I have reached the end of my diagnostic skill and need some help. Project has been a long time developing and still a long way to go. Motor was built a couple years ago, fired and run in. Recently completed enough fabrication and paint work to start reassembling everything. Reinstalled motor, fired up.
I did not have an infrared temp gun when I first ran the motor in, so I can only assume this problem existed from the original build.

8.1L from 2003 Avalanche
Stock components except
Raylar cam - Intake 224/.509 Exhaust 237/ .545
Raylar springs & retainers
Roller rockers

#8 cylinder 150F
#6 cylinder 195F
#4 cylinder 250F
#2 cylinder 250F
#7 cylinder 260F
#5 cylinder 300F
#3 cylinder 285F
#1 cylinder 250F

Compression Test
#8 cylinder 175psi
#6 cylinder 175psi
#4 cylinder 180psi
#2 cylinder 180psi
#7 cylinder 180psi
#5 cylinder 180psi
#3 cylinder 180psi
#1 cylinder 180psi

Swapped #6 coil with #8, no change in exhaust temps
Swapped plugs from bank 1 to bank2, no change in exhaust temps
Swapped plug wires from bank 1 to bank2, no change in exhaust temps

Harness was from a 2004 avalanche, and I have modified /cleaned it up. So, I checked it from the PCM harness all the way to the injector plugs. All connections ohm out okay and match up correctly pin to pin.

Injectors were all new on originally startup. They all currently ohm the same at 12.8.

log file and tune file attached

Something is going on with #8 and #6 based on the compression test, but that's still pretty close to same number. When the motor cools down I can pull the valve cover.

Could this just be the result of a slightly incorrect valve lash? Push rods were custom length due to rocker arm swap.

 

"Injectors were all new on originally startup. "
I'm betting on a stuck/poorly flowing inj. Having fuel sitting in them for 2+ yrs, is not good.
As for 5psi difference in compression reading...Not a problem.

 

As the man said, injectors are your next step. Swap #8 with an easy-to-reach one and retest.

 

Checked with Noid light yesterday (OK) and a redneck stethoscope. There is definitely something wrong with #8 injector.

 

frequently, when I clean/flow injs....Especially with junkyard engines.

The fuel is so poor, that some small engine mfgrs are saying fuel storage should be limited to 30-45 days.
In fact, some are making $$, by selling small qtys of pure fuel... no ethanol in it.

 

Swapped in one of the old injectors after flowing some cleaner through it and there is a definite improvement. Exhaust temps came up on 6 & 8, and the whole bank 2. 6 & 8 are still a bit lower than all the others. by 30 F. STFT's are consistent from Bank1 to Bank2.

I may try readjusting the valve lash on 6 & 8. Suggestions?

 

I had the similar thing happen on an old AMC 360. I could tell they were running cooler because the paint didnt burn off the primaries on those cylinders. Had to relash the valves and everything was normal.