I just purchased a 87 F250 4x4 with a 460 and dual fuel tanks and it was not getting fuel to the carb but it runs if I pour gas into the carb. I figured it was an easy fix as it has a mechanical fuel pump on the front of the motor. I replaced it last night and still no fuel. I have around 10 gallons in the front tank and at least 5 in the rear. It does not matter which tank I flip the switch to, still no fuel. I have searched the threads but no luck. Also the gas gauge is pegged at full on either tank but I have read how to possible repair that. Could the problem be the selector tank fuel valve?
Thanks for any help.

 

Can you hear the Fuel Tank Selector Valve operating when you switch between Front and Rear?

 

No, I did not hear anything, I was wondering if I should.

 

So you didn't disconnect the line coming out of the pump and crank the engine to check for fuel before replacing the pump? If you want to throw away money I can give you an address to send it to.

Since both tanks are pegged at 'FULL' that is where I would start. Did it sit for a while? Most likely both the pumps and sending units are bad. Check for power at the tanks.

 

Well, if you’re close to it, I would think you would hear it switching. You should hear it switch when moving selector from Rear to Front switch position.

Food for thought;

Check fuse #15, 10 amp, this supplies power to the Fuel Selector Switch.

Clogged Fuel Filter?
Blockage/crimp in Fuel lines?

Does your Instrument Cluster have a Tachometer?
Dually?

Also, like he said, if you haven’t, check the fuel output from the Fuel Pump at the carburetor.

What model carburetor do you have?

 

Do carbed trucks have in tank pumps?
Personally, I would not throw a pump at something just hoping for a fix. That's not the best way to trouble shoot. First thing I check is that there is gas getting to the mechanical pump. Easily done with a hand held vacuum pump and the little catch jar. If you plan to work on your own stuff, you should own one of these inexpensive tools. Then if there isn't good flow to the pump, start your way back through the switching valve and on to the tanks.

 

Definitely didn't hear anything. I did check fuses #15 & #18, they were ok. Have not checked the fusible links. Inertia switch was a thought I had last night but haven't checked that yet. I have yet to find a wiring diagram that doesn't show the circuit with only the mechanical fuel pump, only the in tank pumps.

I may be missing something but I sure have not seen a fuel filter, and no kinked lines.


Someone has replaced the original carb with a Holley double pumper with vacuum secondary and electric choke. They cut the metal fuel line coming out of the mechanical fuel pump about a foot up from the fuel pump and added about 18" of rubber line to the carb. I definitely removed the line from the carb to see if any fuel was coming out of that line while cranking the motor.


When I removed the supply line from the old fuel pump very little fuel came out of the line but since I am new to dual tanks I wasn't sure how much I would see come out with that fuel tank selector valve inline.

I do not have a tachometer and it's not a dually.

 

Ya, you're right, I shouldn't have just thrown an pump at it to see if that fixed it. That was just my first thought when no fuel, at least it was only $25.


So where do I put this hand held vacuum pump and what is the process?

 

When did I say anything about throwing parts at it hoping for a fix? Both tanks will have their own sending units. I suggested starting diagnostics at the tanks.

 

Ok, so you definitely don't have pumps in your tanks?

I think I have a Wiring Diagram for no pumps in tanks. Does not show an Inertia Switch, Relay or fuseable links.

Just Fuse 15, Selector Switch, Selector Valve, and the 2 sending units. I'll scan that in tomorrow and post it.

 

Updating schematic file.
1987

 

Ok, thanks. I can't imagine it would have in-tank fuel pumps with a mechanical pump, and I got to thinking it probably wouldn't have an inertia switch, I think that wasn't added/needed unless it had electric fuel pumps.


I just checked wiring going to each tank and there are only 2 wires to each - front tank looks like blue and black and rear tank looks like yellow and black.

 

Yeah, so you can check the voltage to the sending unit selected by the switch.

Check continuity on the ground wires, they are notorious..

I wonder if the valve can be stuck in the middle, blocking fuel flow.... If you don't hear it switch, give it a kick....

 

I don't think you did and I was addressing the op with what I PERSONALLY do, which is nothing but my personal experience in trouble shooting. Sometimes a new part is the easiest way to diagnose, but generally there is a better way.
To the OP, the hand held vacuum pump kit comes with a little bottle. Hook the vacuum pump to the fitting that has the short tube in the jar and hook the fitting with the long tube to the fuel line from the tank. When you pump the vacuum pump you should see good return in the jar with little or no bubbles. Bubbles would indicated a bad hose or leak somewhere and very often this is misdiagnosed as a bad fuel pump. No return at all would indicate a blockage somewhere from the tank so you could do the same test under the truck on the tank side of the switching valve. While uncommon, I have seen the cam for the fuel pump come loose or be worn out. You can check that by trying to run the engine on a small jug of gas with a hose from the jug to the inlet side of the fuel pump.
Also, not sure on the 87, but on earlier trucks the main tank is the default tank and the one you will be on if you loose power to the switching valve.

 

1987