88 F150 PCM/Fuel Problem
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88 F150 PCM/Fuel Problem
My truck stopped suddenly in a parking garage and I could not get it towed that night, so I went back early the next morning (with my Haynes manual) and found that by using the diagnostic port I could get the fuel pump to actuate and the truck to run. I was looking at it more and there appears to be a FET on the PCM that controls the relay and it does not appear to be doing its thing. The PCM is kind of expensive - are there any sources for schematics and replacement parts list for the PCM so that I can try to repair it?
Lead Driver
Joined: Aug 2006
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From: Sand Lake, MI
Can you hear the fuel pump's relay "click" when the key is turned on?
Did you try a new relay?
Not sure, I'd have to look it up to see if the diagnostic port bypasses the pumps relay or not.
Did you hear it click when powering the pump that way?
Now that I think about it I think the Dia. port grounds the relay bypassing the computer.
Did you try a new relay?
Not sure, I'd have to look it up to see if the diagnostic port bypasses the pumps relay or not.
Did you hear it click when powering the pump that way?
Now that I think about it I think the Dia. port grounds the relay bypassing the computer.
Last edited by danr1; Dec 27, 2007 at 04:17 PM.
Fleet Owner
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From: Easton,Ks
I have heard of your symptoms before but I have not heard of a replacement PCM Computer fixing it.
When the Computer fails it has always worked the other way, the pumps stay on.
First I would check the small black wire with a green stripe coming off the negative post of the battery and make sure it is well grounded to the post.
If that is not it remove the battery negative post cable and unplug the PCM computer plug and make sure all of the pins are OK and then plug it back in, put the cable back on and see if it is OK now.
If not check the PIP wire from the PCM computer to the ICM module (TFI). Also check the SPOUT wire and make sure it is not grounded.
When the Computer fails it has always worked the other way, the pumps stay on.
First I would check the small black wire with a green stripe coming off the negative post of the battery and make sure it is well grounded to the post.
If that is not it remove the battery negative post cable and unplug the PCM computer plug and make sure all of the pins are OK and then plug it back in, put the cable back on and see if it is OK now.
If not check the PIP wire from the PCM computer to the ICM module (TFI). Also check the SPOUT wire and make sure it is not grounded.
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More Info Please
danr1: Yes, the diagnostic port still activates the relay and is dependent upon the inertia switch, so I guess I am not too concerned in driving it with the diagnostic port grounded. The relay and pumps do not activate until I ground the diagnostic port connector.
subford: I am working from a haynes manual and it does not identify a PIP or SPOUT connector. For the 4.9L engine, the manual does not show a high pressure pump in the circuit but it appears to be there. My manual shows 3 wires from the PCM to TFI: YEL / LT GRN, DK BLU, and BLK / ORG. Can you give me PCM connector numbers or anything more for the PIP and SPOUT lines?
Thanks
subford: I am working from a haynes manual and it does not identify a PIP or SPOUT connector. For the 4.9L engine, the manual does not show a high pressure pump in the circuit but it appears to be there. My manual shows 3 wires from the PCM to TFI: YEL / LT GRN, DK BLU, and BLK / ORG. Can you give me PCM connector numbers or anything more for the PIP and SPOUT lines?
Thanks
Fleet Owner
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From: Easton,Ks
Originally Posted by wroseland
subford: I am working from a haynes manual and it does not identify a PIP or SPOUT connector. For the 4.9L engine, the manual does not show a high pressure pump in the circuit but it appears to be there. My manual shows 3 wires from the PCM to TFI: YEL / LT GRN, DK BLU, and BLK / ORG. Can you give me PCM connector numbers or anything more for the PIP and SPOUT lines?
Thanks
Thanks
/
Last edited by subford; Dec 29, 2007 at 09:10 AM.
Fleet Owner
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From: Easton,Ks
Yes he was just grounding pin #6 of the DLC test connector.
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