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Vapor lock questions for the hotter climate guys

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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.

Edited by cygnusx1

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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.

Edited by cygnusx1

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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... ;)

Edited by FastWoman

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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.

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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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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I was doing a little light reading and found this little tidbit in the 76 FSM.

[ATTACH=CONFIG]46950[/ATTACH]

Damn-ya beat me to that one.

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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.

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.

Edited by cygnusx1

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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.

__________________________________________________________________________________________________________

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.

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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.

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.:tapemouth

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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-related/Diagnosing-Returnless-Fuel-Injection-Systems.htm

Edited by cygnusx1

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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... :ermm:

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. :D

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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! LOL 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? :eek:

http://forums.hybridz.org/index.php/topic/101376-vapor-lock/page__pid__949958#entry949958

Edited by cygnusx1

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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! LOL 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? :eek:

http://forums.hybridz.org/index.php/topic/101376-vapor-lock/page__pid__949958#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.

Edited by cygnusx1

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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?

Edited by Captain Obvious
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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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.

post-14809-14150815751373_thumb.jpg

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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:

post-4964-14150815751786_thumb.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?

Edited by cygnusx1

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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

Edited by doradox

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