M122 blown 5.3 in my 99 silveraydo

[Vbb199]

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.

 

[Vbb199]

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

 

[Vbb199]

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 ?

 

[Vbb199]

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

 

[Vbb199]

i did a little learning and as it turns out IGN1 grabs its ground off of a bunch of sensors in series.

F6 in the RED underhood fuse block.

C-3 — 1999 Chevrolet C 1500 Truck 2WD V6-4.3L VIN W Service Manual | Operation CHARM

Detailed repair manual for the 1999 Chevrolet C 1500 Truck 2WD V6-4.3L VIN W.

charm.li

so today i pulled the whole chassis harness off the truck to look into this broken ground situation.
I needed to pull it anyways, because i wanted to run a dedicated 10g wire for the hellcat pump.

i pulled it out, and upon looking, i learned that IGN1 grounds itself immediately to the brake booster fluid level switch. and then runs in series thru sensors.

Engine Oil Level SW, Engine Coolant Level SW, Underhood Lamp — 1999 Chevrolet C 1500 Truck 2WD V6-4.3L VIN W Service Manual | Operation CHARM

Detailed repair manual for the 1999 Chevrolet C 1500 Truck 2WD V6-4.3L VIN W.

charm.li

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i stripped the harness down to bare wires. i didnt chase where the ground breaks at yet, but im assuming its probably somewhere in the series.


i also went ahead and took the gas tank out, so i can drop that big pump in.

 

[Vbb199]

Something is definitely off with that whole harness anyways, which i will get to the bottom of.

The ABS module had a heavily corroded ground (it uses 10g power)

The fuel pump + pin was melted around it

The trailer plug harness had badly burned wires in one spot

Obviously this part of the harness has been struggling for a bit.


Fwiw the frame grounds to battery. So the frame being ungrounded wasnt the issue.

 

[Vbb199]

See, I thought i was done with wiring but I guess not.

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Regardless the chassis harness is redone, with accommodations for the 525 with appropriate gauge wire, with a 40a relay.

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Factory pump wires are gone, its now powered by the 10-12g wires it comes with from the 20a maxi fuse slot I will use at the underhood fuse center

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Just need to find a 99-02 maxi fuse single plug.

Grounds everywhere in the series are redundant and chained, and there will be 4 points of contact along the frame for grounding.

No more electrical tape from the PO either. All soldered and heat shrunk connections.

 

[DoubleDingo]

Very nice. Hopefully that killed all the gremlins

 

[Vbb199]

I hope so! And ill feel good re-connecting the trailer plug that was previously melted under the hood.

I wanna tow with it.

Even if this doesnt solve it, my next place to visit will be the grounding hub on these trucks

Im so invested at this point.

Splice Pack 203 (SP203) — 1999 Chevrolet C 1500 Truck 2WD V6-4.3L VIN W Service Manual | Operation CHARM

Detailed repair manual for the 1999 Chevrolet C 1500 Truck 2WD V6-4.3L VIN W.

charm.li

Splice pack 203.

Located around the column area.

 

[Vbb199]

The biggest thing that I think will put it to rest is, the IGN1 ground ran to the brake booster plug, as shown in that diagram I shared.

The other pin on the the BB plug rung out to the ABS module bulkhead


The ABS module uses big 10g power and ground, and the ABS' ground wire wouldn't show continuity to battery (-) when it was on the the frame, and the IGN1 didnt show battery (-) on its relay either,



Believe me, I dipped the eyelets in acid, scrubbed them, and will scrub the frame clean too.

 

[Vbb199]

It kinda makes me wonder too because the PO had hacked up the steering column, bypassed VATS thru hard wiring.
There was power and perhaps ground being grabbed off an O2 sensor circuit i found on the old 4.3 harness. The old steering column rocker switch was zip tied under the dash, and there was a push button where the key and cylinder used to go.

You had to turn the rocker, then press the button to crank it

I just assumed replacing the column would fix it all lol

I asked him why they did the column like they did and it was because it wouldnt start
Could've been ign1 grounding all along, I dunno

 

[Vbb199]

Bleh. pos truck hahahahahaha.

I put the chassis harness on last night and scrubbed and scuffed the frame at all the ground points.



Ign1 grounds to battery (-) now and the underhood trouble light comes on as it should.

the headlights now cycle on with a key, high and low beam works, turn signals work. interior lights work. HVAC controls work!!!!


Thats all good. If I pull the ign1 relay I dont hear clicking and shorting everywhere inside either.

SES displays on the dash when I turn the key, but i dont get the message center or any of that other stuff


Just as a little test I plugged in the bistable relay, 2step button, and tow haul LED.

The bistable relay began smoking from a 16g input wire and didnt recognize any tow haul input.
(It would click the relay on and off before)


So i got a feeling ive got another broken ground or issue somewhere else in the system
Theres a data link connector and a 8 pin ground connector that im going to next.

 

[Vbb199]

Yesterday evening I printed out all major ground locations on the truck from charm.li

Today i went one by one checking for issues, even tore the whole dash pad off.

The first biggest red flag of all was the fact I grounded the battery to radiator support which I believe is isolated from the chassis except thru body bolts.

The engine is grounded to the battery, the engine is grounded to the cab, and the cab has some big girthy cable thingies that run from frame to cab at each rocker of the truck, buttttttt

The frame still had no direct line to the battery. So theres that.

I scuffed the frame to bare metal and attached it.



Second not so serious issue I found was my hood to cab ground strap was nearly severed, but again I dont think that matters ? Maybe im wrong. Regardless I crimped new ends on, soldered everything solid, and cleaned and re attached those grounding points.




Moving into the cab, I had to take apart the whole dash pad and all the **** for the cluster, vents, switches and knobs, so i could check my cab grounds.

Its like G203 and G200 or something at each A pillar, and all of the interior stuff behind the dash terminates at G203 in a splice pack, then terminates to the cab. All of that rung out to battery (-)

I have no idea if it did before i fixed those aforementioned grounds, and I guess i dont care, lol

I checked grounds everywhere and anywhere I saw them inside the truck against battery (-) and all showed continuity


Then I began checking the instrument cluster plug. Theres pin A8, circuit 451 called "ECM ground"
And it didnt ring back to battery negative

So maybe there's a good clue. Because if you dear reader remembers, I could plug my scanner into the OBD port and then the instrument cluster would come alive.

Which btw that ground at the OBD2 (data link connector) rang to battery (-)

So i THINK im getting somewhere, and am currently looking over circuit 451 in schematics and learning where it terminates.

 

[Vbb199]

yuppp yup

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[Vbb199]

totally random, i know, but i share the same first name as his son-

but @Ricko1966 ... im surprised you havent ever commented!