So I'm finally back to working on this 1986 F-250 with a 460 again. I bought a new carb for it and have been having the dreaded fuel problem. The truck starts and runs great, which tell me that the initial fuel system is working correctly, the one that by-passes the oil pressure safety switch and the other relay's. But once it's actually running it only last's for a couple of minutes. I've replaced the fuel pump cut off relay and have the oil pressure safety switch jumped to rule out both of those. I've been following the diagram on this site to try and find everything, the fusible link is still good and the inertia switch is good as well. I've reset the pump cut off switch and nothing changed there either. But what's getting me is in every diagram they reference a Hot in Start or Run fuse but I've yet to find it, it's not in the fuse box inside the cab and as far as I know there's no other fuse box?

Things I've done are:
Replaced Fuel Pump Cut Off Relay
Jumped the Oil Pressure Safety Switch
Verified that the fuel pump does work by using the wire off of the I terminal that has the fuel ump run during cranking
Checked wiring around carb due to a fire in that area

 

The main wire from the large hot terminal on the starter solenoid, that runs through the inertia switch, should be hot at the fuel pump relay all the time. If you don't have power at the fuel pump relay from the starter solenoid something is wrong with that circuit.

Now undo the jumper at the oil pressure switch and test for power in one of the two leads with the key on. If you don't have power at the oil pressure switch with the key on, jumping it isn't going to help. You need power! The diagram you posted suggests fuse #18 which is a 15 amp fuse. See if youf fuse block has a number 18 and check all your 15 amp fuses. If you've got power and you jump it, you should have power from this circuit at the fuel pump relay.

Once you've established you've got power getting to the fuel pump relay from both the large hot lug on the starter solenoid (through the fusible link and inertia switch) and also through the oil pressure switch side you can check and see if you're getting power to the fuel tank selector relay (which I have heard can be confused with the fuel pump relay). Also make sure the ground wire for the relays is making good ground. If the ground wire isn't grounding, having power won't help.

About all you can do is keep tracing the power though all the switches until it's all the way back to the pump(s).

 

While the diagram you posted is probably fine, Ford's diagrams and troubleshooting guides are here on my site: Fuel Senders & Pumps - ???Gary's Garagemahal. The pages under #19 cover your fuel system, but if you want to follow the wires to find where hot at all times our hot in start and run circuits come from you will want the other links.

 

Thank you for the help. I checked the OPS switch and it only has 12 volts with the key in the run position. The main wire running through the inertia switch always has 12 volts as well. I do know the tank selector valve is dead and the truck needs a new one, but it's been dead for a while now and has been running fine. I've checked all the fuses as well and none are blown and there is no #18 fuse spot that's used.

 

Found the problem. After checking all the voltages and tracing wires I finally pulled the inertia switch and placed a jumper wire between the two terminals instead of just resetting it. Now the fuel pump turns on like it should.

 

Glad you found it.

 

Thank you for your site Gary! That'll help me and others in the long run with part numbers.

 

Welcome! Glad it helps. But let me know if you find a problem or realize something you need is missing. Or, for that matter, have a suggestion to make it better.

 

Once it was running I was sorting out vacuum leaks, found out I had the wrong manifold to EGR plate gasket so I went and bought a new one. Now the truck won't stay running and make a noise that reminds me of children screaming after installing the correct gasket. I do have the EGR blocked off, so I'm wondering if maybe I need to plug the EGR hole? Sorry for asking basic questions. My background is in fuel injection on Toyota's. Carbs are something I'm trying to learn. Along with the rest of the 460 information.

 

Bottom to top.

- intake manifold.
- thin hi temperature gasket.
- heavy cast iron EGR plate.
- thick 1/4" or more fiber insulating gasket / spacer.
- carburetor.

Sounds like you've got a whistling vacuum leak and you'll have to try again, this time making absolutely sure the intake is perfectly clean (there is probably a little chunk of the old thin hi temp intake to spacer gasket stuck on the intake causing a leak) and you might also spend some time block sanding the cast iron EGR spacer to make sure that it's perfectly flat and clean. Also set the carb on something flat and check to make sure the base has not been warped out of shape from over-torquing.

Beyond that, maybe you forgot to hook a vacuum line up after re-installing the carb?

Also, why block or disable the EGR? As far as I'm concerned a properly functioning EGR improves gas mileage and engine cooling. It only opens under high vacuum (light throttle) cruise conditions. Otherwise it's not a factor under full throttle, so there's no gains to be realized from disabling it.

If that doesn't help, start a new thread for this new issue so others will see it and chime in.