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Dead PCM ?

D

dktool

NAXJA Forum User
Location
Covina
My '98 Fed model suddenly developed a no fuel pump relay power on -time out function, there for no ticky no runny.

I swapped relays, checked fuses etc.
If I wire a switched hot lead to the O.N. output side of the relay base, the pump turns on and everything if fine until I turn the McGyvler switch off, then the pressure drops and it dies.

The Chrysler p/n on my PCM is: P56041 with another number in bold print: 534AF
I have found some on ebay that have the correct first series of numbers but the second series varies from what mine is, is this just a production code or ??

Anyone have a quick good local source for the PCM ?
Does it sound like my diagnosis is good ?

Thanks
 
dktool said:
My '98 Fed model suddenly developed a no fuel pump relay power on -time out function, there for no ticky no runny.

I swapped relays, checked fuses etc.
If I wire a switched hot lead to the O.N. output side of the relay base, the pump turns on and everything if fine until I turn the McGyvler switch off, then the pressure drops and it dies.

The Chrysler p/n on my PCM is: P56041 with another number in bold print: 534AF
I have found some on ebay that have the correct first series of numbers but the second series varies from what mine is, is this just a production code or ??

Anyone have a quick good local source for the PCM ?
Does it sound like my diagnosis is good ?

Thanks
Click to expand...

The last 3 digits are the calibration ID and the last two letters are the revision of the calibration ID.

fuelpump.jpg

This is your fuel pump diagram, so with the key on engine off you should have power on relay pins 2 and pin 4 and when the ecu is commanding the fuel pump you should see ground on pin 6.

pdc.jpg


You should also check for continuity between pin 6 on the relay and connector C3 pin 19 on the ECU.

ecu.png
 
Does your CHECK ENGINE light come on and the fuel pump prime when you pass the key to RUN? Not sure if this is the same with your year but on my 93 XJ I had the following problem.

When my PCM started to go bad I would pass the key to RUN and neither the CHECK ENGINE light would come on or the fuel pump prime.

If I left the key on RUN after about 5 seconds both the light would come on and the pump would prime. It gradually got worse and I would have to leave the key in RUN for 30 seconds. If I just cranked the engine over it would not start. That's when I changed the computer and all worked ok after.

Patrick
 
The check engine light does come on when the key is "on" but the pump relay never primes regardless of time allowed.
 
sidewaysstarion said:
The last 3 digits are the calibration ID and the last two letters are the revision of the calibration ID.

fuelpump.jpg

This is your fuel pump diagram, so with the key on engine off you should have power on relay pins 2 and pin 4 and when the ecu is commanding the fuel pump you should see ground on pin 6.

pdc.jpg


You should also check for continuity between pin 6 on the relay and connector C3 pin 19 on the ECU.

ecu.png
Click to expand...

I checked for voltages and continuity as instructed above.
Everything checks out correctly, the only missing part of the puzzle is the lack of a negative / ground signal from pin #19 on C3

I rigged up a toggle switch in the cab to supply a ground source for the relay, pin#6 and all is well until I find a replacement PCM

Thanks for the help, now go find me a PCM :cheers:
 
dktool said:
I checked for voltages and continuity as instructed above.

Everything checks out correctly, the only missing part of the puzzle is the lack of a negative / ground signal from pin #19 on C3

I rigged up a toggle switch in the cab to supply a ground source for the relay, pin#6 and all is well until I find a replacement PCM

Thanks for the help, now go find me a PCM :cheers:
Click to expand...
How are you determining that there is no negative/ground signal from pin 19 on C3?
 
Sidewinder CC said:
How are you determining that there is no negative/ground signal from pin 19 on C3?
Click to expand...

I unplugged C3 and checked continuity from (socket) 19 to (socket) 6 at the relay base.

If I really wanted to be extra anal I could snake a lead out of the C3 pin 19 and verify it is dead (no -) when running, or I could ground the C3 19 socket with the key turned on and the relay would make, but those extra steps are unnecessary.

It is currently running 100% normal with the temp-ground switch set up.
I am shopping for a replacement PCM so if anyone has a good lead on one, let me know.

P/N P56041 534AF
 
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