Car wiring question:
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 wont 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?
A quick way to test this is to check the VREF voltage of one of of your sensor. It should be 5 volts. If lower, it is shorted to ground. If higher, it is shorted to power.
Take a look at this Ignition circuit diagram above. Looking at the steering column wires for the ignition switch wires, you will see a pink wire coming out and that goes to your 10 amp fuse then finally at the ignition control module. When you turn the key on and using a test light, check for 12 v supply at B Pink wire. Same at D C3 going out to D5 until you reach B C3 at Ignition coil wiring harness.
By keeping an eye on the brightness of the test light, you can see where the light goes dim which shows poor circuit connection. You can also use a voltage meter and see if the voltage reading is dropping. A voltage drop indicates poor connection or even a bad ignition switch.
Thanks for your help! I put my test light at the pink wire at Ignition control module and it was dim. Changing the ignition switch fixed the problem.