frequency effects and regulating the fuel pressure better than the FPR, it might help with the very hot restart issues we were discussing. The thinking being that it might do a better job of regulating the pressure locally and preventing any vapor from forming in the system, even if that vapor is a recurring transient.

    Quote Originally Posted by doradox View Post
    I entered engineering after 20 years of wrenching as an ASE Master tech and really loved learning the math and physics behind all the things I had learned from experience. It made even thermodynamics kinda fun.
    Yeah, I went the other way. Engineering first. I would have gotten more out of it if I'd done it the way you did. Heck... Maybe even fluid dynamics and strengths of materials would have been ummm.... dare I say tolerable?

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    Do you really think a high frequency damper would do anything to improve fuel delivery at RPMS over 1000 to 1500? On a 6 cyl your lines see 3000 PPM or 50 pps at 1000 RPM. The gasoline is light enough alone, adding the ethanol makes it even lighter, I wonder where the pressure pulse would flatline, RPM wise. If you look at how a hydraulic system behaves (using hyd. fluid, or brake fluid, which are heavy and dense compared to gasoline) at low (pump) rpms the systems are slugish and you can feel the vibrations through the controlls, like peddal feedback on brakes. But if you rev the whole thing up it gets smooth as silk. I would think the gasoline would act as its own shock absorber at a very low rpm. Anyone running a mechanical fuel pressure gauge that can speak to that?

    Back to the VL. I'm using pheonalic washers on my fuel line at the head, same stuff the carb heat isolators are made of. The hard lines are wrapped in fiberglass and have a 3 mil. reflective aluminum shield tape (one layer thick) over the FG. The fuel filter is before the pump, and mounted at about the same height, thats how I came to the VL conclusion so quickly. I could see that the filter was empty, and when it did begin to fill the fuel was boiling within the filter itself. I think the pusher pump is going to be my savior on this one, and I also think I am just going to stick the Faucet pump back at the tank because the existing mounts and wiring will fit rite up, after all, it's cheep enough and they are very dependable from what I've heard and read.

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    Quote Originally Posted by Captain Obvious View Post

    Uhhh... No.

    There exists a temperature (shown on the phase diagram I linked to earlier as Tcr) called the "critical temperature". The critical temperature of a substance is the temperature at and above which vapor of that substance cannot be liquefied, no matter how much pressure is applied. In other words, above Tcr, there can be vapor only. No liquid, and certainly no solid. (Haha! Ignoring superheating, of course.)
    I was thinking about this and something didn't seem quite right. If a liquid held at a constant volume is heated past the critical point how would the "gas" that now exists be any different than the liquid. Apparently it isn't.

    http://en.wikipedia.org/wiki/Phase_%28matter%29

    "At the critical point, the liquid and gas become indistinguishable. Above the critical point, there are no longer separate liquid and gas phases: there is only a generic fluid phase referred to as a supercritical fluid. "

    So a gas can be compressed to at least a state which is not a gas anymore.

    Steve

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    Quote Originally Posted by doradox View Post
    I was thinking about this and something didn't seem quite right. If a liquid held at a constant volume is heated past the critical point how would the "gas" that now exists be any different than the liquid.

    So a gas can be compressed to at least a state which is not a gas anymore.
    Haha! Did you look at the list of references for that page and the ones similar? It looks like someone is bucking for a good thesis grade. A lot of the references cited are less than five years old and lots of them are clearly research!

    This is my favorite... Number 25:
    Ye, Xiang-Rong; Lin, YH and Wai, CM (2003). "Supercritical fluid fabrication of metal nanowires and nanorods templated by multiwalled carbon nanotubes". Advanced Materials 15 (4): 316–319. doi:10.1002/adma.200390077.

    Now there's a citation I can trust!

    As a matter of fact, I was just messing with some metal nanowires and nanorods templated by multiwalled carbon nanotubes yesterday in the shop.

    Seriously though, good catch. Research continues and concepts are refined. Haha! Back when I was in school, we got by just fine with only three phases. Seems they weren't teaching this at your school either, huh?

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    Quote Originally Posted by 5thhorsemann View Post
    Do you really think a high frequency damper would do anything to improve fuel delivery at RPMS over 1000 to 1500? On a 6 cyl your lines see 3000 PPM or 50 pps at 1000 RPM.
    It really doesn't matter, but I don't get your math...

    I do this:

    Assuming batch fired injectors on a four stroke engine...

    At 1000 rev/min there are 500 injections/min
    500 injections/min = 8.3 injections/sec

    Do I think a high frequency damper might be able to do something to quiet 8.3 pulses per second?

    Yes.

    Back to the VL.
    On your VL issues, it sounds to me (the non-expert on such matters) that you're doing everything right except for the removal of the pusher pump.

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    Quote Originally Posted by cygnusx1 View Post
    Common we can get this thread to 100 posts!
    100!
    My last three sports cars while I still owned all three:

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