Duh....

Actually I replaced the other relay (EEC) with the fuel relay (they fit)... just realized this.

I dug out the fuel pump relay and AHA... there is no relay, it was jumpered-- this would be why the pump never shuts off.

I placed the fuel relay in it's proper location, but as you might have guessed, the jumper wire was there for a reason. When I turn the key, no fuel pump at all, everything else functional. According to the haynes that I have, this relay is also connected to the inertia switch.

Does anyone have an idea why this would be jumpered? Could it be a bad inertia switch?

I will have a look later tonight, it sounds like there may be a short somewhere, when I turn the key I hear 3 snapping sounds. The truck will try to start, just no fuel.

 

The relay output goes through the intertia switch to get to the fuel pumps, so the intertia switch should be fine. The computer grounds the turn on lead for the relay, so test for continuity between the relay plug (leave out relay) and the computer fuel pump pin at the computer connector. Also test for 12V on the other side of that fuel relay plug (should have 12V on two wires with key on, third wire goes to the computer for turn-on, and the fourth wire goes to the inertia switch/dash tank selector switch, then to the fuel pumps).

 

Thanks for the tips, I will try in the AM.

Maybe I am (obviously) thinking about this wrong, but if the output from the relay goes first to the inertia switch, then the fuel pumps, why does that rule out the inertia switch? It seems like if the switch was bad and the power travels through it, that could be a problem?

Anyway, thanks again, I will start troubleshooting tomorrow.

Dan

 

The power will travel through the inertia switch until a sudden deceleration (crash) trips the inertia switch, interrupting the signal. If your fuel pumps run, the inertia switch is probably fine.

 

But I don't think my fuel pumps are running, I am not getting fuel since I replaced the jumper w/ the relay.

 

Yes, but since they ran when the relay was jumpered, I would think that for some reason the relay is not being switched on. It's a turn-on problem with the relay, either not getting power on the turn on lead, or not getting ground through the computer. If you jump hot 12V in to the out lead to the fuel pumps, they run, correct? That's what the relay should be doing, but for some reason it isn't getting the command to do so.

 

Ok I get it now! Thanks!

I have never done the continuity testing procedure, however it is covered in my haynes manual, seems pretty straight forward.

I will let you know how I do.

 

One more quick one. When I check for continuity between the fuel pump pin @ the connector and the relay plug, I should use a multimeter with one lead on each (with the power off) right?

 

That is correct. I'm not sure what meter you are using, but mine beeps when it senses continuity. If it senses continuity, it might also be a good idea to measure the resistance of the wire.

 

When I first got my 91 F250 it had the fuel pump relays jumpered. I found that the reason for this was that one of the wires that is on the starter solinoid had corroded at the ring terminal under the heat shrink.

 

I am only getting 12V to one of the wires of the four at the relay.

The red is 12V, According to Haynes, the tan w/ lt green wire goes to fuel pump and the EEC-IV self test connection, and the brown wire goes to the inertia switch.

That leaves the yellow wire, it goes to the electrical control assy (on pin 1) and also to the ignition. I presume this should see 12V with the key on, so I need to trace this connection.

I will check the solinoid, any other ideas on where to look?

 

Would the wire still be yellow at the solonoid?

 

Ok, I am fully stumped here. I replaced the EEC relay, it looked bad. No change.


When I turn the key, both relays click. The fuel relay is getting 12V @ the red wire, but not the yellow. I checked the solonoid, cleaned up the connections, and tested the wires, they all seem to be getting 12V

According to my haynes wiring diagram, the yellow wire goes to ignition and to pin 1 of a connector (I cannot seem to find this connection, in the haynes manual it looks like a long rectangular plug).

My ignition works fine, however I suppose that could still be a problem. Any ideas?

Sorry to keep throwing this out there, but I am stumped.

Does anyone have a better wiring schematic than the haynes?