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2002 GMC Yukon misfire

Tiny
NORUNYUKON
  • MEMBER
  • 2002 GMC YUKON
  • V8
  • AWD
  • 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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Monday, January 12th, 2009 AT 3:05 PM

19 Replies

Tiny
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What about intake gasket failure on the valley side?
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Tuesday, January 13th, 2009 AT 11:01 AM
Tiny
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Installed new intake manifold, still no change
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Friday, January 16th, 2009 AT 12:47 PM
Tiny
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This may sound weird but pull valve cover rotate engine see if intake valve is opening.
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Friday, January 16th, 2009 AT 6:32 PM
Tiny
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Pulled off the valve cover just now and all the valves are moving the same
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Monday, January 19th, 2009 AT 2:18 PM
Tiny
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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.
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Monday, January 19th, 2009 AT 5:10 PM
Tiny
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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.
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Wednesday, January 21st, 2009 AT 8:56 AM
Tiny
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Is this a plain Yukon or Denali or what. Is it 4.8 5.3. Or 6.0?
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-1
Wednesday, January 21st, 2009 AT 3:56 PM
Tiny
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I am sorry that I neglected to add that into the description. Yes it is the denali with a 6.0l
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Wednesday, January 21st, 2009 AT 4:26 PM
Tiny
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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.
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Thursday, January 22nd, 2009 AT 8:00 AM
Tiny
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The code it gives is P0300, when I did the compression test I removed all the plugs.
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Thursday, January 22nd, 2009 AT 5:41 PM
Tiny
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Hi
Just found out you replied P0300 is random cyl missfire which does not compute if miss is isolated to one cylinder. What where compression redings 150 psi or above? Let me do some research just got off work and am beat.
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Monday, February 23rd, 2009 AT 3:25 PM
Tiny
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I know it seems strange but the compression on all is 150 plus, if I run it long enough now it will show a misfire on number four althought not so severe. When I swap coils, wires etc. Clear codes and start it misses on number six only, then after a while number four starts to miss intermitently. This is new. Chased the wiring harrness as best as possible and did not see any thing out of the ordinary.
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Tuesday, February 24th, 2009 AT 8:39 AM
Tiny
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Must go back to earlier post harness ground wire. Located on right front of cylinder. As you sit in truck the right is pass side. Look on head just up from water pump it will bolt straight down into very front of head. Let me know
TSB 06-06-04-046 date 12Sept06
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Wednesday, February 25th, 2009 AT 4:26 PM
Tiny
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Finally warmed up enough to take another look.
There is no ground wire on either head, front or back
nor is there any sign that there ever was. Also to note I ordered this truck new, its never been hit and always serviced at a GM dealer.
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Wednesday, March 4th, 2009 AT 6:16 PM
Tiny
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Maybe I need to tell you harness groung G105 is a small black wire in gator flex. Attached to right front cylinder head behind water pump pully. It is ground for coils 1, 3, 5, 7. The ground for other coils is on back of left head. All GM engines have this ground from 4.8 to 6.0.
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Thursday, March 5th, 2009 AT 9:28 AM
Tiny
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Finallly got warm enough to go out and take a look again. Used lights and mirrors searched all around both heads I could not find any signs that there any wires attached. Looked around for any loose wires in loom or bare and found none. Is there a pin out on the ecu for this ground? I don't imagine that I could just run a jumper over from the battery?
Thanks
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Monday, March 23rd, 2009 AT 9:11 PM
Tiny
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Wire comes from coil pack to the engine maybe on intake directly behind water pump
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Tuesday, March 24th, 2009 AT 9:54 AM
Tiny
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Finally got a chance to get back at the unit. After checking every thing else crawled under with a home made pressure tester and found 8 psi at the right hand o2 sensor @ idle. Thought that the GM dealer would have checked this when it all started. Had it towed back to dealer at which time I was told that even if they changed the cats it would still miss. Got it back after one week, dealer changed all cats runs like a dream, no miss. This was at no charge as the catylic converters were still covered on warranty (8 years)
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Monday, June 1st, 2009 AT 11:59 AM
Tiny
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Excelent news will put that one in memory bank. Yes I would have thought backpressure would have been checked as CATS Care top of list for the code P0300.
Glad it was no charge you got in just before they went banckrupt.
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Monday, June 1st, 2009 AT 1:53 PM

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