Here's one for ya: 1988 Ford F150 4x4 XLT Lariat. 302 C6 with dual tanks. The front tank runs just fine. The rear tank will make the engine sputter and spit only when trying to accelerate. When I was on the highway today, I switched to the rear tank, and it ran fine for almost an hour. Accelerating after the off-ramp? Sputter. Now, why would it run just fine at a consistent speed (70 mph), but not on take off? Also, the fuel gauge works perfect with the front tank, but gets pegged past "full" on the rear tank. And, lastly, after my trip with it today, which started with two full tanks, the front tank had lost about a quarter of a tank, despite only running the truck down the on ramp and up to speed. The rear tank did the rest of the driving.

Could this be BOTH rear fuel pump, sending unit, plus the selector valve? The tanks have never seemed to swap gas before, like in the classic selector valve malfunction. I have no idea how much gas is in the rear tank right now, as I didn't fill it up, and that gauge just stays pegged.

Your thoughts, gents...?

 

My guess is you have a bad rear in-tank fuel pump and never used fuel from the rear tank.
The selector valve is set to the front tank and stays there with the bad rear pump.
The fuel gauge is reading right on the rear tank as it is full and being used.