My 87 F350 460 let me down today, just quit running like it ran out of fuel. I could get it to start just a little and actually drove about a mile closer home before it quit for good. I'm not getting any fuel up to the carb, so it would seam no power to either pump. Anyone out there in FTE seen this before or better yet have helpful info on the stock fuel pump wiring so tomorrow I can work it out.

My guess would be somewhere in the wiring before the switch, I think the tank selector switch is still working. The guage switches it and wouldn't run on either tank. I can't hear the tank selector valve but never could on this truck. I could however get home by adding a pump up by the carb, so I can pull fuel thru the selector from the tank.

From what I remember I think I have both some kind of oil pressure switch and a fuel shut off in the system, along with a relay of cours though I have no idea where it is, anyone know much about these, like where the shut off and relay is?

Gotta get this truck fixed tomorrow any help is apprciated, thanks.

 

the fuel shutoff switch is on the inner firewall just forward of the clutch pedal. i dealt with one in a friend's truck that had gone bad. take a jumper wire and short out its 2 contacts and see if your pump runs then. also check for power there, it should be +12v. not sure where the relay is in these, but its before they all got smart and put them in a nice little box under the hood.

 

Power goes through the inertia switch in the cab. (there is a reset button)
The oil pressure sensor (not the gauge sender) closes to ground on the pulldown side of the safety relay.
From that relay power goes to the switching relay next to it.
And then, power goes to one or the other pump(s).

While cranking, power is sent from the starter circuit, through a diode, directly to the switching relay. (bypassing the inertia switch and safety relay, always providing the pumps with power, before oil pressure has built up)

Sometimes the relay(s) can check good but the underside of the socket is corroded.

HTH.

 

Thanks Jim, that's great then it can only be the relay , diode, or a broken connection. Cause no fuel during cranking, now the biggie, anyone know where it is, lol? Or wire colors for testing?

 

The relays *should be* mounted side by side up in the corner of the drivers side firewall.

There is a black & white schematic up in the 'Read First' sticky at the head of this section; https://www.ford-trucks.com/user_gal...d=182593&.jpg=

I've also seen one in color here... I think it comes from Subford.
Let me see if I can get a Google image.

 

Try this, click on the thumbnail and it will open full sized and in color.



You will see that the dash switch powers the selector valve, and when on the front tank, pulls down the selector relay.

I really think it must be a bad selector relay (or the socket!)
Because I doubt both the inertia switch AND the bypass circuit would go bad at the same time.

 

PURFECT Thanks a lot Jim that's exactly what I needed assuming when I can finally get to work on the truck I can find these componants. That said I agree it can really only be the relay or a bad connection. Otherwise it would pump during cranking.

EDIT; Wait that's not right, I see 2 power sources to the selector switch, and the cranking circuit doesn't go thru the relay. The fact that it's not pumping during cranking or run means either everything went bad all at once or it's in the selctor switch. It's the only common factor. So when I can get to the truck I'm going right to the selctor switch, popping that sucker out and jumping wires.

OK think I got enough wiring info, I'm still not %100 on the selector valve though, I think I saw 3 fuel line connections to it. But the system has a retern, so is the selector just switching the return and the pumps being on or off selecting the source?

 

Wait, relayS now in the black and white diagram I see one relay and one switch, and in the color a second relay and a significantly different wiring. Largely the addition of a tank selector relay, could the color be EFI and the black and white carbed?

 

Thanks for the help, I can finaly leave to go where the truck is to fix it. But no internet connection there, thanks to damn sprint. So I'll update when I'm done.

 

The B/W diagram is a basic circuit, Subford's color diagram is correct.

While I was out re-sealing my cowl today I noticed the two dimples in the area below the DS hood hinge where the relay bracket would screw to if I had the Hot Fuel Handling instead of a mechanical pump.

Don't forget to check those two blue fusible links at the starter solenoid, if you find you have no power going TO the inertia switch in the cab.

Good luck.

 

I tell ya I love my truck but sometimes what Ford does can really **** a guy off. They couldn't mount the fuel tank selector a foot further forward, not like there isn't plenty of frame rail. Nope they gotta mount it right between the frame rail, tank, and crossmember.

Anyway, I got it mostly fiqured, not completely fixed but running and on it's way to being completely sorted. Turns out I ran the rear tank dry and when I switched to the front tank the pump gave out. This of course was all made more possible by the state of this truck, I can't hear the pumps over the exhaust and the fuel level senders only kinda work. This was all made harder to figure by the wiring on this truck being a mess and certainly not working how it should based on the diagrams. In my truck the wire colors weren't whats in those diagrams. The wire at the inertia shut off or relay aren't hot all the time as it should be and putting power at the fuel shut off powered the pump on but shouldn't.

I'll look for a better wiring diagram tonight, and fix and figure out more tomorrow

 

Maybe these two diagrams below will help.
The color one linked to above is wired right but the wire colors have changed as the color one is for a 1983.




/

 

Thanks Bill, but again no go. That diagram looks like a better version of the black and white one Jim posted earlier. The difference between it and the color being that the color has a fuel selector relay, where the other 2 do not. But the wire colors and function still don't match my 87 .

Ok so the most clear difference is that at the inertia shut off the wires are small about 18ga, grey and red/yellow IIRC, and do not have constant power as they would in these diagrams. All diagrams here and I've found so far have the wires at the inertia shut off yellow on both sides and constant hot. There is power at the inertia shut off switch with the engine running, but not key on and putting power there powered on the fuel pump selector switch which then powered the fuel pumps.

I could only find two relays so far, one fuel the other clearly marked trailer wiring. The fuel has a green connector, the 2 heavy gauge wires are black and yellow the 2 smaller wires black and red or orange with yellow stripe. I need to do more checking on when what is hot on this relay.

At the selector switch is the only place some wires are the same, front tank is red, rear is brown/white, and ground is black. The power wire to the selector switch is red or orange with a yellow stripe.

Really I only know 2 things about how it's working, that putting power to the wires at the interia shut off powers on everything wether or not the key is on. And that there is power there with oil pressure but not ignition on. I think the oil pressure switch and inertia shut off switch are in line with each other on my truck. That both must be closed for the relay to be tripped. Where the relay I gets it's power and where that power goes before reaching the selector switch I do not know yet. I think there is a relay missing that I haven't found yet.

 

interesting. that does sound like another relay up the line somewhere. i can think up a simple redneck fix using a relay and a bit of wire, simply bringing power to the correct side of the shutoff switch, and i could probably have it installed in not more than an hour - but its better if we can figure out what really went wrong here...

 

Okay, you're saying that the oil pressure switch closes (engine running) to provide power to the inertia switch.
And... the selector works and the pumps run if you apply power directly to the inertia switch.
BUT, you still can't get the pumps to run, even with the engine running?