'76 280Z Question on dist/manifold vacuum, dist timing, fuel pressure, brake booster

[FastWoman]

You go, girl!

I'm glad your Z is running better now! It's a great feeling, isn't it!

[Bonzi Lon]

You might want to replace the chalk mark, which could wash off, with 'Liquid Paper' or a silver 'Sharpie'. A tip from the forums. Fingernail polish too.

Bonzi Lon

[Jennys280Z]

*grumbles* Well I think I spoke too soon! It seems that just idling the car wasn't enough of a test. Though I can verify that all cylinders are getting spark and that's not the problem, the car's RPMs dropped abnormally as soon as I put it in reverse and released the clutch. When it's running normally I don't even have to blip the gas. Just put it in reverse, gently release the clutch and the RPMs drop a little I guess but it pulls right out of the garage with no gas necessary. As it's running now the RPMs dipped down to like 400-500 and it might have even stalled if I didn't tap the gas a few times to get it rolling. First gear was the same as I lined it up in the driveway the RPMs dipped, the chug-chug became more noticeable. I guess when the engine is loaded with the car and it's not in neutral the problem is more severe than in idle (eliminating vacuum leak as the problem I would guess).

So if ignition and vacuum are ruled out, what else? It doesn't backfire but the idle speed in neutral spikes between anywhere between 770 and 860RPM the way I left it. Timing seemed good before (right on 10BTDC) but I'm going to check it again today because I might have misread what the little points on the plate mean. I took a photo, labeled it, and will post it here for posterity. There aren't enough photos of this kind of stuff on the internet as it is. I'm also including a photo of where my distributor body's timing is set just in case it looks unusual to anyone. I'm guessing that turning it counterclockwise advances the timing?

So the problem seems constant, most noticeable in gear, no black smoke (or any smoke), slight smell of gas (normal), no power and a rough running/idling engine. The blub-blub-blub in neutral sounded great but when I drove it....it blub blubbed with no power down the street too!

All the vacuum hoses mentioned above have been replaced and so that's all in better shape than ever. The car was running fantastic and literally the next one or two times I started it up, it's right back to this again! Does timing go out all of a sudden like this? Does an AFM break, then work, then break again?

The motor starts very easily. It fires right up in a fraction of a second every time. It just doesn't want to run right! I'm going to buy the fuel pressure gauge and fitting linked to above, get a new section of hose and four clamps, cut it to fit and then it'll be optional whether I decide to use it permanently or not.

Someone on the board once mentioned that there's a filter in the nose of the fuel pump that can get clogged. Can I inspect/remove that filter in the fuel pump without removing the fuel pump? The fuel pump on there now, while it sat in storage for a long time, hasn't seen very many miles.

The ignition coil...I have read that they either work or they don't and that one shouldn't expect that it's delivering "weak" spark.

My car still reads too cool on the temp gauge. It's slow to get off of 120 and slowly rises to about ~140 and sits there. Doubt this is related to how the engine runs.

Any advice on "next place to look" would be awesome! Thank you. Check the photos out too! xx

Oh yeah, the craziest thing of all when you look at this photo? Just randomly shutting the motor off, the timing notch on the crank pulley stopped exactly on the zero timing mark. I could try to duplicate that again a hundred more times and would never be able to do it twice. It's just one of those crazy things I guess.

Oh and disregard that chalk mark on the 15deg line. I just drew that on there to make sure that what I was looking at was happening north of that line...back when I thought that reading the timing would still be really hard even with the chalk marks on it. I'm going to remove that line and draw one at around 13deg and another one at 7deg and hope I'm somewhere between the two lines. I questioned disconnecting the temp sensor wire and grounding it like my 70-79 shop manual recommended. But my FSM from Tokyo said nothing of the sort. It just says timing is retarded when the engine is warmed up. 7degBTDC, setting advanced timing not required unless setting phase diff. How do mechanics dial in the timing accurately when the idle speed varies and the motor doesn't seem to warm up?

Edited November 27, 2010 by Jennys280Z

[cozye]

What's the fuel pressure ? What vacuum are you pulling ?

You need to replace the thermostat it sounds like for sure, sounds like it's stuck open. The EFI is directly affected by water temp and although it may not be the source of your issue, you will have a hard time getting this car tuned right with it running cold all the time.

