Short in ECM-B circuit, 1991 V2500 Suburban 5.7L

[GaBnn3]

I have a short in the above circuit that blew several Ignition Control Modules as well as the fuse. This circuit runs right under and behind the distributor. It seemed a little over my head, so I took it to a garage. They replaced a section of the circuit with worn insulation and told me it was fixed. It died on the way home and went back to them with the fuse blown again. They tightened down the wire harness and said it should be okay now. Not very reassuring. Much of the original wire mold is gone now. It made it home but repeatedly skipped. The Ign Cont Module in there now is an OEM style from Advance Auto Parts that cost twice as much as the others. I think the module did not blow because it is higher quality than the others. But for reliability I believe that the entire circuit needs to be replaced under the hood. It ran great before the problem began and did not skip. That circuit goes from the fuse block to a splice (S140) with four outputs: one to the fuel pump relay, one to the oil pressure switch and two through the firewall to ECM connectors. Has anyone replaced this circuit? Is it a good idea? What kind of splice connector did GM use? Any help would be greatly appreciated. I don't think it's suitable for a long trip as it is. Thanks.

 

[BoondocK5]

Does your local picknpull have any trucks with the same harness? Which you could harvest the harness from. That is my preferred route to take in these instances.

 

[ZooMad75]

I had a similar issue with that fuse popping after my ls swap. We used as much factory wiring as we could so the ecm-b fuse powered my ls ecm.

Mine would pop the fuse after 15-20 minutes of runtime. The odd thing was that the fuses when blown didn’t looked popped (like having the little black charred marks) as much as they melted and opened.

On a suggestion I got and used a tool called a fuse buddy. This device plugs in place of the fuse that’s popping and allows you to watch how many amps the circuit is pulling and see what’s going on.

In my case the circuit had a 20 amp fuse on it stock. When I watched with the fuse buddy it was consistently pulling 19 amps all the time. Not shorted but fuses don’t like being maxed out and it was the reason mine were melting.

I bumped the fuse up to a 25
Amp unit and it never popped since.

Keep this in mind DON’T just blindly throw in a higher rated fuse without knowing what the circuit is actually doing. If the fuse is popping as soon as you power up the circuit it’s got a dead short. If the fuse takes time to pop it might be pulling at the limit. That’s where the fuse buddy was perfect to figure it out.

 

[rampage]

I had a similar issue with that fuse popping after my ls swap. We used as much factory wiring as we could so the ecm-b fuse powered my ls ecm.

Mine would pop the fuse after 15-20 minutes of runtime. The odd thing was that the fuses when blown didn’t looked popped (like having the little black charred marks) as much as they melted and opened.

On a suggestion I got and used a tool called a fuse buddy. This device plugs in place of the fuse that’s popping and allows you to watch how many amps the circuit is pulling and see what’s going on.

In my case the circuit had a 20 amp fuse on it stock. When I watched with the fuse buddy it was consistently pulling 19 amps all the time. Not shorted but fuses don’t like being maxed out and it was the reason mine were melting.

I bumped the fuse up to a 25
Amp unit and it never popped since.

Keep this in mind DON’T just blindly throw in a higher rated fuse without knowing what the circuit is actually doing. If the fuse is popping as soon as you power up the circuit it’s got a dead short. If the fuse takes time to pop it might be pulling at the limit. That’s where the fuse buddy was perfect to figure it out.

You would also need to make sure the wire is the correct gauge in order to handle the increased amperage or bad things could happen.

 

[Wes Harden]

The s140 splice is a metal butt connector, with drink tube over it in the loom protected by a cover and tape.
If your distributor is original, the internal wiring is suspect. Esp the pick up coil wiring.
Also inspect the wiring to injectors where it passes into the air cleaner assembly.

 

[GaBnn3]

My truck is 4WD with the 4L80 tranny. However, I located a good wiring harness from a 1994 Chev Silverado, 5.7L, 4L60, 2wd. Can anyone tell me if this is correct for my truck. Thanks.

 

[Wes Harden]

No the 4l60 and 4l80 are different monsters. The 4l60 uses a 4 wire plug.
4l80 is 12? Wires plus 2 other connectors for the speed sensors.
Not sure on the neutral safety switch

 

[Wes Harden]

It doesn't have to be loom. The actuators and sensors on that circuit could be shorted to ground.

 

[swettysblazer]

Check the oil pressure sensor. My wiring was chafed right there on my 1991 and it drove me crazy. The wire rubbed through when I did a cab swap and arced on the firewall.

 

[GaBnn3]

Thank you all for the helpful tips. I will be working on it.