The fuse is good as long as im looking at the right one, and the fuel shut off switch apears to be working. No power at the fuel pump though.

I just bought this truck and the previous owner manualy wired the fuel pump through a switch from the battery under the hood. Im trying to get the original stuff to work but i need a wireing diagram to get it fixed.

any body have a wiring diagram handy? I need to know where the fuel pump power comes from and where it goes so i can test for breaks in the line


THanks.

 

Where are the fuel pump relays located?

 

http://i54.photobucket.com/albums/g9...nelwithkey.jpg located in the engine compartment. Driver's side on top of the inner fender liner.

Compliments of subford. Snagged it from another forum: 1994 f150 no start only getting 7 volts to the fuel pump, - Ford F150 .net

 

check the wiring to the relays and where the relays plug in for corrosion/broken wires

 

Thats what happened to me no power to my pumps ran down to the junkyard through a relay in. Worked ever since

 

Okay UPDATE!!!!

i have 6.52v at the fuel inertia shut off switch. So im getting something. Actually bothers me more. Rather have full voltage or none at all. Partial voltage seems a bit weird.

I still have no voltage at the two wire to the fuel pump. And when i ohm test each of them i get an open to ground. and when i ohm test between the red and black i get 0.001 resistance.

This seems weird. There shouldn't be any continuity between them should there?


I checked the relays and switch them around. They all click when i put them in the horn relay spot and hit the horn.


What is weird is that i lost power to the inertia switch when i pulled the supposed ECM relay and didnt loose power when i pulled the fuel pump relay. What is up with that. Im going by the wiring diagram posted above.

 

Have you checked the connectiona at your computer? Do you still need that schematic?

 

The supply side of the Fuel Pump relay is always hot and should measure at whatever battery voltage you have. All fuel pump related supply voltages are referenced to ground. The Load side of the Fuel Pump relay goes to the PCM and the inertia switch.The PCM Power relay feeds the coil side of the Fuel Pump relay.

Use the link from the thread I posted. Halfway down the first page subford attached a wiring diagram. The OP who originally posted the thread has the exact same symptoms as yours, i.e. no fuel pump power AND it measures ~7V with a DVM. The voltage you are measuring is probably induced voltage because a wire is open. A digital DVM has a very high impedance. It does not load the circuit like a low impedance pump or a simple test light. Been there, done that and earned myself a beer proving that theory to someone before.

 

yes i think a schematic should help. I have some power to the ineria switch, so i doubt its computer related. either the relay is open or closed, cant really be half way.

 

seems that maybe i need to load the system to get an accurate voltage reading? at the inertia switch?

 

Do u have a chexk engine light with the key in run and the motor off?

 

Like RLA2005 just mentioned the activation is ground activated. Meaning, your fuel system does not operate, until the Computer supplies the ground. If you have checked the inertia switch and the relays, you have narrowed it down to wiring and computer. Double check the link posted above and you should find your schematic.

Good Luck!

 

Seems to be a broken wire near the pump, i have made a few small nicks in the positive line down the frame rail and had 11.2-12v up to near the end.


Funny question though, why do i still only have 6.9v at the inertia switch and have 12v down the frame?

 

Well now i did it. I had the problem solved, i had to replace a section of wire down the frame rail. I was wiring the fuel pump back in right above it, and i had the key on. (forgot it was on)

Anyways dropped my power cord and it grounded out to the frame and popped a fuse and something else i guess. I replaced the fuse and it popped a few more fuses each time i tried to turn the key on.

Now i dont have any power to one of the relays. Apparently there is more than one relay tied to the fuel system. It is the relay that is outside the fuse box. I have no power going to it at all. But i still have 12v to across the fuse. I also know all the relays are good. Apparently my relay that is in the fuse box is not getting signal to open.

 

12v across a fuse means it is open.