[FastWoman]

Wow, a lot of issues addressed here! Answers to questions are generally much longer than the questions themselves. Anyway, I'll take a cursory stab:

First of all, timing on an electronic ignition engine (like yours) is remarkably stable over time (as long as you tightened the set-bolt at the base of the distributor (pictured in your righthand photo). Once you've got it set right, I doubt you'll ever have to re-time it again.

You can raise your idle speed by adjusting the big screw on top of the throttle body. However, if your idle speed isn't as high as it was, something else is probably wrong.

You could have a clogged fuel supply. That would probably be evident in the fuel pressure under the conditions at which the engine isn't running correctly -- in your case at idle.

It could be an ignition problem, but usually ignition problems are more evident at high RPMs, when output demand is higher. Put your timing light on each of your spark plug wires to see whether there are any "skips" in the flash pattern.

Your idle shouldn't sound like "blub blub." That's what a V-8 engine sounds like -- the classic (V8 burble). Instead, the exhaust on an inline 6 engine should have a smooth, low-pitched "hum," for lack of a better word -- more like a very low note on a tuba than something from the Dukes of Hazard. On a poorly running engine, there may be occasional misses, where a puff is missing, or where the engine shoots out a puff that is much harder than the others. If there's a regular and rhythmic chug, chug, chug, then that indicates a specific cylinder that isn't firing. You can find it by pulling spark plug wires one by one. If/when you pull one one that makes no difference to the running of the car, that's your dead cylinder. It could be either an ignition problem (e.g. fouled spark plug, bad spark plug wire, short to ground), an injector that's not firing (no electrical contact, clogged, malfunctioning), something wrong in the valves, or even a blown head gasket (in which case you'd probably notice lots of other awful stuff too).

If the missing is randomly timed, and if misses are somewhat infrequent, then you could have sticky valves, particularly if the car has spent a lot of time sitting or has been poorly maintained. You can free up sticky valves with a Sea Foam treatment or an engine flush (Gunk). People often have very strong feels that you shouldn't flush your engine, but it's always worked well for me. Sticky valves also get better with regular use.

Probably a more likely cause of random missing is an incorrect fuel/air mixture. Contrary to my expectations, I could still smell a hint of gas in my exhaust when I was running much too lean. That's because of the misses, when the lean, unburnt fuel/air mixture is ejected into the exhaust. When this happens, I think the mixture detonates in the exhaust, causing a hard puff, but it burns very inefficiently, resulting in the hint of gas smell in the exhaust.

If your engine is running too rich, the smell of gas in the exhaust will be rather strong, and you may see some black smoke, especially on full-throttle acceleration.

If your engine is running too lean, the exhaust will blow too hard, with occasional hard puffs.

A better way to diagnose fuel air mix problems by reading your spark plugs. Do a google search for "read spark plugs." You'll want to install a fresh set and run them for maybe 100 mi before reading them.

There are MANY reasons why you might have the wrong fuel/air mixture. If you read through my "what next" and "purs like a kitten" threads, you'll see all I did to diagnose and correct my own fuel mixture problems.

Aside from suggesting general areas to look, it's hard to make more specific recommendations. You're going to have to do a lot of sleuthing on your own. My advice is to do the following:

1. Make absolutely certain your intake system has no more vacuum leaks. To do this, remove the air flow meter from your car -- 3 bolts on the base, two possibly crumbly boots (replaceable through MSA), and a fat electrical connector at the base that has a small spring clip that must be opened with a small screwdriver to be removed. Stuff a yogurt cup into the boot going to the throttle body. Now pull the brake vacuum line and HVAC vacuum line (the small one beside it) from your intake manifold. Connect a clean hose to the brake vacuum fitting. With your finger covering the HVAC vacuum fitting, blow through the hose to "inflate" the intake system. It should take maybe 10 or 15 seconds for the pressure to start declining. You'll be able to feel the rate of leakage. Now do the same thing without your finger over the HVAC fitting. You're introducing a known leak by doing this, and you should feel the pressure decline quite a bit faster (e.g. a few seconds). If the first test seems quite a bit tighter than the second, you probably have no vacuum leaks. Of course don't forget to test the other direction to see if you have leaks in your HVAC or brake system. Once you know your intake is tight, then...

