Misfire on Cyl #4...

[Jtuner]

So I've done a few searches and scoured other sites for my exact same situation, but each one seems to deviate a bit from what's going on with my car, so i figured I'd post and pick ya'lls m42 minds and see what I can figure out..

1991 e30 318is with an m42

OK so 2-3 weeks ago, I start my car in the morning,, probly about 40-50 degrees outside,, Its starts up misfiring, I furrow my brow, hit the gas and the misfire goes away, and doesn't come back until....
Two days ago, I drive about 30 mins down to my bro's shop, and when I hit a stop light, I feel my car is misfiring again.... I pull in to his shop and start unplugging coils, and find that cyl 4 is indeed misfiring.. I immediately change out spark plugs and find condition remains.. Swapped coils and still found cyl 4 misfiring.. Now I did do the COP conversion on my car, so I tried reinstalling the entire old coil set with the same results...  I've pulled apart my coil wiring on 4, and found everything clean, pins are tight.. I even decided to pull my ecu and make sure I wasnt getting any water intrusion or if my EEPROM chip was loose, and everything seems fine...

So I know this much --> Cylinder 4 is misfiring --> Its not a coil --> Its not a spark plug --> There is no fault code being thrown from the code check --> from the way my cat is smoking and turning bright red, I think its safe to say its not an injector --> injector is not leaking...

That's about it.. I've seen that some people with a similar issue have had a crank sensor problem, others, it was a coil or spark plug fouled.. some suggested tps or maf,, One person on here that had the closest to my problem had a misfire condition on coils 2 and 4, and replaced the ECM due to it never sending out the 'fire' signal to those 2 coils...
I haven't attacked with my ohm meter yet, but I kinda wanna have a plan of attack before I start unplugging my brittle old connectors....

Any input would be WONDERFUL, this car is my main mode of transportation and needs to be back on the road asap!! Thanks ya'll

[B318M42W]

did you try a compression test? If your cat is getting really red, I'd think that you got a busted exhaust valve. And an easy test you can do is to take all the plugs out and connect the plug wire with a plug and then ground the plug. (testing if it sparks ok/strong/weak/not at all).


But just to make sure, when you say misfire, is it that it DOES NOT fire at all or it fires not at the right time?

[Jtuner]

ah yes, I have done the spark plug on the end of the coil test, and found no spark at all.. by misfire I mean, not firing at all,, no spark, just fuel injector pumpin gas in there lol I have not done a compression test yet, but I may check that avenue,, i think my bro has a comp. tester...

[kowalski]

I had the same problem.
I did the same things you did, but i bought 4 new coils with my cop kit. Fixed my problem, turns out more then 1 coil was cookd.

[Jtuner]

Yeah, temp gun says the only cyl out is 4,,, I'm ordering a new ecu today or tomorrow,, I hate to shotgun, but everything else seems to be working... I'll let ya know what happens lol

[Jtuner]

It ended up being an ECM afterall,, its the only thing that really made sense.. Thanks for the help anyways

[B318M42W]

glad you found your problem!