I recently had the fuel filter changed on my 96' Ford F-150 pickup with
5.0L engine with dual fuel tanks. Since that time, no matter what position
the fuel selector switch is in, return fuel only goes into the front tank.
I had a F150 with the exact same problem. On mine, there was a large plastic
valve that switched the tanks. It's powered by the fuel pumps. If the pump
in the front tank is on, the valve moves to select that tank. Same for the
rear tank. Mine was stuck half way between the two positions.
Ford used to use a switching valve but it was long gone by 96. On these
trucks everything is done by the pumps. When a pump turns on that same pump
should open a valve allowing the return to flow back into that same tank,
while the valve on the other pump closes, blocking return to that tank. What
usually happens is that the pump which is turned off has a defective return
valve which does not close and allows the returned fuel to overflow that
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