So I pulled out of the driveway and the engine died. Cycled the key and no fuel pump. Today I pulled the bed off checked for power at the fuel pump connector. While connected it has no voltage, unplug it and it has 12 volts. Checked voltage at the relay 12 volts unplugged, 0 volts connected at the orange and lt-blue wires. Did the same at the computer. Tried running a jumper wire from the relay back to the pump connecter, and nothing changed.

1990 with a 2.9
Here's the wiring diagram. any help would be appreciated.

 

Sounds like you've got an open or a short somewhere.

 

Fuel pump inertia switch?

 

i bypassed the inertia switch and replaced the relay

 

So you changed the relay? Did that change anything? I'm thinking no, the relay sounded like it wasn't the problem. I think you have a short somewhere.

 

no the relay didn't change anything. if there is a short, I can't find it. I ran a jumper wire from the relay output to the fuel pump power wire, bypassing all the factory wiring

 

could it be the computer? but computers rarely go bad.

 

When you unplugged the connector at the fuel pump was that the only thing unplugged? I'm starting to think the problem might be in the fuel pump itself.

 

yes it was the only thing unplugged, but I have another pump out of a previous truck and it does the same thing. it worked when i took it out, but it's been sitting for the past 3 years in my barn. Also, I can wire it directly to the battery and the pump will run. like I said, it's driving me insane.

Edit: the second pump did have 0.25V, but thats still nothing really.

 

You've got the electrical gremlins my friend.

 

ya, I'm thinkin I might call a family friend who's a mechanic, or take it to my advanced electronics class tuesday.

 

Thats probably the best idea. I really do think there is either an open or a short somewhere though. That explains the lack of voltage when plugged in. Good luck.

 

yeah, I agree. just wish I could find it.

 

If there was a short on the circuit it would blow the fuse in the PDB. Since it will run when jumped directly from the battery I would suspect a point of high resistance in the circuit. Have you tried replacing the relay? You also might want to check the fuse and its socket for signs of corrosion.

If you have an Ohm Meter try checking the resistance between the ORG-LT BLU wire with the relay unplugged and the PINK-BLK wire connector at the tank. Or you could try applying a jumper between the battery positive terminal and the ORG-LT BLU wire at the relay output and see if the pump will run. If it still doesn't run try jumping between the battery and the PINK-BLK wire under cab connector.

 

Problem Fixed!!!

So I took my truck to class today, popped the hood and my instructor found a loose ground connector partially unplugged within 5 seconds. Pissed that I didn't find it, but glad the problem was fixed. Turned out to be the ground connector for the pcm and eec relay.