Fuel Issues.

[jmadigan]

The fuel pump cutoff relay. What bothers me is the way things are hooked up now the pump should be running even with the key off. The fact that it isn't makes my suspect that there is an open circuit somewhere between the blue fusible link and the tank selector relay.

Fuse link T is the blue fusible link, the way it is connected, the pink with a black hash wire should have battery voltage through the diode to the relay socket, you should also have power at the fuel pump cutoff relay https://forum.garysgaragemahal.com/file/n113317/Fuel_pump_cutoff_relay_terminals.jpg

640, Red with Yellow Hash is powered by the oil pressure switch when closed; 57, black is ground; 37, Yellow is powered directly from the battery through the inertia switch (inside on the heater duct, passenger side); 787, Pink with Black Hash, is powered when the relay coil is powered by the oil pressure switch. If the power is on circuit 787, then the pump will run.

You need to check these items and figure out how hosed up the wiring is ( maybe) and then work on correcting it.

All of this checks out pink with black has power when running

 

[jmadigan]

Yes sir, that is correct. Are you comfortable following a wiring diagram? I posted them earlier, it is in two parts, one follows the gauge system wiring, the other the fuel pump power. If you unplug the yellow wires at C144 with the blue fusible link still on the hot side of the starter relay, there should be battery voltage there. If not then there is a problem with the fusible link. Look for a melted area and gently tug on the ends. If there is a melted area, that's the problem.

If you have battery voltage there, try jumping the pins in the male side of C144 and see if you hear a pump run and a hiss from the vapor separator. If that works, then go under the passenger side of the dash, on the heater duct, you should see two yellow wires plugged into a switch with a push button on top, push down on the button and see if it clicks and stays down.

If jumping the pins in C144 doesn't work, then move over to the relay under the shield on the driver's side firewall. Check first for battery voltage at the pink with black hash wire, this is the feed from the blue fusible link. If you have battery voltage there with the relay plugged in, then you will need to check for battery voltage at the yellow wire first, then the red and the brown with white wires, one should have power, if not the relay is bad. If you do not have power at the pink with black hash wire, then the diode may be open or the wire may be broken.

If you find the tank selector relay is bad, a standard Bosch cube relay will functionally replace it with a socket. If it is exposed under hood, seal the back side of the socket with RTV.

All of this is fine 13 volts while running maybe I’m chasing ghost problems. I’ve heard there may be check balls in the pumps to keep the pressure from bleeding off is this correct?

 

[jmadigan]

Yes sir, that is correct. Are you comfortable following a wiring diagram? I posted them earlier, it is in two parts, one follows the gauge system wiring, the other the fuel pump power. If you unplug the yellow wires at C144 with the blue fusible link still on the hot side of the starter relay, there should be battery voltage there. If not then there is a problem with the fusible link. Look for a melted area and gently tug on the ends. If there is a melted area, that's the problem.

If you have battery voltage there, try jumping the pins in the male side of C144 and see if you hear a pump run and a hiss from the vapor separator. If that works, then go under the passenger side of the dash, on the heater duct, you should see two yellow wires plugged into a switch with a push button on top, push down on the button and see if it clicks and stays down.

If jumping the pins in C144 doesn't work, then move over to the relay under the shield on the driver's side firewall. Check first for battery voltage at the pink with black hash wire, this is the feed from the blue fusible link. If you have battery voltage there with the relay plugged in, then you will need to check for battery voltage at the yellow wire first, then the red and the brown with white wires, one should have power, if not the relay is bad. If you do not have power at the pink with black hash wire, then the diode may be open or the wire may be broken.

If you find the tank selector relay is bad, a standard Bosch cube relay will functionally replace it with a socket. If it is exposed under hood, seal the back side of the socket with RTV.

All of this is fine 13 volts while running maybe I’m chasing ghost problems. I’ve heard there may be check balls in the pumps to keep the pressure from bleeding off is this correct?

I’m really contemplating just adding a 2 way momentary switch to prime from each tank before I crank on it. Can I tap into the brown/white and red wires at the relay to accomplish this?

[85lebaront2]

I’m really contemplating just adding a 2 way momentary switch to prime from each tank before I crank on it. Can I tap into the brown/white and red wires at the relay to accomplish this?

