Bad New PCM?
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Bad New PCM?
Hello FTE! I'm wrenching on a 1993 F150 with a 300 and e4od. The truck has sat a couple years but turns freely and ran when parked (other than the trans). I wasn't getting power to the fuel pump. I figured after a couple years of sitting in varnish might as well replace it as I clean the tank.
Moved relays around, checked fuses and all was right with the world. Pulled the ECM and had some nasty capacitors also couldn't pull codes so I ordered a refurbished unit from Rock Auto.
Now with a new fuel pump and ECM I still don't have juice to the pump. I broke out my Power Probe and have 12V to the fuel pump at the relay, I have ground to trigger the relay when pin 2 and 6 are jumpered at the EEC plug, and the pump runs if I put 12V to the business side of the relay.
Here's the rub, I don't have 12V to power the relay itself at the fuel pump or ECM relay. I pulled the fuse box up and the connections seem solid. Is there a fusible link somewhere that's responsible for this voltage supply? Is it routed through the ECM as well?
Moved relays around, checked fuses and all was right with the world. Pulled the ECM and had some nasty capacitors also couldn't pull codes so I ordered a refurbished unit from Rock Auto.
Now with a new fuel pump and ECM I still don't have juice to the pump. I broke out my Power Probe and have 12V to the fuel pump at the relay, I have ground to trigger the relay when pin 2 and 6 are jumpered at the EEC plug, and the pump runs if I put 12V to the business side of the relay.
Here's the rub, I don't have 12V to power the relay itself at the fuel pump or ECM relay. I pulled the fuse box up and the connections seem solid. Is there a fusible link somewhere that's responsible for this voltage supply? Is it routed through the ECM as well?
Fleet Owner
Joined: Aug 2005
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From: Easton,Ks
The power to power the PCM Power relay coil comes from the Ignition Switch. This is the same power circuit the puts power on the Ignition Coil.
The PCM power relay powers the coil of the fuel pump relay and the PCM Computer.
In 1993 it is called a PCM in the wiring diagrams and not an ECM.
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The PCM power relay powers the coil of the fuel pump relay and the PCM Computer.
In 1993 it is called a PCM in the wiring diagrams and not an ECM.
/
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Thanks for that diagram, it helped a lot in wrapping my head around this. I replaced the ignition switch as I wasn't getting power through it.
Now with the new switch there is still no power to the PCM relay in start/run. In key positions off or aux there is 12V to the relay. Would this indicate wires crossing/shorting somewhere? I just want to be sure before I pull the harness apart and start digging.
Now with the new switch there is still no power to the PCM relay in start/run. In key positions off or aux there is 12V to the relay. Would this indicate wires crossing/shorting somewhere? I just want to be sure before I pull the harness apart and start digging.
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