2. Use both your factory service manual and the "fuel injection bible" (downloadable online) to troubleshoot your system.

3. In addition to a fuel pressure gauge, buy a vacuum gauge. It will tell you quite a lot about how efficiently your engine is running.

... and yes, what Cozye said. Correct all known issues as soon as you discover them, or else you'll be running around in circles. Even though the bad thermostat shouldn't make your engine run badly, it will prevent you from diagnosing the engine at normal operating temperature.

It can be a lot of work, but you should end up with a nicely running engine.

Good luck!

Edited November 27, 2010 by FastWoman

[Jennys280Z]

Thanks for the help! I love you guys! I love everyone who drives a Datsun even if they think I'm annoying ...well...A few of the things y'all mentioned here might be beyond me but I'll do more homework online and offline when I have time. Right now I'm so bummed I don't even want to think about my car after I type this!

A short update:

I took the car for a ride. It ran badly as expected. Like a constant miss. Brrrrr-brrrrr-brrrrr-brrrrr-brrrrr and when I applied throttle it keeps doing it but more like brrr-brrr-brrr-brrr-brrr-brrr . I tried to take some video but I don't know how it turned out. My camera ran out of memory really fast because I left it full of pics so...but...I'll try to get it on the PC and upload it and link it here later. *sigh* Okay...

A few months ago I replaced all the spark plug wires with new NGK wires. NGK spark plugs are all in great shape with less than 1000 miles on them. Dist looks great.

Fuel pressure is still unknown because I just ordered the gauge and fitting last night. It is expected to ship Monday and I should have it before next weekend I hope. I'll post the results then. But do I have to disconnect the wire at the fuel pump and the starter and the negative battery cable and all this stuff just to take a fuel hose off and install a fuel filter or a gauge??? Gawd what for???

I spent a long time with the timing light today and I began to feel like we were one and I became entranced by the flashing lights. My timing is indeed right at 10degBTDC and seemed to stay pegged right there regardless of how long the engine idled/warmed.

The RPMs were up in the 900s right after I started the motor up and then it gradually came down into the 800s. I spent a good minute or two on every spark plug wire with the timing light. There's a good strobe with every wire. No missing flashes at all that I could tell.

Intake manifold vacuum fluctuates between 13-14 in.Hg at 1145 ft above sea level at 800 RPM. I played with the accelerator pedal while the gauge was hooked up at the brake booster connector at the intake manifold per Atlantic Z and also because I had that taped shut anyway since my brake booster is shot. When I hit the gas the vacuum shot down to 5 in Hg quickly and then read as follows: 15-16 in. Hg at 1200 RPM. 18"Hg at 1600 RPM.

I noticed while I was dialing in the idle speed screw, I would hear a hissing noise that seemed to come and go. I would turn down the idle a quarter turn and I would hear it, then turn the idle down s'more and it'd go away. Make another quarter turn and I'd hear it again...and so forth.

As the motor warmed up I was able to get a fairly stable idle between 790 and 820RPM, with an occasional run up to 830 or 840 which would only last a second or two.

I had no idea there was an HVAC line that could be leaking vacuum connecting to the intake manifold. I don't know where this connects at. I'll do more homework about this later.

There's a tinny-metallic rattling-vibrating noise that might be getting more severe that sounds like it's coming somewhere either under my dash or through the floor where the transmission is. I've heard this sound before now though it was a bit more pronounced today. Trannys and clutches are definitely beyond me so I don't want to discuss working on those , just mentioning the sound for diagnostic reasons. heh

Temperature gauge never went past 135 degrees today in about 55 degF outside temp. I cleaned the temp sensor and the thermotime electrical connectors earlier this year with some Deoxit. My oil pressure always notoriously read low until I cleaned that sensor near the oil filter and now my gauge reads higher than ever (it actually moves off the zero when I apply some light throttle ). Cleaning the temp sensor seems to have had the opposite effect on my temp gauge! j/k it's probably the thermostat. I see that black dragon has them (had?) for about $10 and the two little gaskets are a few bucks apiece. I might order a new parking brake boot, throttle boot (mine is falling apart), and I wish what I really need more than anything, a LOCKING GAS CAP, but alas they don't have any for a '76 model, and I can't find one for sale anywhere (I used to have one too! *cries*).

