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Old 12-21-2006, 05:53 PM   #1 (permalink)
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Blown ECM Fuse - WTF's Going On??

I'm in the final stretch with a 350 swap in my 1991 C1500 pick-up. I had good spark and gas, the engine was running rough but I was almost there. Then, all of a sudden, no more injection from the TBI..........

After looking everywhere, I found that the ECM fuse was blown. I changed it out and tried again, only for it to blow again, this time immediately. Getting out my trusty voltmeter, I searched around for the short and found that the electrinic spark module, ECS, is going directly to ground. However, about this time, it got too dark to see what I was doing, so I packed it in for the night.

The ESC has four wires:
- PNK/BLK = ignition switch power
- YLW/RED = ECM in
- BRN = ground
- DK BLU = knock sensor


Can anyone give me insight as to what voltages I should find on the YLW/RED and DK BLU wires??

Any other tips or tricks??


TIA
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Last edited by billj; 12-21-2006 at 05:55 PM.
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Old 12-21-2006, 08:22 PM   #2 (permalink)
j5
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A shot in the dark: I was blowing fuses suddenly. An 02 wire dropped onto the exhaust pipe. The preheat would keep blowing a fuse and throwing MAF and cam sensor codes after the blow. This is a WAG however.
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Old 12-22-2006, 08:27 AM   #3 (permalink)
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wiring diagrams

Here is the pinouts for the 7747 ecm.
There may be some wiring color dfferences but just go by the "key on" voltage checks listed on the outside margins.

The ESC provides a 9V signal to the ECM.

You can unplug the ESC and the engine will still run. But the timing will be retarded.
If you want a way to eliminate the ESC you can go the FI forum listed in my sig and read the wiring FAQ.

IMHO I doubt the ESC is your problem.
Sounds like a pinched wire somewhere.

Your better off with an ohm meter and the diagrams and reading each wire from the ECM connectors to it's sensor, looking for shorts.
Just unplug the ECM and use a small piece of safety wire or a paper clip in the connector if your leads won't reach.
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Old 12-22-2006, 12:07 PM   #4 (permalink)
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Thnaks for all the info, now I've got a headache!!..........


Very, very complete, I'm sure that with all of this, I can find the problem.


Best regards and Merry Xmas,

Bill
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