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Discussion Starter · #1 ·
Long story short over the last year and a half I have had some issues with my ECM Connections mainly the two larger connectors right at the ECM.

2008 LMM

Started off as Cyl 5 Misfire code early last year all balance rates read 0 and truck ran terribly. Dropped it off at multiple shops and a reputable one here in NC final census was bad injectors. Ordered OEM injectors installed them and Cyl 5 misfire came back about 2hrs later. Grabbed close to the ECM connectors wiggled the wires and problem went away.

Now I get P0301 Cyl 1 Misfire code no symptoms like the Cyl 5 code had and truck runs normal. Usually clear it out and keep riding.

Took a 3hr trip yesterday and I started getting a P2152 Group C Injector code about 2hrs into it, pulled over removed both connectors hooked them back up and the code went away. No more codes since.

Figured since I have a couple days off I'll actually check each wire/pin since it seems as maybe a connector may be loose or slipping out of place after a while, or the male connector on the ECM is worn down. Thinking maybe Cyl 5 Injector is the one causing issues but Cyl 1 is the one I have consistently gotten, does anyone know if these share a common ground or something within the ECM harness?

Also anybody have a smart way to verify good pin contact since Im not sure ill be able to removed the top of the connector to probe the pins and keep it connected to the ECM...
 

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See attached showing how the fuel injectors are paired up. Wiring diagrams are available at Body Builder Manuals - GM Upfitter

1 pairs with 4 -
6 pairs with 7 -
2 pairs with 5 -
3 pairs with 8

The problem could be in the wiring or connectors, or it could be a bad ECM, or something else. Since it doesn't always misfire in the same way, it will be harder to determine exactly what is happening. You might try some DeOxit spray on the injector connectors and on the ECM pins, Just takes very little. If you had a scope, that would make the testing easier because you could see the engine firing while it is running and compare one cylinder to another.
 

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Discussion Starter · #3 ·
Only one that seems to be persistent is Cyl 1 all the others showed up once I started moving the harness. Looks like I’ll check 1 wiring first. Luckily I have a spare ECM from a while ago just waiting for my tuner to send the new file
 

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Discussion Starter · #4 ·
So after a lot of depinning and cleaning it appeared my problem was the plug tightening itself too much when it was closed. Noticed if I loosened the lever it would go a way.

Guess at some point I didn’t reassemble it in the released position. Still going to swap ECMs as I don’t think it should matter if the plug is too tight but we shall see.
 
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