Running obviously wasn't the problem, it was the starting priming circuit. If everything was working correctly, the way you had it wired, blue fusible link to battery, the pump would be running even with the key off.

You were asking earlier about getting the wires out of the relay sockets, so here it is in pictures, I am using the brown socket which I believe would be your fuel pump cutoff relay (wire colors are wrong as this is from a 1990 F250, EFI 460)

First, the relay socket top and bottom:

Note the thin slot left side top, this is where I insert a metal nail file to push up on the retainer tabs:

Once the retainer is lifted enough to put a small pick or screwdriver under it simple work it out.

If you look carefully at the retainer, some of the tabs have small hooks, these are what keep it in the socket. With the retainer out, each terminal has a plastic latch that holds it in place, push the latch away from the metal terminal until the terminal can be moved away from the retainer area.

 

[jmadigan]

Running obviously wasn't the problem, it was the starting priming circuit. If everything was working correctly, the way you had it wired, blue fusible link to battery, the pump would be running even with the key off.

You were asking earlier about getting the wires out of the relay sockets, so here it is in pictures, I am using the brown socket which I believe would be your fuel pump cutoff relay (wire colors are wrong as this is from a 1990 F250, EFI 460)

First, the relay socket top and bottom:

Note the thin slot left side top, this is where I insert a metal nail file to push up on the retainer tabs:

Once the retainer is lifted enough to put a small pick or screwdriver under it simple work it out.

If you look carefully at the retainer, some of the tabs have small hooks, these are what keep it in the socket. With the retainer out, each terminal has a plastic latch that holds it in place, push the latch away from the metal terminal until the terminal can be moved away from the retainer area.

The blue wire is not on battery power I have it wired to the “I” post on starter relay it was originally on the big lug that goes to the starter. If I measure voltage on the “I” lug I have nothing. When I crank the truck I get 12+v on this lug. I measured voltage on the pink and black wire I get 13 when running yellow I get 13 while running red and black 13 while running red 13 brown and white 13 if I unplug the inertia switch it cuts dies as it should all my wiring seems to be functional are these measurements correct?

[jmadigan]

The blue wire is not on battery power I have it wired to the “I” post on starter relay it was originally on the big lug that goes to the starter. If I measure voltage on the “I” lug I have nothing. When I crank the truck I get 12+v on this lug. I measured voltage on the pink and black wire I get 13 when running yellow I get 13 while running red and black 13 while running red 13 brown and white 13 if I unplug the inertia switch it cuts dies as it should all my wiring seems to be functional are these measurements correct?

Actually hold on I did try blue wire hooked directly to battery side of relay and never got a pump. I also ohmed out the blue fuseable link and got 0 ohms so now I am thinking that wire is shot.

[jmadigan]

Actually hold on I did try blue wire hooked directly to battery side of relay and never got a pump. I also ohmed out the blue fuseable link and got 0 ohms so now I am thinking that wire is shot.

It just hit me that I would still see voltage because the resistance wire is tied into this wire. That’s why there is a diode… so this means I need to find a new fusable link. Can I just splice a new fusable link in before the diode or do I need to source a whole new wire?

[85lebaront2]

It just hit me that I would still see voltage because the resistance wire is tied into this wire. That’s why there is a diode… so this means I need to find a new fusable link. Can I just splice a new fusable link in before the diode or do I need to source a whole new wire?

Yes, the diagram gives the size, just be sure to connect it to the "I" terminal.

[jmadigan]

Yes, the diagram gives the size, just be sure to connect it to the "I" terminal.

Thank you I’ll give this a shot and report back it will be a few days and thank you for showing me how to get those connectors apart it was a mystery to me

[85lebaront2]

Thank you I’ll give this a shot and report back it will be a few days and thank you for showing me how to get those connectors apart it was a mystery to me

No problem, I completely redid the wiring on my truck, everything is pretty much 1996 now I learned how to get them apart, the ones that do come apart.

Before you go looking for a fusible link, see if you can find the diode in the harness, Ford eliminated them in the newer trucks so it may have been a high failure item. If you can locate it, jumper it across and see if the priming function works then. If it does, you're good to go with it.