2002 GMC Yukon Repair Question
Mileage: 175,000 miles.
2002 GMC Denali is throwing a PO300 code after replacing Plugs and Wires
Asked by Oldhammer47Answer
So no codes or issues before the plugs and wires you said?Its strange that changing the plugs and wires caused a random missfire not a certain cylinder missfire.Your checked to make sure you didnt close or change the gap of of the plugs?Also checked to make sure non of the plugs got cracked?
Yes, We checked them when I purchased them originally, then I checked them again when I removed them this past weekend and took them to NAPA for the second time to verify the gap was correct and that none of them were cracked, just to verify that I wasnt seeing things.
All the wires are routed correctly?I have seen a lot of clogged injectors cause random miss fires there are even bulletins for that.But you said no issues before changing the wires and plugs.So what made you change the wires and plugs?I could see the plugs for maintance but i never change the wires till they fail.
Why wait for disaster, trucks running great and you want to keep it running great! The Plugs and wires had 120k miles on them which i believe is double thier life expectancy. I thought I included this statement but after readin and need to add that a flashing Service engine light comes around a constant cruse at 65mph. I am thinking of going back to the AC Platiniums.
Bad wires i really wouldnt call diaster i belive in changing parts when they go bad.I got 200,000 miles out of the spark plug wires on my car before i had to change them.If your getting a flashing check engine light that means its a major missfire that can damage the cat.So if all this started from changing the wires and plugs then iam stumped if the plugs are gapped correctly not cracked the wires are good routed correctly.I cant think of what else is going on your down to those two things.Your truck came stock with iriduim plugs so going to the platnuims unless there was bad plugs i dont know how that would help.Are you sure you only have the P0300 code?Also at night have you tried spraying the spark plug wires with a water bottle looking for sparks?Also is the missing worse with the ac on?
Honestly, I had a service mechanic look at it, while it was throwing the Code, and he too is stumped because the Truck shows no phisical signs of missfiring. It idles Great no visable misfires. Napa guys came out and also no visable misfires. There only suggestion was to take it to GM and let them play with it on a dyno machine to hopefuly detect the issue.
So you cant actually feel the missfire?Even with the check engine light flashing?
That makes things even more puzzling i would try to make it set a missfire code while watching the ignition spikes on a scope.To rule out a missfire due to a ignition fault if it were my car and couldnt make it set the code with the scope on it.I would try cleaning the injectors by running it off the pressurized canister running the engine off injector cleaner.Also put some cheveron techroline the good stuff injector clean in the gas tank.Like the gm bulletins say to do for random missfires that arent caused by plugs wires etc.