6.2 liter GM with bent spark plug

10

Asked by Jun 09, 2017 at 02:07 PM about the 2007 GMC Yukon XL Denali 4WD

Question type: Maintenance & Repair

I have a GMC Yukon XL Deanli with the 6.2 liter engine.  I have a tic/knock
in the engine.  Then it started to run rough and the stabilitrack traction
control lights came on.  It also triggered a misfire code on cylinder 2.  I took
cylinder 2 spark plug out and it was bent over (see pic).  I gapped the plug
(eyeballed) with plier and tried it.  It ran fine then and the stabilitrack
traction control lights turned off, just had the knock still.  Ran that way for
1,000 miles. Then it did it again only this time the code was different
(P0300 randon/multiple misfires) and it turned out to be cylinder 8 spark
plug that was bent this time.  Somehow something is impacting the spark
plug.  Not sure if it is foreign debris or what.  I have talked to several people
about this and all are stumped.  Hope someone here can help.

16 Answers

80,015

That plug looks like it has been overheated which may be caused by detonation. Replace the plugs and try it again.

10,550

Here's a SWAG (scientific wild-ass guess) is it possible for a carbon buildup ,,, Nah,that ain't possible ... is it?

10

F_O_R, the pic I showed was when it happened the first time. It was driven that way for a bit as my wife was on a trip. The plug didn't have so much buildup the second time. Tom, that theory has been kicked around, but the thought is it wouldn't build up enough to do that?

80,015

I would install new plugs and see what happens. If you are having severe knock then the timing may be off. Are you using premium fuel?

10

That is kinda the plan at this point. I may try get a scope to borrow and try look in the cylinders through the spark plug hole to see if I can see anything. I am not using premium fuel. I know it is "recommended" on this vehicle. That is something I could try. Thanks

80,015

Using the wrong fuel and having a faulty knock sensor could cause your problem.

52,715

Is the spark plug the correct part for the vehicle?

10

Yes, spark plugs are correct

52,715

Stick a bore scope into the cylinder and look for excessive carbon deposits. Excessive carbon at the top of the piston can cause a knock and damage the spark plugs. Is this a high mileage engine that uses oil?

10

Bob, I am currently asking around to see if anyone has a bore scope I could borrow. I was Thinking debris, but will certainly look for carbon as well. It is high mileage (207,000) and it does use oil. Thanks

80,015

You can buy a bore scope cheap at Harbor Freight.

80,015

Read this article but I still think you are having detonation problems. http://www.onallcylinders.com/2012/12/20/reading-101-how-to-read- your-spark-plugs/

80,015

Try using premium fuel and go one range colder on the spark plugs.

52,715

Although I would agree with F_O_R that running premium might help, I would disagree about changing the spark plug heat range unless you know exactly what you are doing. It may be time for a Seafoam or similar treatment to get rid of excess carbon on the piston head.

Did you get it fixed?

80,015

Bob, I think it is worth a try. Going a range colder won't hurt anything at this point. If they become fouled then go back to the stock heat range.

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