Pontiac Repair: po300, head gasket, spring weather

Question
1999 5.7l yukon 180,000 mi I blew a headgasket,and had the heads reworked and replaced all the gaskets. The sparkplugs on cylinder 4,6,&7 have a dry sooty deposit on them ,and the engine misses.Could it be a crossfire problem.

Answer
Hey Chuck:

Well it can be a lot of different things. a p0300 is a random misfire not a definitive cylinder that is dead or misfiring consistanly. on that engine the didtributor cars were noted for misfire conditions especially in damp "spring" weather. you could have an ignition coil starting to go bad. It could be a lot of things. withe 180K it could be just about anything! what you need is a scan tool and look at the mifire data on the engine computer to see is any cylinder seems to be more apt to misfire than another. the deposit on the plugs could be oil if the engine was severly overheated when the head gasket blew it could have damaged the cylinder walls from the intense heat. I'd do a comprssion test and see if any cylinder is low. You could have an engine sensor that's going bad and causing the engine fule mixture to be off and it's causing a misfire. again a scan tool would help out in trying to find this issue.
good luck :}