I have an aftermarket air conditioning on this car but it isn't charged up and I doubt it would work anyway. Earlier this year I took the A/C belt off the compressor pulley and then tightened the alternator belt which was very loose. It's tight now the way it should be though the belt is old and I can see it slipping a little when I'm using the timing light. I'm mentioning that I removed this belt because I never even thought that vacuum issues might relate to the heater/AC.

In one of my old threads my car was running so awesome too! rmember? But GRRRR that didn't last long! It's so frustrating when nothing happens to my car but it sits in the garage, and then the next time I start it, it's horrible again from out of nowhere! Really down and out right now so I'm going to grab a bite out and then maybe post that video later or tomorrow if it sounds/looks informative.

I have downloaded and printed the EFI Bible which is for a '75 280Z and I ran all the relevant tests from the ECU which I posted on the board. Everything seemed okay...the resistances for the AFM looked high, but then my car magically fixed itself for a while, which is why I mentioned I don't think the AFM can fix itself and then break again.

I guess the thing I could have done today but didn't is to start pulling spark plug wires and checking for differences. I'm kindof scared to do that. I guess I can do it tomorrow tho. *shrugs* I don't want to get gasoline in my oil again for nothing but what can a girl do??? When I pull a spark plug wire off (at the plug) and then start the car to check for a difference in how it runs, does the plug wire need to be grounded near some metal or can it just be sitting anywhere?

I guess the two questions in bold are the most critical ones that are giving me the most amount of headache not knowing the answers.

I need to eat dinner... going out and getting drunk too

Peace!

xx

Edited November 27, 2010 by Jennys280Z

[FastWoman]

Your bold-face questions:

Disconnecting electrical stuff before connecting up a fuel pressure gauge. My attorney would tell me to tell you you ABSOLUTELY HAVE TO DO ALL THAT STUFF. However, I don't personally do this. I just make certain I don't turn the ignition key and energize the fuel pump while the fuel system is open. My own safety measure is that the key goes in the ignition only when I'm testing something. When I'm done testing, and before I put my fingers into the engine or crawl under the car, the key goes in my pocket. However, this is only how *I* do things. For you, I'd officially recommend following the conservative advice of my attorney, if you know what I mean.

The spark plug wire test is done while the engine is running. Before you start, make sure all your spark plug wires are easy to pull off. Then start the engine and let it warm. Then grab a spark plug wire and pull it to see if the engine slows down. If the engine slows (and perhaps chugs), then the cylinder was firing correctly. Replace the plug wire, and move on to the rest. Precautions: Wear rubber gloves, and don't put your fingers too close to the tip of the spark plug wire. You don't want to complete the circuit. Also be VERY CAREFUL not to get too close to any moving parts, especially as you get towards the #1 cylinder.

Some people will point out this method is hard on the ignition system. They're right, but that doesn't stop some of us from using it. A better method is to buy a device you can put inline with the spark plug to short it to ground (??? I think). An even better approach is to pull loose an injector connector instead. No fuel = no fire. However your connectors are probably brittle/crumbly and might easily be damaged in the process. (They should probably be replaced. You can order some off of Ebay. You need to know how to solder electrical connections, use heat shrink, etc. -- not rocket science.)

Other matters:

Your vacuum is very low, but you know that. You should ideally have a reading of 19 at idle, but cozye and I are running about 18 on our engines. You should probably pull at least 17. You might be running lean. However, you're probably getting ahead of yourself. Your vacuum confirms that you have a problem. Now how to diagnose it?

I'd have to refer you back to my original approach. First, make certain you have no vacuum leaks. Your engine is properly timed, which is another important step. Also make certain all of your cylinders do something (by pulling wires). If you have a compression gauge, you might want to verify that you have normal compression in all of your cylinders. All of this will establish that your engine is mechanically sound and that your problem is a fuel delivery issue -- probably fuel/air mixture.

