Is there a way to test the PCM? My friends truck keeps blowing the #18 fuse in the power distribution box. I have disconnected the O2 sensors, IAC, Map sensor, fuel pump relay, PCM relay and the PCM. The only time the fuse won't blow when turning the ignition is when the PCM is disconnected. The low beams, wipers and radio are not working as well. Any ideas on what to check??

 

Sounds like a short to ground, (I'm master of the obvious, I know) and not the PCM. What circuit exactly is fuse 18? I'd start underneath the truck, and check the wiring.

 

PCM, fuelpump relay, mass airflow sensor. I have checked the wires to the O2 sensors and every other wire I can find for a short but I have not found one. Just before the truck quit running, the wipers came on, the headlights flashed, and the radio quit. He heard what sounded like a pop sound and it died. It will crank but won't start. The battery top was also popped up from the case on one side.

 

Change the battery, check the cables, and then check the alternator cables. The only thing that could possibly do that to a battery would be the alternator.

Or lightining, or a power pole wire hitting the truck in a tornado, hurricane, or earthquake.

 

The battery was replaced. We unplugged the alternator and still blew the fuse when the key was turned.

 

What year truck and what engine /trans are you working on?

 

2004 F150 with a 4.2l and auto tranny.

 

bump it up

 

So is this by any chance a "Heritage Edition" old body style 2004 F150?

 

It's not a Heritage Edition but it is an old body style. Why do you ask?