M122 blown 5.3 in my 99 silveraydo

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Service engine soon turns on without the key switched and the fuel pump also turns on without the key switched.

So yea. Trucks got issues without me tampering.

 

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After spending over 8 hours with this POS I think I found my issue.

Starter wasnt clicking because im dumb. The relay was missing its ground and trigger pin. Lol
The 2004 handles it thru ground and the 1999 i think does it thru the bcm and other ****... I gotta get a direct line from the column.

I confirmed engine to motor ground is fine and motor to body is there.

But here's what I think is wrong: please if someone here knows ****, tell me. Im just going wire by wire trying to find the issue.

At the tail end of the day i learned that big IGN1 relay that turns on when you switch the key to "on' and "crank" has something strange with its ground.


Pin 87 of IGN1 is battery +
I saw continuity here

Pin 30 of IGN1 dumps to a large section of pins on the fuse block, including starter relay power. Pin 30 was powering holley injectors, motor coils, flex fuel, trans solenoids, bbv solenoids, etc etc. All on their own fuses in C2.

Pin 85 of IGN1 confirmed to switch on and off with 12v when I turned the key to "on" or "crank". (Key off killed pin 85)

Pin 86, which is SUPPOSED to be ground WOULD not ground to battery, or to other grounds on the fuse block


Time out lol

So im theorizing IGN1 is/was grounding itself thru EVERYTHING when I shut the key off. It'd make sense why the fuel pump cycles when i turn the key off.

When the cluster dances... why the holley didnt die. Why the tow haul abd 2 step LEDs stayed lit no matter what

Just a thought


Anyone have input if you follow me? IGN1 is a big circuit lol

 

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The big red flag for me is when I connect the battery, nothing happens.

Its only UNTIL I turn the key on, then back off does it start acting stupid.


That and when i connect the OBD2 interface , the instrument cluster comes alive lol

The MPVI is internally completing the path from the PCM power to ground so it stops hunting ground thru accessories and so forth.

Pcm is powered off IGN1
ign1 powers the OBD2 port somehow. Maybe thru PCM too

Thats the "smoking gun"

It takes that shortest path to ground, but stuff still acts stupid other places.


Thoughts ?

 

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I also want to add that after keying on and off, if I pull out the IGN1 relay, the relays in the truck will click on and off every couple of seconds.



So what im finding is;

Those relays clicking are apart of the retained accessory power circuit, inside the cab.



Because when I pull the IGN1 relay, that ungrounded power stays trapped in the relays, BCM, etc

It cycles thru continously, because IGN1 grounds itself thru other stuff, its keeping the PCM alive.. (hince the check engine with key off), so the pcm continues to power the 4L80e solenoids, holley stuff and so forth.

The bcm interprets that as me turning the key on and off, so its cycling those relays