[RayYork]

OK, I need your input on this issues as it has even my dealer stymied. I will give the timeline of events below but the net result is that the performance of my engine varies noticeably from run to run (drive to drive, cycle to cycle, etc). It will run smooth and as expected one time and then the next it will start with a miss (my perception) and then the power will feel very flat. It never feels underpowered but a strong pull in 3rd gear from 2k (RPM) to 5k just feels labored. When this is happening my exhaust note is noticeably different as well. The exhaust note goes from the rich throaty note to something much raspier and almost has a rattle sound to it (it's hard to quantify these things....). This is a 2011 2SS/RS M6 with 56,000 miles on it. I took it into the dealership and the tech said that he agreed that it was running poorly but all systems were within GM spec so the computer thinks that all is well. He started it up today (after holding it overnight and getting a cold start) and it is running great and all systems are within spec. He cycled it again this afternoon (warm start) and it is running well and all systems are within spec. They are giving me the car back to drive for a few days and see what I think and then test it again.

OK, that's where we are today, here's what lead to this point. In February, my motor lost the oil pump check valve (I found more than one thread on this issue here so it's somewhat common). I noticed the issues right away but it did starve the engine enough that the lifters did tap at idle for a matter of seconds. After a very long and frustrating process (no need to go into here but suffice it to say that I was not working with my regular dealer and it was a mess), the pump was replaced and I was back on the road. About a week after getting my car back I was heading out to work and my DIC went nuts and my car was running like crap. the CEL was flashing so I pulled back into my driveway and had the tow truck come and pick it up and take it to my regular dealer. They discovered that when the other dealership reinstalled my water pump, they pinched some wires between the pump and block and those wires eventually shorted out and sent my motor into a tizzy. It dumped so much fuel into the #1 cylinder that it washed past my rings and into my crankcase. I just had the oil changed and 2 days later had it changed again. My dealer repaired the wiring. I cannot say for sure if it was running poorly between dealer #1 replacing the oil pump and my dealer fixing the wiring but this all started with the fateful oil pump check valve failing.

If you have any similar experiences or advice, I would appreciate it. This one has me and my dealer confused.