My 99 E150 4.6 work van randomly blows the PCM fuse. I can drive it for 50 miles sometimes and it will blow the fuse and keep blowing it until it sits for a while then starts right back up. It even has blow before and I replaced the fuse and it starts right up and drives another 50 miles. I've disconnected just about everything I could while it was blowing the fuse and found nothing. I've pulled the fuse box apart and it looks fine.

Any help would be appreciated as this van is how I make a living.

I need the wiring diagram for the PCM circuit. I bought the Haynes manual but as usual they're no help.

 

Welcome to the site.

Theres actually 2 fuses that supply power distribution for the PCM power relay function.
Is it the 30 amp in the Battery Junction Box ? or the 30 amp in the Central Junction Box that blows?

 

I had the same issue with my e 250 and it was a ground issue on the o2 sensor grounding it's self on the engine block just before it exits the main wire bundle. Once we fixed that the issue stopped completely. When you take off the dog house it will be the aqua connector close to the driver side. Check that entire area because it rides against a bolt head that is the culprit.