6.2 liter GM with bent spark plug

50

Asked by Northman 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.

20 Answers

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

3 people found this helpful.
30,395

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

1 people found this helpful.
50

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?

1 people found this helpful.

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?

3 people found this helpful.
50

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

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

2 people found this helpful.
157,115

Is the spark plug the correct part for the vehicle?

2 people found this helpful.
157,115

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?

1 people found this helpful.
50

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

1 people found this helpful.

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/

1 people found this helpful.
157,115

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.

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.

What was the outcome of fixing it, pls if you have time need more info 3058968674 I'm having same problem out of no were traction light and engine light came on and code reads number 7 thanks Damian

10

I have a 2013 Yukon Denali XL with the L98 6.2 liter engine. I am having the same issues as well. The stabilitrack traction control lights came on and it runs really sluggish compared to Normal... It also threw an engine code that I haven’t read yet. I know that these engines require DEXOS oil which I didn’t use last time I changed it so I’ve changed the oil with Mobil 1 DEXOS 5W30 oil and added two quarts of Lucas Oil Stabilizer. Drove it afterward and got engine to Normal operating temperature and still does the same thing.

1 people found this helpful.
50

My issue ended up being a problem with the pistons (although the actual root cause is uncertain...maybe detonation or other ignition issues). Family member is an auto machinist so we removed the engine and rebuilt it. The piston started to deteriorate and pieces would rattle around in the cylinder and eventually blow out the exhaust (sometimes causing damage to spark plug). There were 2 pistons doing this. We found damage to the cylinder and the exhaust valves. Here is the list of work done: bored and honed block to thirty thousands, replaced Pistons and rings, ground valves, replaced one bent exhaust valve, replaced camshaft, replaced lifters. Resurfaced heads and exhaust manifolds. Ground crankshaft. As well as new bearings, seals, etc. In short it was a big job, about $1,000 in parts, but I worked on it with him so no labor. Have about 80,000 miles since rebuild with no issues or engine lights at all. Mine was an extreme case, but I knew that possibility when I purchased it as the worst case would be a rebuild.

2 people found this helpful.

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