Another PCM Fuse Blowing Thread.. 2001 Mustang Cobra

foofinator

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Dec 24, 2017
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First, thanks for all of your help on this project. With it, I have been able to go from this (when it arrived from the auction):

Before.PNG


To this (though it was waiting on the tow truck after its most recent issue):

after.PNG


This is a car I bought from Copart a few years ago and have been restoring. It's got new interior, a new top, new paint, a new transmission, and new front and rear suspension to name a few items. The last thing to tackle is the engine (which is still in as "good" of shape as the before picture), and the plan is to finally install the On3 Performance turbo kit that has been sitting on my shelf for awhile.

It was running awesome until recently, when the PCM fuse started to blow. I've read all of the PCM threads and believe that I checked the common issues, but it was to no avail. This included a thorough visual inspection of the engine wiring harness, including the capacitors on the backs of the cylinder heads, COP wiring, injector wiring, and MAF wiring. That inspection turned up a horrible ECT pigtail with no insulation and an oil pressure sensor pigtail in the same state. It does not seem that the ECT or oil pressure sensor pigtails are causing the issue, because I can purposefully short them with the key on and the PCM fuse does not blow. Also, since the problem is intermittent, I set the fan to run at the lowest temperature possible in the tune; the low and high speed fans came on as instructed, and the fuse did not blow. Finally, the car has brand new Ford COPs.

Any ideas on how to approach this issue?

Another issue the car has, but I do not think it is related, is that it takes several seconds for the car to start. I can alleviate this issue by keying on and off to build pressure in the fuel system, so I suspect a bad drain-back valve. The plan was to live with this until the engine build, when I'll be installing a new fuel system anyway.

Thanks in advance.
 
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foofinator

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Dec 24, 2017
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Update. I got a little more aggressive with the harness in my last inspection, and the insulation on one of the noise suppressors on the back of the head fell apart. I don't see how it could short to ground, but I forced it to do so and the PCM fuse blew. Maybe this is my problem.
 

foofinator

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Dec 24, 2017
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Well, was fixed for awhile. Blew the PCM fuse again and had to ride the tow truck. It's odd because it's intermittent. It also only seems to happen when the engine is warm.

Any thoughts?