You've worked your way through the EFI bible and have verified that all your sensors are good, so you're quite far along. AFTER YOU'VE DONE ALL OF THE ABOVE, pull the black cover off of your air flow meter. (It's sealed with caulk, and you'll eventually need to re-caulk to reinstall it.) Make sure the mechanism moves freely, with no binding. Measure the voltage at the wiper connection (that center contact) with a mechanical volt meter (ignition on) to be certain it varies smoothly when you move the mechanism back and forth. Now with the engine idling, nudge the little counterweight mechanism a bit clockwise and then counterclockwise. Does the engine run much faster when you move it either direction by a very small distance (maybe 1/8") and much slower when you nudge it in the other direction? If so, then your fuel/air mix isn't optimal. If it runs better when you move the assembly counterclockwise, then your mix is too lean. If it runs better the other way, your mix is too rich. I think once you've gotten to this step, we'll be able to help you figure out where to look next.

Oh, finally, a note about the engine magically running well one moment and then the next: That's often something electrical -- a contact that sometimes fails and is sometimes good. Make certain all of your connections are clean and free of corrosion, including the one on the bottom of the air flow meter. Also clean the carbon trace and contacts underneath the air flow meter cover plate.

One more note: I've rarely seen a car older than 10 years that doesn't have multiple fuel issues. They can often work against each other, so that when you fix one problem it makes the engine run worse. Don't worry about it. Just go with it, and keep fixing problems as you find them. Eventually the engine will run great.

Peace back at'cha! (Too little of it nowadays.)

Edited November 27, 2010 by FastWoman

[cozye]

Pretty much what Sarah said. I'm thinking you will need to richen up your mixture, but you've got a lot of other troubleshooting and ruling out to do first for sure.

The only other thing I will ad is that if you don't want to go pulling our AFM apart, you can pull the throttle valve switch connector off, and take a small piece of wire to jumper the middle pin to the outside pin. If it runs a bunch better, then you are running to lean for sure. You can drive it with the switch jumpered for test. I can't remember which outside pin will be full enrichment. One pin will richen it just a little, the other will richen it quite a bit. This is a good test that only takes 5 minutes.

I would take care of that thermostat issue before you do anything else though. If your car won't get up to temp, your FI will richen the mixture up and it's going to get in the way or could even be your problem. Do you have a nice cooking thermometer, or maybe one for steaming milk for espresso ? Go for a drive and get the car hot. Come back and take the radiator cap off very carefully, relieve pressure before unlocking cap all the way. Put the thermometer in and see what it reads, this will rule out your water temp sending switch (since it's just for the gauge and not for the EFI). If it's only 130-140, then replace your thermostat.

Also, on the vacuum check, take vacuum reading with motor hot. When cold start is going on or AAR valve partially open, that will lower your vacuum. This also goes back to your motor running cold

[FastWoman]

What Cozye said about the throttle switch. (Good idea!) You can also pull off a vacuum hose to see whether the engine runs better (faster) or worse (slower). Better means your mix is too rich. Worse means your mix is too lean. He's also right that you need to resolve the thermostat issue before proceeding further.

I have to differ with the thermometer in the radiator water idea, though. The thermostat regulates how hot the water is inside the engine. The radiator water will be at entirely a different temp -- probably much cooler. If I were you, I'd go ahead and pull the thermostat out and test it in a pot of hot water on the stove with a thermometer. (Drain a bit of coolant before unbolting the top of the thermostat housing.) Once you've tested the thermostat, order in a new gasket from Autozone, and if you need it, which you probably will, order in a new thermostat along with it. Also while you're at it, it sounds like your oil pressure sender is bad. It's easy to fix. It unscrews from the side of the engine block, just next to the oil filter. Replace it, and you'll magically see more oil pressure. (They read low as they tire out, or at least that's been my experience.) BTW, before you reinstall these things, be sure to clean all the old gasket material off the thermostat housing, and wrap the oil pressure sender threads with teflon tape (available at the auto parts store or your local hardware store).

Keep a positive attitude! You can do it! Girl power!

[cozye]

True that the temp in the radiator could be cooler. My thought is that the water circulates while running, so if you do it as soon as you stop driving it should be fairly close. It shouldn't be any hotter than the water temp sending unit, so if the thermometer says 170, and the water temp gauge says 140, you know that the gauge is wrong. Of course if it reads cooler than the water temp gauge, you haven't proven anything.

