Mechanics

MISFIRE

2002 GMC Yukon

Engine Performance problem
2002 GMC Yukon V8 All Wheel Drive Automatic 56,546 miles

took my truck to the gmc dealer for adiagnosis of a lack of power. The truck seemed to run good at an idle but lugged when I got on the throttle. I was told that it was missing on number six and it was either a broken valve spring or a fuel injector. At this point I took the truck home and did some looking.

-pulled off the valve cover, springs ok -changed fuel injector, no change -did a compression test, 150psi -did a compression test with both ajacent plugs removed, 150psi -moved plug, lead, and coil to different hole, no change -tested fuel pressure, ok -tested with noid lights, ok -sprayed intake while running with cleaner found no vacum leaks. Please help
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Norunyukon
January 12, 2009.




What about intake gasket failure on the valley side?

Docfixit
Jan 13, 2009.
Installed new intake manifold, still no change

Tiny
Norunyukon
Jan 16, 2009.
This may sound weird but pull valve cover rotate engine see if intake valve is opening.
AD

Docfixit
Jan 16, 2009.
Pulled off the valve cover just now and all the valves are moving the same

Tiny
Norunyukon
Jan 19, 2009.
There is a service bulletin on any missfire 301 to 308. Look for ground wire either on front or rear of right cylinder head. Remove clean see what happens.
You now know it is none of the stuff Dealer told you.

Docfixit
Jan 19, 2009.
Looked all over both front and back of heads, I found no ground wire or any markings of one that may have been. There is however one large ground that goes from the firewall to the block, cleaned no change. Also to note did a leakage test, like new.

Tiny
Norunyukon
Jan 21, 2009.
Is this a plain Yukon or Denali or what. Is it 4.8 5.3. Or 6.0?

Docfixit
Jan 21, 2009.
I am sorry that I neglected to add that into the description. Yes it is the denali with a 6.0l

Tiny
Norunyukon
Jan 21, 2009.
O.K. That helps there are a few TSB on the fuel system what I need now is the DTC in the P0xxx format. When you did compression test where all plugs out? If not that will not give a reliable reading.

Docfixit
Jan 22, 2009.
The code it gives is P0300, when I did the compression test I removed all the plugs.

Tiny
Norunyukon
Jan 22, 2009.

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