Gen4 5.3 Misfire
 

2010 Tahoe 5.3
bought it with lifter tick, stuck lifter on 3.
Replaced Cam and Lifters with stock replacements along with all associated gaskets etc and it ran good
Out of the blue it started running like garbage, hooked up scanner and watched misfires on #3 with an occasional miss on 5, then 1 and 7 even less frequently.
Went digging, replaced intake gaskets and injector O-rings, swapped plugs, wires, coils, injectors, coil pack harness and MAF. Nothing has changed the misfire.
It idles rough, drives fine under normal load, after 3500rpm itll bog down, wont shift and ping like all hell from the driver side and #3 lights up with misfires. sometimes the traction and stabilitract messages will appear and power will pull until the truck is restarted again.

Wiring harness damage to ecm maybe? Odd that it's only that bank.. 1, 3, 5, 7. Makes me think its it's related to something injector wiring or coil related on the side, like before the coil harness itself.

We thought that too. Checked the pins into the engine side of the coil harness and they were all seated correctly. Need to find a wiring diagram for it tho. It's primarily #3 which is where the original stuck lifter was which is odd. I traced the #3 injector wire to the ECM and it was good.

How are your grounds?

The ones I've found so far were all good, cleaned and reattached

Do a compression test yet?

thats next up, hopefully tomorrow

What do the plugs look like?

I'd still go over grounds again. IIRC there should be one from the firewall to drivers side head, then from divers side head to passenger side head. If this isn't there, I'd add it

plugs were all old, with the exception of #3 which i assume was changed by the PO trying to diagnose the stuck lifter. i replaced em all, all look the same currently.

grounds i recall the big fat braided wire from the drivers head to the firewall, and i believe a separate from from pass side head to the firewall? ill check again tmrw.

Bank 1 compression


1 - 160
3 - 147
5 - 147
7 - 150

Those numbers seem good. I think that's only 8 or 9% variation.

A thread I just read on a chevy truck forum had a similar issue which turned out to be the pin in the harness to the ecm was bent and/or pushed back just enough to not make good contact. Once pin was corrected, truck ran great. Worth taking a look.

I traced both the #3 injector and coil wires back to the ECM, both were unbroken and seemed good. Really impossible to see into the pin holes on the EMC side, they so small lol

Clogged driver side cat was the cause. Hollowed all 3 out and she runs great again.