Hey all-- I am wracking my brain with this one. 2002 Yukon XL 5.3 regular fuel, 150K. I am getting the most random misfire! One day it will be on cold start and it wont go away until the engine is almost to operating temp. I have to shut it down and restart it several times. Sometimes it will clear up in a minute, other times, 20 minutes. This is NOT daily though! Then there are times where it will randomly start misfiring while I am driving. Doesn't matter the speed, RPMs, etc. Its random. I pull over, shut it down, then it will restart fine.
So far- I have new plugs/wires (it was due), new fuel pump and FPR, ran injector cleaner through, new vacuum line on EVAP, new MAF. I changed the MAF this morning- the misfire happened at start up. Turned it off, unplugged the MAF, and miss was gone. Still got a misfire while driving this afternoon.
I am running consistently lean, but not enough to set off a lean code. I am down anywhere from 15-30% on MPG, given the day.
90% of the time it runs just fine! Been through a few different mechanics. The only codes it ever throws are P0300 and on a couple of occasions P0307 (replaced that coil just to be safe).
ANY ideas and suggestions are welcomed! I do have scan data if you are interested...... thanks!!
So far- I have new plugs/wires (it was due), new fuel pump and FPR, ran injector cleaner through, new vacuum line on EVAP, new MAF. I changed the MAF this morning- the misfire happened at start up. Turned it off, unplugged the MAF, and miss was gone. Still got a misfire while driving this afternoon.
I am running consistently lean, but not enough to set off a lean code. I am down anywhere from 15-30% on MPG, given the day.
90% of the time it runs just fine! Been through a few different mechanics. The only codes it ever throws are P0300 and on a couple of occasions P0307 (replaced that coil just to be safe).
ANY ideas and suggestions are welcomed! I do have scan data if you are interested...... thanks!!
