I bought a 1990 F-150 (Gasoline powered 351) that I have been repairing. (If the person who owned this before I bought it had done the things to an animal what he did to this truck, he would be in prison for animal abuse but that's another story). I just about had it ready when I made the mistake of hitting the fuel selector switch. It had only been running on the front tank. Now it won't run at all even after trying to swap back to the front tank. I pulled the switch and it appears to be fine as it passes the ohm meter continuity test. I put a jumper across the fuel pump and 12VDC wire at the back of the switch and each pump operates when jumpered to the individual pump. However, the rear tank was empty so I don't know if the pump would have been strong enough to allow the engine to run. However, when I run the front pump with the jumper, the fuel pours into the back tank. I pulled the rear tank because I was told that I might have a fuel selector valve around the rear tank (That's how I found out about the fuel now dumping to the rear tank when the front pump runs). However, I couldn't find it and I can't find one on the frame rail as most of these forums were indicating that the selector valve would be located. Nor could I find a selector valve for a 1990 gas powered F-150 on the wiring diagram though there is a selector valve for the 1990 F-150 diesel powered truck. My system consists of high pressure in tank pumps and no external pump. My questions are:

1) Does this model have a selector valve or is this totally handled by the FDM ? If it has a selector valve, where is it located ?
2) Why doesn't either pump run when the switch is switched when it appears that the switch is good and both pumps will run with 12VDC applied to them ? Would disconnecting the battery reset this to operate the switch properly again ?
3) Will changing the rear pump solve this problem ? If so, are F-150 dual tank pumps different than say a Mustang pump (I have an extra Mustang pump I can try) ?
4) If the FDM is bad, can it be repaired or is it a replacement part only ?

Thanks for the help. I want to get this thing fixed so I can sell it.

 

1) FDM.
2) Probably the stuck rear shuttle valve, but there are other possibilities, like the inertia switch.
3) Probably not. The actual pump motor might interchange, but you'd have to install it in the truck FDM.
4) The pump & sender can be replaced; if the shuttle valve or venturi are damaged, the FDM is ruined.

Read ALL these captions:



BTW
There's no such thing as a diesel F150 of any year in the US.

 

Thanks a lot for the help. You are right about the non-existent diesel F-150. I was going by the vehicle repair manual for a 1990 Ford truck and mis-ascribed the diesel as being used on F-150's. Anyway, I jumpered across the back of the fuel switch to operate each pump. So if it is a bad inertia switch, it shouldn't have worked with the jumper across it as the jumper merely replaced the switch function. So it does sound like the shutter valve is the problem. Can the shutter valve possibly be freed up by using say some fresh gasoline to flush it ? Is an FDM available at the parts store or is it a dealer only item ? Thanks again for the help. I have been used to the older tank system and wasn't sure what was going on with this system. It helps to have the input of someone who is experienced with this type of system.

 

It's "shuttle"; not "shutter". Read those captions. Yes, any parts supplier will sell you a FDM. But it sounds like your tank select switch has problems - if it doesn't work without a jumper, I think it's time for a new one. They're not expensive - IIRC, ~$30 at Parts+Plus, and probably less from RockAuto.