85 eta rough misfire black soot from exhaust

[2.5-12]

I did a ton of maintenance items on this car last summer, it ran alright before it, but now it is just being an a-hole.

parts serviced
distro cap
distro rotor
plug wires
plugs
flywheel, clutch and pp
intake boot
full 325i header back exhaust system
(DME is and was chipped)
changed intake manifold
changed throttle body
changed TPS
intake manifold gasket
ICV plug gasket
hose clamps on everything
injector o-rings

I have since tried:
swapping ICVs
swapping green idle boxes
swapping DMEs
swapping AFM and barometric sensors
swapping coils
swapping plug wires
swapping cap and rotor


symptoms
car will start (after a fair bit of cranking.) will idle rough and low (now idles semi-smooth at about 900rpm), when the gas is stabbed briefly, it revs up normally like an eta should nice and strong, but if the pedal is pressed only slightly the car runs even rougher and eventually will stall. when this happens, the exhaust has black soot that comes out (snow bank behind car is stained black).

the car drives, when on the gas or off the gas its ok, but partial throttle it jerks violently.

things I have read about that I should double check
cold start injector (car runs the same with or without idle at 900rpm)
test fuel pressure (tested within spec)
test compression (less inclined since car ran fine before)


ideas? I have a lot of experience with ETAs, but this one has been a bigger PITA than most.

[2.5-12]

here's an old video of it.

http://www.youtube.com/watch?v=0K0WiD4uuVc

http://www.youtube.com/watch?v=gfT4Ofr16xA

[jlevie]

One thing not mentioned in your list of things to check is to have a shop run a smoke test to look for intake leaks.

[2.5-12]

I will add it to the list, but the car ran perfectly before these maintenance items, and I didn't remove the intake in the process

[dnguyen1963]

Whenever you work on a 20+ yrs engine, you will undoubtedly jar something loose. Have a smoke test done to find the vacuum leaks. Vacuum leaks can come from many other places beside the intake boot.

[2.5-12]

while this is true, I doubt it would cause the highly rich fuel mixture.

[dnguyen1963]

I listened to your video. I still think you have vacuum leaks. It is worthwhile to look at the injectors to make sure that they are not leaky. Have you removed the spark plugs to see if they are fouled? For troubleshooting E30, it is best to eliminate vacuum leaks before doing anything else.

[2.5-12]

ok, lets move on to what I should check besides vacuum leak

it isn't a vacuum leak, I know them well in M20s and this has a different set of behavior.

I will check injectors for impedance and operation with a stethescope

beyond that -- remember it is running filthy pig rich.. sticking cold start injector, improperly flowing fuel injector

I will remove the plugs to see if they are fouled, and to check the gap. probably remove the disto cap again to check and make sure nothing is screwed up there.


anything else to check?

[jlevie]

while this is true, I doubt it would cause the highly rich fuel mixture.

Intake leaks can lean out the mixture to the point that the engine is misfiring, which will result in there being partially burned and unburned fuel in the exhaust. Which will look like the engine has too rich a mixture.

[2.5-12]

I'll smoke test the intake to appease you guys.

anything else in the mean time potentially problematic?

[dnguyen1963]

Not to appease me, but I would be happy if you can get your E30 going again. You might also want to check the ignition coil. A weak coil might not give out a strong spark resulting in rich running condition.

[2.5-12]

I have swapped coils, but I should try another just in case

my winter car is a perfect running eta as well, so I will probably take parts and swap on that to see just because they are known working.

I have a ghetto intake smoker made from a DJ fog machine and some very high temp rated hose, I will smoke test it for giggles. (kinda hope you guys are right on an intake leak coming form nowhere, would be cheap and easy to remmedy)

one thing I just thought of... TPS?

[dnguyen1963]

I have a similar setup. The output of the fog machine goes into a large enclosed tub. I then use an aquarium pump to pump the smoke into the engine. The small pump is perfect to keep the pressure at about 4 psi. Don't forget to plug the exhaust and intake.

[2.5-12]

so tested fuel pressure at 27psi, but when I removed the vacuum line to the FPR I got a perfect 37psi..

in the video, the fuel pressure spikes when I hit the throttle -- is that normal?

patched the fuel leak and it runs a lot better, attached another video, found a crack in the intake manifold, but its not letting air in.

...havent smoke tested it just yet...

https://www.youtube.com/watch?v=gf9Or2M2Ngs

[2.5-12]

So, I think that's it for this weekend. I am going to swap the TPS and the 3-4 sensors on the thermostat housing to see if that makes any difference.

(Forgot my smoke machine downtown, derp)

Fuel pressure and fpr behavior are apparently normal, so that's good.