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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: don.wooten.5 on May 04, 2014, 09:58:10 pm
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1986 chevy 305 4 barrel carb auto trans and a/c the ecm 1 fuse blew and check engine light came on truck still drives but fuse keeps popping as soon as you turn the key on any help with this would be much appreciated am worried the truck may die on me it is my only vehicle
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Welcome to the forum, Don.
More likely, that fuse is marked ECM I (for ignition power). Unplug the ECM and turn on the ignition. Does the fuse still blow? Dig out your ohmmeter and, one at a time, unplug all the solenoids under the hood that have a pink wire with black tracer connected. Carefully measure the resistance of each solenoid - each should measure over 10 ohms. If any solenoid measures under 10 ohms, it is shorted and the assembly needs to be replaced - this is the solenoid blowing the ECM I fuse. If any solenoid measures over 50 ohms it is faulty and the assembly needs to be replaced.
If all of the solenoids measure between 10 and 50 ohms, leave the ECM and solenoids unplugged to see if it continues to blow fuses when the ignition is switched on. If the fuse continues to blow with everything unplugged, start tracing the pink/black wire for insulation damage and a short to ground. Refer to the 1986 Wiring Manual (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Wiring/ST_352_86_1986_Chevrolet_GMC_Light_Truc_Wiring_Manual_CK_10_30_Only.pdf) page 12, right side, for ECM and solenoid wiring.
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i unplugged the connectors to the ecm and turned on the ignition and the fuse did not blow
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yes after plugging back in fuse blew i will have to try the mc solenoid tommorow and others tommorrow
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That was interesting. I was distracted for a moment and deleted my post - lol.
Plug the ECM back in. Does the fuse blow with ignition on? Unplug the MC solenoid and repeat. Measure the resistance of all the solenoids as earlier suggested.
Here's why - Ignition feeds through the ECM I fuse directly to the ECM and various solenoids, including the MC solenoid. If any are shorted they will blow the fuse as soon as the ECM grounds the control circuit to energize them. The wiring harness is probably okay, since the fuse didn't blow with the ECM unplugged. The least likely scenario is a shorted ECM.
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ok well this is very interesting i unplugged the mixture control solenoid and the fuse did not blow and i got my computer diagnostic (check engine light) fuctions back and then a heard a very quick clicking noise and first thought it was the clicking from the m/c soleniod but it turns out there was a bare spot on the wire that goes to the EGR solenoid that was shorting out , wrapped it with some electrical tape and so far so good no check engine light and no blown fuse seems to be running normal haven't taken it out for a drive yet but it seems to be fixed Thanks for your help, electrical problems drive me nuts
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To be on the safe side, I would cut out the bare spot and go back with butt connectors and shrink tube. Inspect the area and find would could have stripped the wire down and address that to prevent a future repeat of the problem. Electrical tape is good in a pinch but not a permanent solution.
You could even solder & shrink tube if you are comfortable with a soldering iron.
"Something" caused that wire to be bare.
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ok will do thanks again