Cylinder 7 misfire caused by flaking lifter chrome

[Uscgevo]

The engine is a 6.2 in a Yukon Denali without AFM or cylinder decactivation I have done lots of research and have looked into the typical causes. Here is a list of the things checked and replaced:
-Compression checked good
-No play in rocker arms at multiple crank positions
-Swapped in multiple coil packs, checked coil pack harness with a meter
-New injector, plugs, wires, camshaft sensor, crank sensor
-Swapped the new injector to another cylinder to rule out a bad new part.
-HP tuner software killed the injector and it got worse

I am really at a loss with this one. Car seems to run fine. No power loss I can tell. Gas mileage seems to be normal, 13-17mpg depending on driving. Not sure what else it could be and I don’t suspect the lifters as I have no play in the rockers. Please help and let me know if you have any ideas or other checks I could. Wish my first post was under happier circumstances. Thank you in advance for the help.

 

[swathdiver]

Howdy Chris, so this motor is the L9H? Where do you live? Maybe someone has a Tech2 that can take a look inside your system and see what's going on?

We've seen a few folks lately with 6.2s with busted valve springs.

 

[Uscgevo]

Howdy Chris, so this motor is the L9H? Where do you live? Maybe someone has a Tech2 that can take a look inside your system and see what's going on?

We've seen a few folks lately with 6.2s with busted valve springs.

I think it is a L92, but could be wrong. I have checked the springs a couple times, but then again it is possible to have missed. I am located in Miami

 

[kbuskill]

Dumb question but have you actually checked to see if the plug is firing with a tester or even with a spare plug that is held to ground?

 

[swathdiver]

I'm over 2 hours north of you. It is my understanding that the L92 had AFM hardware but it was not activated via the tune. There's plenty of guys on here from South Florida, let's see if one has a Tech2 and chimes in.

 

[gpracer1]

CASE relearn?

 

[Uscgevo]

Dumb question but have you actually checked to see if the plug is firing with a tester or even with a spare plug that is held to ground?

Checked via switching in multiple coil packs and spark plugs and then finally replacing the spark plug and wires.

 

[Uscgevo]

CASE relearn?

Tried prior to replacing the cam sensor and it did not go away. Disconnected the battery last night to see if it changes anything or initiates a relearn. I don’t have the software available to me anymore.

 

[Uscgevo]

I'm over 2 hours north of you. It is my understanding that the L92 had AFM hardware but it was not activated via the tune. There's plenty of guys on here from South Florida, let's see if one has a Tech2 and chimes in.

This is true which why a lot of Denali guys still manage to get collapsed lifters, but I have zero play in my rocker arms so I don’t suspect that could be the issue.

I am about to pull my valve springs to inspect them. Hoping I pull them and one is actually broken and I just can’t see it

 

[kbuskill]

Checked via switching in multiple coil packs and spark plugs and then finally replacing the spark plug and wires.

Something like this would verify that you are indeed getting spark.

Or

Swapping parts would be of no benefit if the wiring providing the power or signal to the coil pack were the problem.... or something further up stream.

Hell even a screw driver stuck in the end of the plug wire and held close to ground will work.

 

[Uscgevo]

Something like this would verify that you are indeed getting spark.
View attachment 192378
Or
View attachment 192379

Swapping parts would be of no benefit if the wiring providing the power or signal to the coil pack were the problem.... or something further up stream.

Hell even a screw driver stuck in the end of the plug wire and held close to ground will work.

I tested the wires with a multimeter and just for fun tested it by grounding the plug after you mentioned it. She fires.

 

[kbuskill]

Then it is either fuel or compression related. You swapped injectors so that likely rules out fuel... unless again something were wrong further up stream in the harness. But you said killing the injector via software made it worse so that's out.

And you said you checked compression and all was good. So that likely rules out lifters and burnt valves.

I would have guessed a cracked plug but you said you replaced them.

What octane fuel are you running?

 

[swathdiver]

Plugs aren't hard to crack, swap cylinders.

 

[gpracer1]

We are all assuming that it really is misfiring. Can you feel it misfire or is it just the computer telling you it is misfiring?

 

[Uscgevo]

Then it is either fuel or compression related. You swapped injectors so that likely rules out fuel... unless again something were wrong further up stream in the harness. But you said killing the injector via software made it worse so that's out.

And you said you checked compression and all was good. So that likely rules out lifters and burnt valves.

I would have guessed a cracked plug but you said you replaced them.

What octane fuel are you running?[/
I only 93 in it, and from shell and chevron because it seemed to make a noticeable difference.

 

[Uscgevo]

We are all assuming that it really is misfiring. Can you feel it misfire or is it just the computer telling you it is misfiring?

I can’t feel it but the software counts them up at idle and sub 2k rpms. Over 2k it doesn’t show any misfires occurring. WOT it still pulls like crazy and runs perfect according to the software.

 

[Uscgevo]

Plugs aren't hard to crack, swap cylinders.

Did that even after putting new plugs in. This really has me stumped. Usually everything I have checked would have either fixed it or at least told me what broke. Honestly the only reason I care is it my wife’s car and want the auto start to work this summer so she can cool the car down for the kiddo. Florida summers suck and that feature was awesome to have.

 

[swathdiver]

Florida summers suck and that feature was awesome to have.

Where in Florida? There's a number of Floridians here on the forum and some have advanced scan tools that can help.

 

[Uscgevo]

Where in Florida? There's a number of Floridians here on the forum and some have advanced scan tools that can help.

I am in Miami

 

[swathdiver]

There's a bunch of guys on here from Miami and surrounding parts. Let's hope they chime and get over to your place to help out.