2013 PPV/Newbie- hello

[Will L]

On a couple other forums for different rigs, but not tech/media savy.
Got a 2013 tahoe ppv at auction.

Gonna do reading but bad at finding stuff, links to help me find things are appreciated.

I want to do AFM delete in future if I decide to keep this long term- don’t wanna do it then sell If the wife doesn’t like the truck.

Having a intermediate cylinder misfire from calm to major. But it is not one of the AFM cylinders.

Changed spark plugs, coil, that bank of injectors. Misfire/ low relative compression stayed on that cylinder. I have to check notes to see which exact cylinder.

I was a mechanic on older cars (carburetor no electronics, and diesel) but cant diy much on this. Currently rebuilding my diesel and being old & busted up means that project has me tied up. So at a shop I can trust the owner isn’t a thief but not sure how good his mechanics are. The owner was a good mechanic in gm dealership for years until around 2005ish when he opened his own shop.

Any links about this on non AFM cylinders is greatly appreciated!

 

[Miami-Dade]

Welcome from Miami&Queens NY!

@Will L Moved you here for your issues. Will eventually move you to the PPV section.

 

[rdezs]

"Low relative compression"..... How much compression are we talking about? And does the compression test improve after inserting some oil in the cylinder?

I would do a leak down test as well, prior to pulling the head. Pressure check the cooling system definitely.

Diagnostically narrowing down the source of the low compression is pretty much similar to the old small block Chevrolet's used to work on. Basically rings, piston, head gasket, valves or a possible crack in a component. A collapsed lifter on the intake side could prevent the intake of air, but you would be hearing a definite lifter tick

The one major difference in addressing this on an LS engine is that you can't remove the lifters without pulling the heads. So whenever the heads are off, you really want to replace the lifters and the lifter trays. Also, the cylinder head bolts are one time use torque to yield. Replacements are not expensive, but I always spend the $160 or so and get ARP head bolts that you can reuse.

 

[Will L]

Sorry for the long time delay getting back here.
I’m not personally working on this yet- between work and an injury, I am trying to get this done at a mechanic shop.

This is cylinder 3 btw.

First mechanic is the one who said it was a relative compression comparison he did with a scanner reading something. He put in the new plugs and swap coil locations and misfire stayed at cylinder 3. He said he did regular compression test and everything seemed normal and leak down test showed all ok.
He traced harness a bit and didn’t find anything, didn’t touch it for a while and basically said he didn’t know what else to do other than complete tear down-so I took it to a different shop where I know the owner better (i was a Mac tools guy for them for a few years until 08-2010 crash killed business).
This guy says intermittent or constant electric issue to the spark or injector can cause what he saw on the comparative “compression” loss because it’s really measuring voltage changes.

Tech at his shop did actual compression test and leak down also- both ok. He thought injector so with about 75,000 miles on it plus idle time for a/c since cop car here in desert heat. (Boulder city next to Las Vegas). So we are treating it like same miles idle time. He suggested injectors but it didn’t seem right to me. So I only paid for that bank of 4 injectors and if I keep truck I will do the other 4. That didn’t fix it.

They pulled that valve cover and the valves are working as it should. He verified it’s cylinder 3 so not an AFM issue. They put it back together and are thinking something in the electrical system, but neither shop suspects anything with ecm.

It was a cop car and the city mechanics stripped the gear out of it before auction.

In talking to the 2 shop owners and the tech that worked on it- they think maybe damage done while removing the police equipment.
Each shop did a few other repairs needed like blower motor replaced (squeaking). Got rear door locks & interior handles working again (disabled for suspects in back seat), oil change, etc.
The second shop also suggested finding a different shop for chasing the electrical ghost they blame on the OCCASIONAL dead cylinder.

But other than just manually tracing the wiring harnesses- I am not sure where else to go.

Any input would be greatly appreciated.

Also I have a blower motor for a non ppv tahoe if anyone local wants to pick it up. I got it new from a parts house that went out of business and it was wrong one for my tahoe. I can post part number if anyone is interested- just not near truck now.