What next?!

[FastWoman]

Hi all,

Here's my predicament: I'm still going through the fuel/intake system of my '78 Z to get everything running right, but I have quite a few items to go. It seems everytime I replace or clean up a connection, the engine runs differently -- sometimes better, sometimes worse -- sometimes richer, sometimes leaner. (Sounds like marriage vows.)

I'm now at a point where the engine runs great on startup, but it gets rough when it warms up. The exhaust is sooty, the plugs are all equally sooty (and not oily). The exhaust blows pretty hard in forceful puffs.

I wanted to verify that the engine needed a leaner mixture to run better, so I cracked the oil filler cap to introduce a bit of air beyond the air flow meter. I expected RPMs to pick up, but they did not. No matter how small or large an amount of air I introduced that way, it only diminished the idle and made the engine run rougher. I also did the same thing by opening a small vacuum line, with the same result.

I'm confused that I can have sooty, rich-smelling exhaust and not have engine function improved by introducing "extra" air into the intake manifold. How could this be?

I know my water temp sensor is inaccurate. The resistance reads somewhat high, and that would result in too rich a mixture. I don't know how big a factor this would be or whether my next step should be to replace it. BTW, someone had previously wired a resistor in series to enrichen the fuel/air mixture. I removed the resistor, and that did lean the mixture a bit (returning it a bit more towards normal).

My injectors are also old. I have a new set on rail ready to mount up. I believe my old injectors are probably performing uniformly from cylinder to cylinder, as all my plugs look the same (sooty). Do old injectors generally inject too little fuel (from being clogged with deposits) or too much fuel (from having worn passages/parts)? I know my fuel pressure is regulating a few PSI too low as well. The regulator on the "new" fuel rail regulates at a more normal pressure, which of course would enrichen the mixture relative to the pressure regulator I have.

It's easy, BTW, just to say to do these things and see what happens, but I want to tackle these jobs in an order that will keep my engine operable. That will make it easier to determine what the problem is (because a non-running engine is hard to diagnose), and it will keep my car mobile, in the event one of these hurricanes causes flooding where I live. (My car is parked at 6 ft above mean low water level.)

Diagnostic steps taken:

The valve lash is in correct adjustment, and valve timing is within specs. The cam sprocket is mounted on the #1 hole (engine has >160k miles on it), and the mark on the sprocket aligns just even with the oblong mark on the plate behind it when the engine is TDC. Engine vacuum is very low (maybe 14), but that would simply indicate inefficient running, which I already know.

Distributor is timed at 10 deg BTDC, per factory specs. I think the engine "wants" more advance.

Diagnostic steps not yet taken:

Compression test. (Can't find my tester! Grrrr)

Various electrical measurements on the EFI, per the FSM.

I'm basically trying to get the hardware correct and in place, get all my electrical connections good (all done now, except for on the injectors), and then diagnose other issues from the EFI connector, ultimately maybe adjusting the AFM to fine-tune the fuel/air mixture.

Any thoughts as to how I should proceed from here? Most of all, any insights as to how I can have rough idling and sooty, rich-smelling exhaust and NOT improve the idle by introducing extra air into the intake manifold?

Thanks for your advice!

Sarah

[jonathanrussell]

I would start by....

- replace your water temp sensor since you know it is bad.

- make sure you haven't crossed up your thermaltime and temp sensor harness.

- the most fuel rich my 75 280 has ever run was when the AFM flap was stuck open. You might check that.

- any chance your cold start valve is spewing?

Other than that, I would say you need to start methodically testing your efi via fsm.

As to why you are not seeing improvements when you introduce unmetered air via vacuum leak....not sure unless you just have not introduced enough unmetered air to overcome the over rich condition.

Seems like I have followed other recent work you have done- ie: installing header. Are you sure you are rich? Are you sure you don't have a massive intake manifold gasket leak?

Best of luck.

j

[MK1888]

Your Z has Bosch engine management, right? I've had VWs with Bosch and they had a default super-rich mode when the O2 sensor was bad. I had to circumvent it a couple times in order to get home by disconnecting the coolant temp sensor, which simulated a startup condition and ignored the O2 sensor.

I don't even know...Did they have O2 sensors in 1978?

Mike

[FastWoman]

Hi Jonathan,

Thanks for your input/suggestions!

I can't say I'm sure of many things, but I'm nailing down issues one by one.

