1998 B4000 4.0 OHV - PCM not powering up

[snardos]

I've been working on my Dad's truck for that last week. He was driving it when it when the engine light came on and it stalled. Once he stopped he was able to restart it but it stalled again and wouldn't restart. To clarify it does crank but does not run.

The first thing I tried was to scan it since he said the engine light came on when it stalled. I wasn't able to communicate with the computer at all and I realized that the engine light wasn't coming on when the key was turned on. The fuel pump also wasn't running, but it works fine when I jump the fuel pump relay. I started checking fuses: all good. I checked the relays: also good.

I got a wiring diagram and started checking power at the PCM.

I have power at all the connections that are supposed to have power: Pins 97, 71 are getting power from the PCM Power relay. Pin 55 is getting constant power.

I also have ground at all the connections that are supposed to have ground: Pins 24, 25, 51, 76, 77, and 103.

Of course I assumed the PCM might just be bad. It just so happens I also have a vehicle with EEC-V. I took the computer out that I assumed to be bad and put it in my truck and I was able to communicate with it just fine.

Is there anything I am missing that requires these EEC-V PCMs to power up? I feel like i'm going crazy.

 

[martin]

Might be irrelavent in this case but I've seen vehicles that refuse to scan when the fuse for the cigarette lighter fuse is blown.

 

[snardos]

I'm pretty sure I checked that fuse already, but I will check it again next time I'm over there.