2013 Yukon Engine Knock...

Hi friends. 2013 GMC Yukon XL Denali 6.2L V8. I recently had a check engine light for a misfire on cylinder 6, and could very much feel the misfire. Changed the coil, no fix. Changed the spark plug, all is well! 3 days later, I have this engine knock happening. No check engine light, however! Pretty obvious power loss right around 30mph. Am I about to need a new motor? Why would the check engine light NOT come on with this happening?
Video of knock at the youtube link. First part is stationary, second half of the video is driving. Minute and half long.


Thanks for anyone's help.

It's a bad lifter. You won't need a new motor but you have a decision to make such as just repairing the failed lifter like for like or deleting the failure prone AFM lifters in the motor. Tons of info on these fourms of multiple different approaches you can take. Obviously you need to have this verified with some troubleshooting but pretty sure it's gonna be a failed lifter.

yep.. that's not good sounding.

who much of a diy mechanic are you? might be worth pulling a valve cover to inspect for spring or push rod. is afm active? what did the plug look like you took out and what does it look like now?

all that's more of a curiosity and many confirm what it is sounds like it is by ruling a few other things out.

afm was still active?

I concur on the bad lifter. 3 options:

1. Put some seafoam, ATF, or Marvel Mystery Oil in the crankcase (probably about 1/2 -1 quart). Let the truck idle with that in there and see if it quiets down. If it doesn't, once it's warm you can take it out and drive it fairly hard to see if the increased pressure pumps it back up and makes it work again. These lifters hate dirty oil and low oil pressure. I've had good luck over the years with this routine....aka The Tennessee Tune-up.

2. Replace all lifters with new OEM stuff and replace all oil seals for VLOM, oil pump pickup tube, and oil pressure sender while at it. Then drive again and keep oil changes at 5k or below.

3. Research the AFM delete in this site for names, etc and plan to spend more, but have a trouble free setup from there on out.

I would weigh the following before making my decision:
1. Condition of truck (rusty, beat up, etc)
2. Miles on truck and any major repairs that have/have not been done.
3. How has it been maintained up to this point.
4. Your financial situation

@j91z28d1 has a good option before jumpingto conclusions. A good visual of that engine bank without the VC on will tell you a lot.

@jmo2610 That's almost certainly a lifter failure. Time to stop running it and work on tearing the motor apart to find the cause of the problem. You could try to free the lifter but the problem will come back, it's best to replace all those worn parts with fresh non-AFM parts.

I would stop driving it period until you fix it otherwise it just gets more expensive by the mile....

Well this is... challenging news, to say the least. Dropped it at the in-laws so that I could borrow one of their cars. Looks like I've got a full slate of YouTube videos to watch to determine if this is in my scope of skill level. Gross.

Thanks for all the tips. I'm sure I'll be back soon with questions.

So I actually just picked up a 2013 Yukon xl 5.3 with a misfire on cyl 6 and same tapping noise. Super clean truck. Planning to do full afm delete with ls7 lifters, cam , etc. if you’ve done valve cover gaskets spark plugs or a water pump you can probably do this yourself. That’s my plan.

BigDogYJ said:

So I actually just picked up a 2013 Yukon xl 5.3 with a misfire on cyl 6 and same tapping noise. Super clean truck. Planning to do full afm delete with ls7 lifters, cam , etc. if you’ve done valve cover gaskets spark plugs or a water pump you can probably do this yourself. That’s my plan.

Click to expand...

I've done a water pump and spark plugs. Never done valve cover gaskets.