Hey guys,
New here to the group. Just received my HPTuners suite to use on my 06 GTO LS2 M6 I have some experience on older cars, the last tune I did was on an 89 Firebird Formula 350 with TPI (obviously, that tune was a bit simpler than what is in the newer cars).
I am having what I consider a pretty weird situation. Car ran great and had no issues, started getting a lot of vibration and found a bad engine mount. I changed the mounts for polyurethane engine and trans mount. I also changed the starter while working on the car to solve a hot start issue with weak starter. Shortly after getting it back on the road, I started getting random misfires and CEL with code P0300. All 8 cylinders see misfires and none seem to have a statistically higher count than the others. It only seems to happen after highway cruises. If I drive the 60 miles to work, CEL will come on halfway home. Sometimes it may take it a day or two, but it will reliably come on. If I stick to round town driving, it will sometimes go back out after a few on/off cycles.
Admittedly, I threw some parts at it assuming it was something simple. Here is the list of changed parts/procedures:
Plugs/wires
Upstream O2 Sensors
Cleaned fuel injection system (OTC tool with Pro Inject-R Kleen)
Checked fuel pressure
Smoke tested intake tract looking for vacuum leaks, none found
Changed Crank sensor and did a relearn (banged against it a number of times taking the starter in and out)
Cleaned MAF
Had dealer perform top End clean as per TSB
I have not data logged the car yet, but will get a few logs starting tomorrow to work and back.
Anybody have any ideas? I cannot see why Poly engine mounts would cause a misfire but unless the timing was pure coincidence, that is all that changed.
Thanks in advance for any advice,
Drew.