2013 Yukon XL Denali Stuck Lifter & One Clean Cylinder

[JohnsonSteven]

Hi all.  New to the forum.  I joined because of the wealth of information pertaining to the stuck AFM lifter issue on the L94 6.2l.  

 

While idling through a parking lot Friday, my engine started ticking, and quickly became a loud banging.  I made it home (approx. 8mi) with good oil pressure and normal coolant temp.  Upon disassembly, found the #4 exhaust lifter (AFM) stuck.  Cam looks beautiful still.  Vlom filter has been replaced within the last 6 months.

 

I have new lifters (all 16), GM lifter guides, valve lifter oil manifold, gaskets and bolts on the way.  

 

My question here is about the oddly clean #4 cylinder.  See pic.  All other pistons/cylinders have some carbon build up.  But the cylinder with the bad lifter is super shiny and clean.  Does anybody have any thoughts on why this would be?

 

For what it's worth, most of the valve lifter oil manifold bolts were barely finger tight.  No obd2 codes. The car seemed to drive properly before the lifter issue, with an occasional minor hesitation when first accelerating from a stop.  No oil consumption..

 

Any help would be greatly appreciated. 

[Supreme Pizza]

The only thing I can add right now, is that if your valley pan bolts are loose, then you will lose oil pressure to the AFM lifter locking pins, which will cause the lifter to fail. As far as the cylinder being clean, I would assume that the un-burnt fuel is "washing" the crud away in the non-firing cylinder.

[Supreme Pizza]

Oh, and I would only replace the 1 bad lifter. Not all of the lifters. Many lifters are bad from the factory. If the other 15 work good, keep them on the job. Then I would de-program the AFM from the ECU ($50) or use an OBD2 AFM disabler ($100), and plug the oil port that supplies oil to the AFM valley solenoids.

[shakenfake]

Hell no replace all 16 while you have it out lmao 

 

Are you doing an AFM delete cause you should.

 

My only thought on that one cylinder being squeaky clean in comparison is maybe some water got in there and cleaned the carbon off. Does the head have any markings on it like it made contact with it? That would take the carbon off.

[Jsdirt]

Yeah, I'd be doing an AFM delete ... or at the bare minimum, replacing all 16 with an aftermarket brand of good quality, unlike the junk GM stuck us all with.

 

Usually a clean cylinder is from fuel washing, or a blown head gasket. Coolant & water is an excellent decarbonizer.

[JohnsonSteven]

Thanks a ton for the input!  Things are all put back together, properly torqued and running.  I did all new lifters and kept the AFM.  I figured if the factory setup made it 200k + miles, hopefully the new lifters etc will make it close to that again.  

 

Couple of notes on the reassembly...  First, the tty head bolts were a little tricky.  The new bolts came pre-locktighted.  Threads were cleaned in the block.  Initial torque of 22lbs was barely enough to seat some of the bolts.  No, I didn't cross thread any of them...  So with 90deg for round two, and 70deg for round three, I could feel a tremendous difference in torque needed to get the last 70 degrees.  Some felt obsurdly tight, and others not so much.  With that said, they didn't all get the same degrees of torque.  Ultimately, I am confident that all were torqued enough, and a few didn't get all of the last 70 degrees.  Any advice on that for next time?

 

Second, it took about three full minutes for all the lifters to pump up to quiet.  With great oil pressure...  That had me pretty scared!  Once quiet, they have stayed quiet.  I have a few hundred miles on it now, running flawlessly.  Any thoughts on all that?

 

Thanks again to those who helped!!

[Supreme Pizza]

I just did a similar repair. For the factory lock tight on the TTY bolts, I like to remove that with a bench grinder wire wheel, and add liquid threadlocker. It provides the needed lubrication for even clamping force, while retaining the effectiveness of the locktite. That way you get good even torque them all. It sounds like you may have had some of the bolts getting gummed up with the factory stuff. Hopefully that doesn't cause problems in the future. TTY bolts are designed specifically to give even clamping pressure across the board. If they are not even, it could be problematic. You could also put engine oil on the factory bolts, so that the locktite doesn't bind up the bolt during tightening. I'm sure others will have opinions on this matter. I researched the hell out of it before I did my first one.

[Supreme Pizza]

As for the oil pressure - that is one of the major causes of lifter failures. If your oil pressure is not sufficient during the lifter mode change, it can cause the locking pin to hang up, and then the lifter is toast. The oil pump pickup tube O-ring is one of several things that could cause intermittent reduction of oil pressure, resulting in lifter failure. I recommend replacing the lifter with the stock parts, but then disable the AFM by using programming or an OBD2 port plug. Since the AFM normally fails during the mode change, then all you have to do is eliminate the mode change, which is cheap and easy to do. There are many stories online of people that did the same repair as you, just to have the lifter fail a week or two later. Lifter failure is not a cause of the problem, its a symptom of another problem. You need to disable the system or fix the original problem or you may wind up doing the job over again.