[FastWoman]

Hmmmm... Well, it depends on where it's measured. I suppose if you measure at the top of the radiator (where the water returns from the engine), that's probably true.

Another way to check for a stuck thermostat might be to monitor the radiator water as the engine is warmed up from cold to warm. If the temp starts climbing immediately, when the engine starts running, then the thermostat is open. If the thermostat is operating normally, there shouldn't be any water flow through the radiator until the engine warms to its normal set point, at which time the thermostat will open, and hot water will flow into the radiator.

[Jennys280Z]

Wow there's some good ideas I wouldn't have thought of. I don't have a cooking thermometer handy...yet. Since the thermostat is just labor intensive despite being no cost issue parts-wise I suppose it's worth some troubleshooting up front.

I haven't ordered the tap and die set either yet so more tools and parts to come! A few of the above points I did address yesterday. I pulled the cover off the AFM, manipulated it gently to make sure it wasn't stuck, cleaned the potentiometer. Like last year, it seems impossible to unplug the connector underneath without taking the AFM pretty much all the way off. I can't even begin to see where that clip is or how I have to work it to unplug it.

Here's the video I promised. It shows how badly the car is running if you listen carefully. Especially at 35 seconds, it runs badly like that no matter how much throttle is applied. I gave it a hard romp in 1st gear up to about 4000RPM yesterday and it was just as bad as it always is under any load/engine speed which would certainly rule out vacuum as my gauge so eloquently taught me. It's kinda hard to see the vacuum gauge in the video but it's sitting right on 13inHg before I revved. It took me a while here to figure out how to compress/upload the video myself but I did it!

I forgot to mention last night, I heard another curious noise from the inside of the car I never heard before. It was a loud buzzing sound coming from the rear of the vehicle while I was sitting in it with the engine running at idle. I looked over my right shoulder (as if I was going to see something ) and the only thing I could think of is the fuel pump. So I got out real fast and ran around to the back and got real close to the fuel pump and saw/heard nothing unusual. By the time I got back in the car the sound went away. I am not sure this is the same sound I sometimes hear when I first turn the ignition on...it would have to be a much louder sound to hear it over the noise from the engine. But in any case, I've never heard a buzz like that with the engine on, and so because of this, I now add the fuel pump to the list of suspects of what's wrong with my car. Of course the fuel pressure test will be more important than ever when I get the gauge put in. I splurged and bought an Aeromotive 0-100 psi air-filled gauge for $30 along with the fitting that cozye suggested. Maybe you guys can help determine if the way the car sounds could point to a fuel problem. If I'm getting too little fuel plus too much air from vacuum issues that would certainly cause a lean mixture (and the lack of power and smoothness I'm experiencing). With the ignition testing I did yesterday on the plug wires and the fine shape I know my plugs to be in, I just don't have the heart to start pulling plugs today before the fuel pressure checks next weekend.

http://www.youtube.com/watch?v=sKeyr6ICVcQ

A huge new question I will be in anyone's debt who can answer...the Z has these semi-sphere rubber plugs in various places, like underneath my ignition coil, and as I noticed yesterday on my fuel pump. I've tugged on them before but don't want to pull too hard because I don't know how they come off. Maybe there's a trick to take them off right and I don't want to break anything. Or maybe they don't come off at all! But I would love to get under those round rubber caps and clean whatever connectors are under them if you guys could reassure me how to remove them that'd be awesome!

PS It seems like the best way to find parts for these cars is to shop around (so it's not JUST for fun!) because every source seems to have the best price for something. ex. I paid $209 for a new master cylinder last year and I see Black Dragon has them for $100. But some of their other parts are very out of line compared to other sources. Take for instance their '75-76 $499 bumper shock absorbers! Ouch!

So my potential purchase list so far (including recently):

Fuel pressure gauge and fitting

Fuel hose and clamps

Thermostat and gaskets

Tap and dies

Thermometer

Brake booster

Anyhoo, my gut is telling me it's the fuel pump. Yes I know my manuals tell me that newbies always assume it's a fuel delivery problem and ignore ignition but I haven't ignored ignition and tried to focus on that first...

xx