Hi guys,
My car is exhibiting an intermittent hesitation and more frequent, but varying misfire condition, particularly when the engine is cold. I'm hoping someone might suggest ideas as to how I should proceed on both a troubleshooting and issue management perspective.
The car ran kind of rough. I thought it was just a crude engine. There was some intermittent light hesitation when the engine was cold. Then it had a flashing check engine light - multiple cylinder misfires. I take it into the dealer, they say plugs are fouled and they suspect bad gas. I only bought premium gas from national chains. I'm skeptical, but go with it. They drain the tank, put their own gas in and replace 6 of 8 spark plugs.
I take the car home and it begins exhibiting greater hesitation, particularly when the engine is cold, ambient temperature being a possible contributing factor. I start messing around with the torque app and start monitoring/logging GM misfire PIDs. The car is misfiring on all cylinders, particularly when cold, but there are some misfires at various times.
I make another appointment, they can only see the car a week and a half later. The car seems to run very rough a couple of days before the appointment. On the day I'm going to drop it off, the car runs horribly, I take it home and call roadside assistance. At that point I had only run gas provided by the dealership.
The dealership says residual bad gas must have caused the problem. I argue, but they say they can't find anything else. They say they tested the fuel injectors. Apparently the car had a CEL P0300 when they looked at it, that must have just turned on when they started the car. They replace 2 more fouled plugs, put in new gas and send me on my way. I pick up my car and find misfires in the parking lot prior to moving. I go back in and ask a service advisor to make a note in my file. The engine was warm at that point. More misfires occur on the way home, but it's not horrible. Later in the night after the engine cooled down, I take the car for a short drive and there are plenty of misfires on all cylinders. CEL P0430 comes on, bad cat. I write the service manager a detailed email noting this and include logged OBDII misfires.
What should I do here? I'm not sure what the problem is. I suspect the plugs are fouling due to poor running conditions. I really don't want to go back there, but I'm also out a bunch of money that warranty probably should have covered. "Bad gas" seems to be the perfect excuse - in their logic, there's no way to clear it out, even if you pay them to do it and they provide fresh gas. It's also a diagnosis of exclusion - can't find anything, must be the customer's fault. GM warranty specifically calls out a exception for damage caused by bad gas. Now that the dealership has suggested that is the problem, I may not have any recourse for escalating the issue or having warranty pay for the fix. I'm guessing the P0430/bad cat was caused by misfires and poor engine operation.
In between appointments I pulled a plug myself and it smelt like gas. I put in a fresh plug and did ~35miles on it. It was pretty black when I swapped back in the original (possibly replaced once).
How many misfires does a normal 6.2L engine typically exhibit on a given drive? Has anyone ever checked OBDII [GM] Current/historical misfires? If anyone was interested in checking their car I would be very grateful. I used the torque app and logged, but here's the custom pid details if your setup is a bit different.
[GM] Misfire Current Cyl1-4: PID 221205-221208
[GM] Misfire Current Cyl5-8: PID 2211ea-2211ed
Min value 0, max 1000, scale factor x1, unit type count, equation A, OBD header Auto.
[GM] Misfire History Cyl1-4: PID 221201-221204
[GM] Misfire History Cyl5-8: PID 2211f8-2211fb
Min 0, max 1000, scale factor x10, unit type count, equation (A<8)+B, OBD header Auto.