Is this wierd or what? I just bought an '89 F150 Lariat XLT with dual fuel tanks. Gas hit $2.97/ gal last week so I filled both of 'em up and set the tank selector to the front tank. I drove over 100 miles and the needle didn't budge off "Full". I switched to the rear tank and it was down to about 1/4 tank on the gauge. Gas was still 2.97 so I refilled the rear tank. It took about 10 gallons.

With the selector switch set to "Rear" the rear gauge reads correctly and the EFI bypass relief valve returns fuel to the front tank as evidenced by fuel running over and out under the front filler cap.

With the selector set to "Front", it still runs on the rear tank pump but reads the front gauge. I do not get a fuel spill overflow out of the front tank with the selector set to "Front". I suspect the transfer valve and the selector switch are both faulty. I can not get it to run off the front tank pump at all.

Does anybody out there know whazzupwiddis???

Thanks,

Dave

 

Very typical on these trucks, have a read through this album, it should help:
http://www.supermotors.net/registry/2742/66025

 

I saw the repair instructions then found a new Dual Function Reservoir at a local Ford dealer for $150.00, bought it and will install shortly. I'll let you know the results.

Dave

 

I have a 93 and it was similar. Only backwards. Ran off the front tank, back ddnt work. I finally got it switched to rear(fuel sending unit is out on front tank, constantly read empty) n now whn i switch it to the front i feel a buzzing in the floorboard driverside. I was told the valve jammed to the back but i lucked out cuz FSU wrks n reads gas level correctly. Only problem is it pressurizes front tank n throws gas out. Is there any way i can bypass the front tank all together?? And if i cant, how hard n long would it take to replace the FSU??

 

Your '93 fuel system is entirely different from the '89 that this thread is about. Read these captions:

 

I installed the new fuel transfer valve on the '89 and the trouble went away.... The installation was a piece of cake except for the raw gas drizzling down to my elbows....