ECM fuse blows (Page 1/1)
edfiero AUG 21, 10:41 PM
84 Duke.
ECM fuse is blowing as soon as key goes to run position.
Disconnected cables at the ECM and it still blows. Suggestions on how to locate the problem?
Dennis LaGrua AUG 21, 11:32 PM
You obviously have a short. If its just the ECM fuse that blows it is likely a short in the ECM itself. Some other circuits may be on that fuse feed line as well. I'll check those for you tomorrow. If you need a new ECM Wayne Renninger in nearby Allentown, PA has them. Just be sure to match the ECM numbers to make sure that you have the right unit.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

cartercarbaficionado AUG 21, 11:58 PM

quote
Originally posted by edfiero:

84 Duke.
ECM fuse is blowing as soon as key goes to run position.
Disconnected cables at the ECM and it still blows. Suggestions on how to locate the problem?


if you actually disconnected the ecm wiring and it's still blowing a fuse check the wiring loom
edfiero AUG 22, 06:06 AM

quote
Originally posted by Dennis LaGrua:

You obviously have a short. If its just the ECM fuse that blows it is likely a short in the ECM itself. Some other circuits may be on that fuse feed line as well. I'll check those for you tomorrow. If you need a new ECM Wayne Renninger in nearby Allentown, PA has them. Just be sure to match the ECM numbers to make sure that you have the right unit.




Dennis, thanks for the source for ECMS but I have it disconnected and the fuse still blows, so that's not it.
Vintage-Nut AUG 22, 10:29 AM
And only as a note on this ECM thread:

I sent my computer to ECU Exchange for testing in a different vehicle as I had 'weird problems'.

From Their Service:
"Your computer had a bad power supply which created distortion on the reference and system voltages. This is due to age and not caused by anything in the vehicle."

I got it back; installed the computer and the vehicle runs great now......

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quote
edfiero:
Dennis, thanks for the source for ECMS but I have it disconnected and the fuse still blows, so that's not it.



Do you have the schematic in a manual?
Do you know to use a multimeter on resistance {Ω} to find the short?

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

[This message has been edited by Vintage-Nut (edited 08-22-2024).]

Mickey_Moose AUG 22, 02:59 PM
84 - so visually check the C500 plug to see if it or any of the wiring are melted.

This connector (on the 84 only) is between the motor and the passenger firewall near the center. It is located close to the exhaust to the point where it can easily touch the exhaust and melt.
Dennis LaGrua AUG 22, 04:18 PM
Check out leads to C1 pin 1 ppl/wht on the ECM and the pink coil lead on the ignition switch. They take power from the ignition switch. Sounds like the ECM power lead is shorted. Any disconnected power lead connection that reads to ground is a short.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 08-23-2024).]

edfiero AUG 23, 10:28 AM
Just to close the loop on this...... I think I have found the problem.

I am using a 3rd party ECU. And although I removed the two main connectors from the ECU, I neglected to remove one standalone wire which connects to a wideband O2 Sensor.

It appears that the wire to the O2 sensor was shorting, as the insulation was rubbed/burned off. After adding some new insulation to this wire, the fuse stopped popping.