Suspected Bad PCM

Reply Subscribe

Thread Tools

Search this Thread

Nov 5, 2004 | 09:02 AM

Izzy

Thread Starter

New User

Joined: Dec 2003

Posts: 12

Likes: 0

Suspected Bad PCM

Guys,
My fuel pump stopped working on my 1995 V6 4.0L and after some troubleshooting I feel that the PCM is not providing the ground to allow the fuel pump relay to pull in. I was wondering if it might be that the PCM is not getting a signal from some other device and that is the reason the fuel pump relay does not pull in. I would hate to replace the PCM and that not fix the problem. Any suggestion as to what the PCM is expecting before the fuel pump is allowed to engage?

James IZZY Isbell
1995 XLT V6 4.0L

also have
2004 4x4 V6 4.0L

Nov 5, 2004 | 11:00 AM

Dave257

Posting Guru

Joined: Jun 2003

Posts: 1,205

Likes: 0

when you turn the key on (not start) the relay should click on and the fuel pump run to build pressure. It is fed by another path, after it starts the pcm supplys the control to the relay. It should start for a couple of seconds and the die if it was just the pcm not controlling the relay.
Dave

Last edited by Dave257; Nov 5, 2004 at 11:02 AM.

Nov 5, 2004 | 11:31 AM

Izzy

Thread Starter

New User

Joined: Dec 2003

Posts: 12

Likes: 0

Thanks,
I guess maybe a clogged fuel filter could cause this porblem? When I turn the key on the fuel pump relay does not pull in at all. When I check the voltages at the relay I have the right 12V at the appropreate terminals but there is no graound for the fuel pump relay. I guess I could try and run a jumper to ground and see if the fuel pump comes on.

Nov 5, 2004 | 06:00 PM

wire4money

Senior User

Joined: Mar 2004

Posts: 140

Likes: 0

From: Sunriver, Or

did you check the inertia switch? it cuts power to the pump in the event of a crash.

Nov 8, 2004 | 09:04 AM

Izzy

Thread Starter

New User

Joined: Dec 2003

Posts: 12

Likes: 0

Ya I check it. I feel that maybe the fuel filter might be cloged and stopping the fuel pump from comming on. Do you think this might be it. The relay does not energize at all. So if the PCM is ok and the fuel filter is clogged maybe it wont allow the pump to come on?

Nov 8, 2004 | 12:08 PM

Dave257

Posting Guru

Joined: Jun 2003

Posts: 1,205

Likes: 0

A clogged fuel filter would not stop the fuel pump from running. Do you have a diagram of the fuel pump electrical circuit?
Dave

Nov 8, 2004 | 02:21 PM

Izzy

Thread Starter

New User

Joined: Dec 2003

Posts: 12

Likes: 0

Yes I have followed the circuit and the relay is provided a ground through the PCM this is why I felt that it might be bad. You mentioned that the fuel pump gets power from another loaction untill the engine is running and then it gets a ground from the PCM. The schematic shows that the fuel pump only gets its ground from the PCM. It doesnt show any other ground for the pump. I thought that maybe the fuel pump wont come on if the filter is clogged and the pump is up to pressure, I didnt get a chance to work on it this weekend. I will remove the filter and see if that fixes it because its the cheap fix. If that doesnt work I guess I will try to jumper the ground and see if the pump starts. Thanks fer your suggestions.