#5 Misfire and Lifter/Valve Noise

[Beartoothweb]

I have a 6.2L in my 2007 Denali, 208k miles.

It's been a great rig, and other than the cold start up noise that we mostly all have, no issues.

About 2000 miles ago, it started having a #5 misfire at idle, and a rough idle, bouncing around at about 485-510rpm. If I could keep it at 600rpm, no issue, no codes, nothing, all seemed fine.

Yesterday morning, I began hearing a "chirp" coming from the engine, which I thought was the idler pulley bearing failing.

Upon further inspection, it's actually coming from Cylinder #5, and my mechanic and I think it could be a lifter issue.

I don't have AFM in this rig, or at least I'm 90% sure.

I'm suspecting either one of those lifters in that #5 has come unclipped or is worn and rubbing, or worse, I have a cam lobe issue on that cylinder.

My thought is to pull the head and see what's happening, but I wanted to see if anyone else has had this happen, and how they addressed it.

I'm 100% sure it's coming from the internals on #5, but from the outside, I can't tell from what. Is pulling the head the right first step?

I've built race engines before and have a cobra with a 347 in it now that I just finished, but I've not dug into the internals of this 6200 before, so I want to do some investigation before. Thanks!

 

[Beartoothweb]

No one has replied, but though I'd give an update. Pulled the head and the lifter (one of them) on #5 was twisted in the guide sleeve, and was chunky and ground down. Highly likely the cam lobe will match, so out comes the engine to replace the cam, plus freshen it all up and fix my oil leak. I so wish I knew how to fix the "diesel knock" on start up that is "totally normal" according to GM.