Thinking about the mixed rich/lean symtoms, I started wondering whether my injectors are sticking, such that cylinders occasionally get a pretty rich charge of fuel and are otherwise running lean. In other words, I'm wondering whether the fuel delivery is random and inconsistent from pulse to pulse. Another possibility is that the injectors are running fuel and not atomizing it, so that the burn is very inefficient, leaving lots of unburnt hydrocarbons and symptoms of a lean mixture. (Is that possible?) Anyway, I went ahead and started replacement on the injectors and their connectors. I beat a retreat when the mosquitos started attacking, but I should know more tomorrow.

Water temp sensor would be next.

I'm positive the thermatime and temp sensor connectors aren't switched. It's kinda dumb for them to have put the same sorts of connectors in such close proximity. I labeled the temp sensor connector "temp" just to be certain I don't mess up. It's traced all the way back into the engine harness (which I wired with the new connector), so I know it's correct. (I was very methodical and worked connector by connector, checking, double checking, etc.)

Stuck AFM flap? Yow! Hadn't thought of something like that. I'll definitely check that out. Thanks!

Cold start valve? Maybe.

Massive manifold leak? I wouldn't rule it out. Is there a good way to test for that, not involving introduction of something flammable near the suspected leak? (Remember, I have a leaking exhaust too!) If the manifold is leaking, it will soon be corrected anyway, as I'll be replacing the intake/exhaust gasket.

Edited September 20, 2010 by FastWoman

[jonathanrussell]

When my intake manifold gasket was leaking, I finally figured out that I could hear it. Of course, a vacuum gauge showed low and sporadic vacuum readings also. Supposedly, you can spray starter fluid on an intake leak and your engine performance will immediately, temporarily improve because the fluid gets sucked in and corrects the lean mixture condition. I never tried this though because I could hear the leak and knew I had to r&r the intake/exhaust/gasket etc.

I am sure you know but you can identify the thermatime harness by virtue of the fact that its harness wires will have continuity with the cold start valve harness wires.

It will be interesting to read what solves it.

j

[FastWoman]

I don't hear anything, so if I have an intake leak, it might not be all that large. Of course I know I have the exhaust leak, and it's blowing on the underside of the intake manifold. If I have an intake leak in the same area, then I might have some "extra EGR" going on. Yikes!

I'll pass on the starter fluid approach for now! Maybe after my exhaust manifold is tight.

[Pomorza]

Hi all,

Here's my predicament: I'm still going through the fuel/intake system of my '78 Z to get everything running right, but I have quite a few items to go. It seems everytime I replace or clean up a connection, the engine runs differently -- sometimes better, sometimes worse -- sometimes richer, sometimes leaner. (Sounds like marriage vows.)

I'm now at a point where the engine runs great on startup, but it gets rough when it warms up. The exhaust is sooty, the plugs are all equally sooty (and not oily). The exhaust blows pretty hard in forceful puffs.

I wanted to verify that the engine needed a leaner mixture to run better, so I cracked the oil filler cap to introduce a bit of air beyond the air flow meter. I expected RPMs to pick up, but they did not. No matter how small or large an amount of air I introduced that way, it only diminished the idle and made the engine run rougher. I also did the same thing by opening a small vacuum line, with the same result.

I'm confused that I can have sooty, rich-smelling exhaust and not have engine function improved by introducing "extra" air into the intake manifold. How could this be?

I know my water temp sensor is inaccurate. The resistance reads somewhat high, and that would result in too rich a mixture. I don't know how big a factor this would be or whether my next step should be to replace it. BTW, someone had previously wired a resistor in series to enrichen the fuel/air mixture. I removed the resistor, and that did lean the mixture a bit (returning it a bit more towards normal).

My injectors are also old. I have a new set on rail ready to mount up. I believe my old injectors are probably performing uniformly from cylinder to cylinder, as all my plugs look the same (sooty). Do old injectors generally inject too little fuel (from being clogged with deposits) or too much fuel (from having worn passages/parts)? I know my fuel pressure is regulating a few PSI too low as well. The regulator on the "new" fuel rail regulates at a more normal pressure, which of course would enrichen the mixture relative to the pressure regulator I have.

It's easy, BTW, just to say to do these things and see what happens, but I want to tackle these jobs in an order that will keep my engine operable. That will make it easier to determine what the problem is (because a non-running engine is hard to diagnose), and it will keep my car mobile, in the event one of these hurricanes causes flooding where I live. (My car is parked at 6 ft above mean low water level.)

