First off this is my first post, I bought this truck yesterday and have already learned so much. I have owned 3 F150's in the past but this is my first F250

I have a 92 F-250 with a 351 engine, auto tranny, and 4x4 with dual tanks. The front tank sending unit to the fuel gauge is bad, I was told that when I bought it. It was full of gas though as the guy I bought it from just filled it on the way to meet me. The back tank was on 1/4 so just to be safe I filled it and ran off it since the gauge for the rear tank worked.

As I got to cleaning and checking everything out today I noticed gas dripping around the gas cap and down the inside of the bed and on the ground. I tried to replace the O-ring with no luck, changed the gas cap, and no luck.

Sooooo I switch the tank selector switch in the cab to the front tank and it almost instantly stopped dripping. It was weird because when you take the cap off the gas was clear up to the edge of the filler tube and running over until I switched to the front tank.

I see in the FAQ section there is mention of a "fuel tank selector valve" going bad and causing some issues but none like this. Is is possible the valve is pumping gas out of the back tank into the front one and overfilling it when the switch is set on the rear tank?

 

I apologize guys and gals, as I continued to search the forum I found a few different people that had similar problems and it all ended with that darn valve, guess I will look into getting one soon.

 

92? You don't have a "fuel tank selector valve", just gotta a switch on the dash and a FMU in each tank.

The check valve in supply line that is a part of the FMU in the front tank is leaking, allowing the fuel from the rear tank to be pumped into it.

Change the front FMU to correct the problem, you can look over the fuel level sender at that point, see if it needs replaced or has an easily correctable issue of some sort.

 

What is the FMU? sorry im new to these fuel problems lol I have a new car that doesnt have any issues and now I take on an older truck to see if I can spend as much money on it as I do my car lol.

 

Oh sorry, FMU = "Fuel management unit".

 

So I went to autozone and oreilly and they say I have a fuel selector valve? I'm confused, where do I look to find which I have?

 

Here is one description that might help. Ford F250 Dual Fuel Tank Problem

The following is from the 1996 Factory Shop Manual. It is my understanding that the '92 to '96 were pretty much the same. It wouldn't paste the pics (have to work on that.) Replacing your pump should fix this.
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Fuel Pump
The electric fuel delivery system used on the 4.9L, 5.0L, 5.8L and 7.5L multiport fuel injection (MFI) engines (6007) consists of a fuel delivery module (FDM) and sending unit. The fuel delivery module includes a high-pressure fuel pump (9350), venturi jet pump, supply check valve, and a shuttle selector valve located internally to a reservoir mounted from the fuel tank sender flange.

The following provides a brief description and function of each of the fuel delivery module internal components.

The high-pressure fuel pump is located inside the module.

The shuttle selector valve opens the return tube to the tank and the return flow is directed to the appropriate tank on vehicles equipped with dual tanks.

The supply check valve, which is normally closed, opens when the outlet pressure from the energized pump exceeds the opposing check valve spring force. When the fuel pump is de-energized (i.e., engine is shut off), the supply check valve closes to maintain pump prime and fuel supply tube pressure.

A portion of the high-pressure flow from the fuel pump is diverted to operate the venturi jet pump. The venturi-type fuel pump draws fuel from the fuel tank (9002) into the fuel delivery module reservoir to augment the engine return flow. This process ensures an adequate fuel supply to the fuel pump during extreme vehicle maneuvers and steep vehicle altitudes with low-tank fill levels.

The inlet of the venturi pump has a nylon filter on it to prevent dirt and other particulate matter from entering the system. Water in the fuel tank can pass through the filter without restriction.

The in-tank mounted fuel delivery module containing the fuel pump is capable of supplying 105 liters (27.7 gallons) of fuel per hour at a working pressure of 270.0 kPa (39 psi) for the 5.0L, 5.8L and 7.5L MFI engines. The fuel delivery module can supply 90 liters (23.7 gallons) per hour at 380 kPa (55 psi) for the 4.9L SFI engine. The fuel pump has an internal pressure relief valve to provide over-pressure protection in the event the fuel flow becomes restricted. Over-pressure is restricted to 850 kPa (123 psi) and reduced fuel flow will result. The system pressure is controlled by a fuel pressure regulator (9C968) on the engine.

 

Hey thanks that actually helps alot, I'll try to pick up the parts to get it fixed this week.

Oh and one more question, if I buy the fuel pump part thaf dits in the tank with the bad valves in it and not the whole assembly that it mounts to will that also fix my fuel gauge?

 

Maybe and maybe not. It could be the sending unit and it could be the wiring harness. I am having the same problem with my gauge on the front. On mine, I am going to check my sending unit when I change the pump. When you pull yours out check the ohms with the float in the full position and the empty position. It should be 145 ohms while in the full position and 22.5 ohms in the empty position. If it is within specs your problem is the wiring harness. If it is not within specs it is the sending unit.

I say test first to avoid buying parts that are not needed.

 

No it would not help the gauge issue.
The sender is a different part mounted on the same tubing.

The part with the valves and pump:




The sending unit for the gauge:


The whole unit:


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