I have a 97 4.2 F-150 and I have a short somewhere & it keeps blowin the PCM Power Fuse. At the suggestion of someone we unhooked the inertia switch and the fuse didnt blow, so then we hooked that back up and unhooked the fuel pump and the fuse didn't blow, so then we hooked the fuel pump back up and unhooked the wiring under the intake and still it did not blow, but we hooked that back up then the truck started. My question is has anyone had this problem before and if so can they say which wire was it specifically? Also was this a good method to find the Short?
I would trace the 12V (switched and unswitched) wiring from the fuse box to the PCM connector. The PCM does not SOURCE any current into the fuel pump circuit. The PCM SINKS current from the Fuel pump relay to pick it (close contacts).
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Did it blow a fuse in the fuse box under the hood? I don't have a 97 diagram, but the 99 diagram for a 4.2 shows several different fuses that power the PCM circuits, but there is only one that feed the computer itself. Which fuse is blowing?
And it's obvious from your experimentation, you have moved the wiring around and temporarily fixed the problem. I would go over the engine wiring with a fine tooth comb and see if you can find any bare spots.
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