89 electrical

[Mathies]

hello

could someone maybe help me

my ecm burns internally on pin C16 thats where the 12V come from the fuse link.
i disconnected al the plugs from my pickup but it stil burns out. if i put 12V on the ecm and ground it on the batt it doesnt happen.
so im guessing something is shorted out from the wires. i checked al the whires but cant seem to see a short in any of the wires. is there any place i schould be looking extra some spots that are know to short out.

im really scratching my head and almostt at the point of just selling the truck so any help would be greatly appreciated.

 

[Mathies]

i also disconnected al the fuses, relays nothing seems to work/help

 

[GoToGuy]

Make, model, year, engine, trans ? Are these all the same problem or are you having continuous different problems?

 

[Mathies]

Its a gmc sierra k1500 from 1989 5.0 v8 with a 700r4 transmission. First had no spark changed spark plugs, icm, rotor, cap, coil and pickup coil had spark.
No fuel pump prime. Changed fuel filter an fuel pump (it wasnt bad but changed bcs it would probably go bad in the nezr future). Stil no prime. Replaced fuel pump relay still no prime. If i jump relays pump works fine.

With the help of some helpfull people here i could diagnose ecm was blown internally. Had it repared by a ecu expert. But then when wanting to try again i put an inline fuse on the cable that runs to c16 on ecm from 10A and this one still burns out with al the connectors disconected from the truck. The fuse doesnt blow when i disconnect ecm and run inline fuse from +batt to c16 and d1 ground ecm to ground on -batt.

 

[Schurkey]

my ecm burns internally on pin C16 thats where the 12V come from the fuse link.
i disconnected al the plugs from my pickup but it stil burns out. if i put 12V on the ecm and ground it on the batt it doesnt happen.
so im guessing something is shorted out from the wires.

i could diagnose ecm was blown internally. Had it repared by a ecu expert.

The ECM is "burning" internally. I'd suggest a potential internal problem with the ECM that the "expert" missed.

But then when wanting to try again i put an inline fuse on the cable that runs to c16 on ecm from 10A and this one still burns out with al the connectors disconected from the truck.

How is C16 protected normally? In '88, it's a fusible link, but the service manual doesn't show what gauge it is.

There's hundreds of "connectors" on your truck, from the front bumper to the rear bumper. WHICH ONES are you disconnecting?

The fuse doesnt blow when i disconnect ecm and run inline fuse from +batt to c16 and d1 ground ecm to ground on -batt.

So C16 doesn't draw excess current unless the rest of the ECM connectors are hooked-up?

What does the schematic show that C16 powers-up? In '88, according to the '88 Fuel and Emissions manual, C16 on V6 and gasoline V8 engines has something to do with the fuel pump relay circuit. Look for melted/shorted wires on the relay trigger circuit--Cavity A1 at the ECM, circuit 465, green/white wire, cavity "D" on the 5-wire relay connector.

 

[Mathies]

c16 is protected by a fusible link and it reads 0.5 SQ. MM Fusible link it the grey one in the picture it also says 20 but idk what that means. i also find it kind of strange the fusible link still works.

so So C16 doesn't draw excess current unless the rest of the ECM connectors are hooked-up?

yes if none of the ecm connectors are hooked up c16 doesnt draw excess current.

c16 powers up the ecm, fuel pump relay(wich is disconnected), hot fuel module
the wiring diagrams says the hot fuel module schould be behind RH side of I/P above blower motor. the only thing there are 3 relays wich are also disconnected.

Soo i disconected the instrumental panel cluster, the light switches, the 3 relays above the blower motor, the ac, alll of the fuses, the o2 sensor, icm both plugs, coil both plugs, map sensor, egr module, TPS sensor, coolant sensor, fuel pump, esc, all of the transmission plugs even the front diff, the connector that connects the wiring harness from right to left under the dash, connectors i dont even know what they do, the radio, the idle air control, the cigarette lighter, the rear lights, both injectors

thanks i will double check those wires

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[Mathies]

i double checked those wires they are all good and no short to ground. i even unplugged al the other fusible links on the junction block so no other component other than my ecu and starter could recieve power. the inline fuse i put in myself still burns when i try to aplly 12V to my grounded ecm. i even unplugged my starter 12V and signal wire from the starter.
could it maybe be its the ecm that is failing?
also the black/red wire going from the batt to junction block is completely fine even where it runs between engine and exhaust
im really really losing my mind on this problem and the problem is i cant bring it to a mechanic first there are 0 GMC mechanics in my country and the truck doesnt run so i cant deliver it to one. i need to fix this truck asap bcs im moving and if it doesnt run i will need to sell it.
hopefully one of u can help me i know its a really long shot.

 

[Mathies]

is there also a way to check the place where the cables go trough the firewall to the ecm on the passenger side?

 

[Schurkey]

Plug things back in one at a time until the fuse pops. That'll narrow-down where the problem is.

 

[Mathies]

Thats the problem the fuse always pops. This is how i wired the last time and the fuse stil popped.
JB is junction block and the wire going to c16 is the only one screwed to the junction block and ofcourse the batt cable

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