Ok first off no matter what, the motor is coming out anyways. I just want some ideas and opinions so when I tear the motor down. I was making a pass the other day after switching to a smaller methanol nozzle and I was at 11psi with straight methanol on a number 5 nozzle with 100 wet shot. When I came out of it I heard a hard tapping noise and assumed it was a lifter that finally **** the bed or a bent pushrod. The motor internally is all stock. I guess it would help to know that it is a 06 5.3l. Anyways nothing changed except I had what seemed to be a little miss but wasn't throwing a code. Well I took it to the house and while driving back everything was normal, no drop in oil pressure, engine was running just as cool as well as the blower running its normal temps. So got home and started tearing it down to check whatever I could. Pulled the plugs and cylinder 7 was toast. I guess at some point it ran lean and fried the plug I reckon. All other plugs were fine. I run BR7EF's gapped at .28. Checked compression next and all cylinders had 150+psi except the same with the bad plug which was number 7, it had 125psi. I couldn't get my hands on a borescope but when I do I will pull the plug again and check it out. Next I pulled the valve covers and looked over everything. Pushrods were good as well as springs and rockers. I thought maybe it might be a lifter but by going off the pushrods before removing them they didn't have any play in them indicating a failed lifter. As of today still runs smooth. Oil pressure is still right below 40 psi at idle and over it when driving. But it still sounds like a bad lifter. I haven't really much experience when diagnosing an engine internally so any tips would be appreciated but overall I would like to gather some opinions before I do tear down and actually know what it is. I am sure I have missed something so any question just let me know. Oh AFR is 14.5-7 while driving and wot its around 11.4 give or take very little.

 

Sounds like it could be a rod bearing, but you wont know until you tear it down...

 

take a look at your filter. brass is bearings

 

There are far too many moving parts to diagnose a noise like that - valve train is a likely culprit, lifters and pushrods are the first place i would start. could justify that ugly cylinder.

 

#7 ringland chipped off, beat around until it came out the exhaust. My 05 5.3 did that, miss fired a couple times and then got better. When I pulled it to put my 6.0 in, I tore the heads off the 5.3, #7 plug tip completely gone, and ringland chipped away, but didnt scar the head? piece was gone. I drove it like that for awhile actually, thought I had bad lifter in it and said scew it, ill drive it until it dies, ran 13.2 at the track on 7 firing lol.