Cliffnotes:
Popped a P300 and P301
Took it in and they replaced the plug and coil pack
Was fine for a while but now it's doing it again, but not sure if it's the same cylinder as before yet.



A while back I had a misfire CEL flash at me and a few days later come back on solid. It would stumble in low RPM and/or low throttle (650-750psi fuel pressure). I checked the code and I had a general misfire (P300) and misfire on cylinder 1 (P301) codes.

I took it in under warranty and they traced the possible cause to a spark plug and/or coil pack and supposedly replaced both. The car has run fine for several weeks now and as of recently popped the solid CEL again. Not having access to a code reader and being busy with work, I had OnStar run the CEL for codes on my way to lunch today. It was hard to understand exactly what he was telling me it was, but I got out of him that it's a misfire code of some sort. The car hasn't been stumbling at all recently, so it must not be a consistant one at least.

I'm left with wondering what it could be still. Being that I'm tuned, and tuned TCs are known for eating plugs, I'm wondering if it's one of the other plugs now possibly or maybe something valve related and the plug+coil pack swap fixed only part of the issue.

Causes of misfires to my knowledge:
Bad/foiled plugs
Coil pack going out
Injector issue/clogged injector
Valve/cam issue
Bad gas/water in gas/fuel tank pump or filter issue

If it ends up being cylinder 1 again, then two causes are already weeded out. Are there any other causes that it could be that I'm overlooking?

 

Why yes Stamina, it could be your friggin piston ring biting it.

https://www.cobaltss.net/forums/2-0l-lnf-performance-tech-153/piston-ring-failure-lots-pics-inside-lnf-196631/

Was digging around and just stumbled upon my own thread again... oh to know then what I know now...

 

 

Hey, someone found an answer to their question on .net !