Thread: Misfire Misery
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Old 06-10-2021, 12:57 PM
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Quote:
Originally Posted by Briansbummerbmw View Post
I was thinking it might be a broken wire in harness is why I checked with noid light. But maybe more info a about the moment misfire started and some backstory. The car always had quite a bit of blow by out of oil filler hole but ran pretty good. I filled up an almost empty tank with gas, and was on the freeway for about 30 miles at about 70 miles when I felt a miss. Then in about a half mile later another and I was sure something was, so exited freeway and at red light was loping bad. I made it to work and took a chance on plugs ans coils in hopes that was it and could get back home. Problem still there but made it back. One other thing is that serpentine belt went out on freeway about 2000 miles earlier and I got the overheat light. I had just pulled off when the light came on. I let it cool down then drove about 5 min to autoparts and changed belt in parking lot. About 2 tablespoons of coolant had o overflowed around cap. It seemed fine after that but maybe the heat damaged something that just took a while to show up. Like bent or burnt valve. Maybe unrelated. The other thing is the first time I cleared to codes it had some pep and was feeling zippy or pretty good until the moment the check engine light on, so much so that my girlfriend thought I had fixed it. The moment check engine light came on it started crapping out again. I dont know if any of this is relevant. I'm starting to just lose my mind with frustration.
Check engine light came on most likely due to misfire (count on the DME). When that happens the DME shut down the injector to the cylinder that the misfire was detected on. With the injector shut down, you lose that cylinder that is why you don't have zip. Normally shutting down the engine will reset the misfire counter and the DME will fire the injector again until that magical misfire count is reached. As for the overheating, you most likely warp the engine head and now you have a damaged head gasket. That could be the source of the low cylinder compression.

Do a leak down test to determine if you have a cylinder leak.
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