Diagnostic steps taken:

The valve lash is in correct adjustment, and valve timing is within specs. The cam sprocket is mounted on the #1 hole (engine has >160k miles on it), and the mark on the sprocket aligns just even with the oblong mark on the plate behind it when the engine is TDC. Engine vacuum is very low (maybe 14), but that would simply indicate inefficient running, which I already know.

Distributor is timed at 10 deg BTDC, per factory specs. I think the engine "wants" more advance.

Diagnostic steps not yet taken:

Compression test. (Can't find my tester! Grrrr)

Various electrical measurements on the EFI, per the FSM.

I'm basically trying to get the hardware correct and in place, get all my electrical connections good (all done now, except for on the injectors), and then diagnose other issues from the EFI connector, ultimately maybe adjusting the AFM to fine-tune the fuel/air mixture.

Any thoughts as to how I should proceed from here? Most of all, any insights as to how I can have rough idling and sooty, rich-smelling exhaust and NOT improve the idle by introducing extra air into the intake manifold?

Thanks for your advice!

Sarah

Sarah.

A few things of note I noticed in your post. For what I remember opening the oil filter cap (or dip stick at that) causes the motor to run rough. If I'm not mistaken (I maybe) the oil cap and dip stick are there to prevent a vacuum leak. So it is natural for the engine idle to roughen when you pull these. (Or in my Z it does).

Secondly, if you have the EFI book (there's a link on the xenon page) it talks about how the computer uses the temp sensor to figure out how much fuel is needed. If this was bad, hypothetically you would no get the right mixture of fuel when needed.

Thirdly, check the little boots that go between the air filter and the AFM and from there to the intake. On my Z both of these had GIANT holes causing a very interesting engine performance. I would find my compression gauge and do the test and see where the engine is at. I'm not a car expert here by any means (I'm 22 so) but I would suspect you may just have a vacuum leak some place as your said you have low vacuum. You can try the smoke test where you introduce smoke into the vacuum system and check for leaks.

Hope that helps

Jan

[FastWoman]

Jan, thanks for reminding me about the EFI book! I had forgotten about it.

I had also forgotten the intake boots. They're quite old, possibly original. Hmmmm...

The idea behind cracking open the oil filler cap is to lean the fuel/air mixture. In YOUR engine it causes rough idling, because your fuel/air ratio is probably normal. In an engine running too rich, it should improve the idle -- or so they say. Anyway, yes, the filler cap and dipstick should seal tightly for normal operation. (Mine do.)

Wish me luck on the injectors! I won't know anything else until I complete the installation, because right now it won't run.

[Z train]

Start at the beginning.Meaning the ECM.Make sure the connections are soldered correctly.Then "run out" all the connections to their end.

http://www.classiczcars.com/forums/showthread.php?t=36903&highlight=ecm

Edited September 20, 2010 by Z train

[FastWoman]

Yikes, Ztrain! Bad solder joints are pretty rare and usually only in subpar equipment! I wouldn't expect such a thing from Hitachi (?). Well, I did pick up a spare '78 ECM a while back. It's an easy thing to try a quick swap. Thanks for that tip!

[mlc240z]

Sarah,

Not just from sub-par equipment.

Don't forget it's 32 years old. Years of hot/cold temperature cycling from daily start-up/run/cool-down can cause even 'good' solder joints to fail.

Found it on a lot TV and PC monitor circuit boards that are in climate controlled rooms all day, not out in the weather and/or subject to engine heat.

If you can pull the board and inspect the bottom with a magnifying glass, you might be able to see the separation and do a quick fix with a soldering gun to re-flow the solder.

Fixed more than a few that way.

As far as introducing a little extra air, by pulling the oil filler cap or dipstick you're affecting vacuum, not introducing air into the combustion chamber.

From what I 'know' about fuel injection, to introduce more air to the mixture you would want to create an air leak by cracking the air 'hose' AFTER the airflow is metered by the ECU.

Edited September 20, 2010 by mlc240z

[Z train]

Yikes, Ztrain! Bad solder joints are pretty rare and usually only in subpar equipment! I wouldn't expect such a thing from Hitachi (?). Well, I did pick up a spare '78 ECM a while back. It's an easy thing to try a quick swap. Thanks for that tip!

A spare is always a good idea.But you're forgetting that the location of the ECM has more to do with solder joint issues than bad equiptment.The kick panel where it is located is not only prone to "road shock& vibrations" but is also really close to the drivers door which gets opened & closed the most.

Be really interesting to see how many ECMs & fuel pump relays were replaced because of solder joint issues.

My 85 720 had a FP relay go bad and a 2 minute solder job fixed it.

Edited September 20, 2010 by Z train