GEN 1 Fuel pump relay fuse blows when key is inserted.

[dc17172]

If electrical devices "shorted" at the actual rate that people declare them to, this country would be an inferno.

Thanks, I'm glad that's not the case!

 

[FordTechOne]

Thank you for that insight. I hate throwing parts at a problem but I was at a loss. If I don't have to, I certainly won't. Do you know any common failure points in the wiring? Or do you have any suggestions as to where I should start looking?

Start by inspecting the FPDM. It’s located on a frame crossmember toward the rear of the truck. Due to its location, it’s exposed to moisture, corrosion, dirt, debris, etc. Check the module itself as well as the harness and connector.

 

[dc17172]

Start by inspecting the FPDM. It’s located on a frame crossmember toward the rear of the truck. Due to its location, it’s exposed to moisture, corrosion, dirt, debris, etc. Check the module itself as well as the harness and connector.

Sta myrt by inspecting the FPDM. It’s located on a frame crossmember toward the rear of the truck. Due to its location, it’s exposed to moisture, corrosion, dirt, debris, etc. Check the module itself as well as the harness and connector.

View attachment 422358

I have already replaced the module itself. I'll inspect the harness and wires leading up to it. Thanks you!

 

[dc17172]

The FPDM and connector is fine. I inspected it and the connections appeared good. I unplugged the FPDM and inserted the key and it blew the fuse again. I did notice the ground wires on the crossmember are a bit weak and rusted. I'm going to address it tomorrow. Hopefully that is the culprit. Here's a picture of the ground.

 

[dc17172]

UPDATE:

I have tracked the fuse-popping culprit to a purple-tealish wire coming from the fuel pump relay in the fuse box. I can't figure out what the purpose of the wire is. I could not find and breaks or corrosion on the wire. I did cut it for diagnostic reasons and it no longer blows the fuse. The truck will not start with it cut. I'm hoping someone has the pin-out and wiring diagram for the fuel pump and the fuel pump relay. Thanks

 

[rschap1]

Congrats on the detective work so far.
Good luck with the repair

 

[FordTechOne]

UPDATE:

I have tracked the fuse-popping culprit to a purple-tealish wire coming from the fuel pump relay in the fuse box. I can't figure out what the purpose of the wire is. I could not find and breaks or corrosion on the wire. I did cut it for diagnostic reasons and it no longer blows the fuse. The truck will not start with it cut. I'm hoping someone has the pin-out and wiring diagram for the fuel pump and the fuel pump relay. Thanks

The violet wire with a green tracer is the power feed to the fuel pump control module. It also supplies power to the fuel injectors, so if an injector or circuit is shorted that will also blow the fuse. You can split up the circuit for testing purposes by disconnecting C1581 and/or C1010 to isolate the shorted circuit or component.

 

[dc17172]

The violet wire with a green tracer is the power feed to the fuel pump control module. It also supplies power to the fuel injectors, so if an injector or circuit is shorted that will also blow the fuse. You can split up the circuit for testing purposes by disconnecting C1581 and/or C1010 to isolate the shorted circuit or component.

Man, I can't thank you enough. I'm on my way home to diagnose more. I'll update later. Thank you so much!

 

[CleverGirl_]

Man, I can't thank you enough. I'm on my way home to diagnose more. I'll update later. Thank you so much!

You'll see why everyone tags him for help. He's THE guy.

 

[dc17172]

He seems to be a master of his craft for sure. I'm grateful he shares his knowledge!