PCM for FOrd F150
 

DOes anyone know how to check to see if your PCM is bad? I was driving and the truck died. I am not getting power to the fuel pump and I followed the wire back to the PCM. ANy ideas?
Jerry

Welcome to FTE jmg12. :-X25

The PCM supplies ground for the pump to operate. Power to the pump is via a 20A fuse (F10) in the Battery Junction Box (BJB). The fuse supplies power to the Fuel Pump Relay which is also in the BJB (301). The relay supplies power to the Inertia Fuel Shut Off (IFS) switch. The IFS supplies power to the fuel pump. The power wire is Pink/Black. Good luck! :-wink

Hmmm, musta read that one out of AllData?? Just check the pump fuse and both wires at the IFS switch for voltage then get back to us..... You could also manually ground the pump and see if it runs. Unhook the pcm harness and use a computer safe(low resistance) test light to ground the wire from the fuel pump and see if it runs. I don't have the schematics in front of me and i don't remember how the circuit is set up...

Try a new fuel pump relay first. My truck quit when my relay went out. I've replaced my pcm too. My pcm was fried by a senser that shorted in the fuel tank. My truck ran bad but it never quit when the pcm was bad. It would throw all kinds of false codes &stall out sometimes. When it stalled I could restart it & it would run ok. I think only a dealer can test the pcm.

the dealer doesnt test the pcm, the dealer does tests around the pcm to determine what is going on.

heres what you need to do:
swap fuel pump relay with a similar one, see what happens.
if still no start- check terminals on fuel pump relay, you should have 2 powers and 2 grounds. The PCM switches to ground to activate the relay.
If you have 2 power terminals, you either have a bad ground or a bad pump.

IF you are good, you can jumper the power to the fuel pump with a jumper wire, it goes diagonally in the relay center, not to the one closest. You are going to want to figure out which is to the fuel pump and which is to the pcm.

I think that on a lot of trucks the fuel pump/sending unit is actualy grounded to the chassis.

BUT, since you arent getting power...

You could (for safteys sake) unplug pcm, unplug fuel sending unit, jumper both wires across, and that way for sure 1of them should send you power to the sending unit.

If you get power then, you either have a bad wire between the relay center and the pcm, or a bad pcm. If you are REALLY good, you could figure out which terminal on the relay center runs the wire to the pcm for the relay ground, then check it for continuity with an ohmmeter.