1988 GM truck with 5.7L engine computer fuse keeps blowing

Truck wiring question

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I have a 1988 GM truck with 5.7 Liter engine. I bought it used 3 years ago and I took care of it and had no problem until today. The engine won’t start and when I looked at the fuse box, the ECM (engine control module) fuse keeps blowing. I checked for shorts and drain using my ecm wiring diagram but I cannot find anything wrong. Do you have any suggestions?

Truck wiring advice

Looking at the truck wiring diagram of this engine, your ECM supplies both power (12 volts) and ground to the whole system. To isolate the ECM, unplug it and see if the ECM fuse blows again. If it does, the problem is in the wires and loads of the ECM like injectors, solenoids, alternator, fuel pump, relays, etc.

You can then unplug them one at a time until the blowing of the fuse stops. The last component you touched is the probable culprit including its circuit. However, if the ECM fuse does not blow when disconnected shows that the ECM itself is the problem. A specific ecm wiring diagram is required for more deep analysis.

NOTES

As per truck wiring diagram, the ecm is located behind the right side of dash usually at the back of the glove box. Always disconnect the battery negative terminal when working on the ECM.

The ECM grounds the 8 injectors of this engine in order to work. Looking at your wiring diagram, power to the injectors comes to the black wire, which comes from a fuse box. However the ground comes from the black light green and black pink wires. Both of these wires come direct from the ECM.

If one of the injectors is shorted, it will blow. Also, the ECM fuse to protect itself from further damage. Finally, remember the fuse supplies from the junction box and you need the power distribution wiring diagram to check it is getting power from the ignition circuit.

What ever you do when working under the dash panel, do not touch the yellow-taped wiring harness to avoid accidental deployment of the air bag which will activate even with the battery disconnected. Remember: you do this service at your own risk.

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