I've been reading, and reading, just replaced the front tank fdm as it was not working. Rear was working and sort'a fill'in the front tank also. After replacement, front tank got 6 gals & the rear got filled. Drove on the rear tank for 8 miles, gauge went down to 3/4's???? Switched back to the front and she was almost full. So the ck valve theory being bad in the front pump? Really don't want to drop it again after installing a new one. Any suggestions would really help.
Thanks,
Jeff

 

That's the sound of it. Sucks to re-do a job like that. What brand did you use?

I always prefer to slip the bed back to access the mid tank.

 

Bosch, should I go with the Ford oem one?

 

I would think Bosch would be a good one. Any brand can be defective. I usually pick Airtex & have never gotten a bad one. Ford/Motorcraft is preferred if your wallet is fat.

 

I had a 1993 f-150 4x4 351 in Wyoming and had the same problem but, it wasn't a check valve, it was the fuel tank selector valve. The inner diaphram had separated and it would return to the rear tank no matter which tank you selected in the cab. . . I filled it up one day and left it running in the dead of winter, while I was at the doctors office. I came out and it flooded the parking lot with gasoline. I took it to Ford and they replaced it that day. When I came to pick it up, the tech took the factory unit apart and showed the damaged components to me. Who knew?! . . . .

 

I was thinking they changed fuel system types in '92 and eliminated the "selector valve". ?

And I suppose I should correct my terminology to say a bad shuttle valve, instead of "check valve", thus allowing returning fuel from the engine to enter the wrong tank.

The following provides a brief description and function of each of the FDM internal components.

The high pressure fuel pump is located inside the module.

The shuttle selector valve opens the return line 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 pump is de-energized (i.e., engine is shut off), the supply check valve closes to maintain pump prime and fuel supply line pressure.

A portion of the high pressure flow from the pump is diverted to operate the venturi jet pump. The venturi pump draws fuel from the tank into the fuel delivery module reservoir to augment the engine return flow. This process ensures an adequate fuel supply to the pump during extreme vehicle maneuvers and steep vehicle attitudes 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.

 

Ford stopped using the dual function reservoir 3-pump/2 tank fuel system in 1989. The F-series gasoline trucks went to the 2 high-pressure in tank pump/ 2 tank system (minus the DFR) in 1990.