hi i recently got a 1992 f150 4x4 4.9 liter pickup with dual tanks . ive read thur the post here and i havent seen anyone with same problem i have ... truck cranks runs great on front tank ,, will not run on back tank but you can start it on front tank and change it to back and it will run but lacks horsepower ... i can say it does not pump fuel from front to back or anything like that ...would this be a fuel filter problem ? thanks for any help

 

I have the exact same problem with a 1994 f150 5 liter. I put a new fuel filter on but it made no difference. If the engine is warmed up it will start on the back tank but if its sat for more than a couple of hours I have to start it on the front tank.
When I drive on the front tank I have all the power that I need, but on the back tank it's starved, if I come to a hill I will loose speed even if I floor it.
When I step on the gas it does very little, so whenever I go to pass someone I have to switch to the front tank.

Any ideas?

Thanks.

 

Your rear pump is weak, and when you switch to it while running the tank selector valve does not flip all the way from a lack of rear tank pressure, so the engine is still feeding off the front tank.

Adrianspeeder

 

On a 92 doesn't he have the twin in-tank high pressure pumps with no selector valve?

Possibly the rear pump is going out, also possible that the "sock" (i.e. the suction filter) on the rear pump is partially clogged. No way to check that out without pulling the pump

 

Weak rear pump, or blockage inside the tank. The external filter is shared by all the tanks, and switching occurs inside the FDM (pump). Many pickup owners say it's easier to lift the bed than to drop the tank.

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