there's a short in the wiring. the fuel gauge works by reading electrical resistance in a circuit. if you have a break or a short in one of the wires it will constantly give an improper value to the computer and thusly your fuel gauge will read the wrong way. Some cars fail at the empty mark, as that is a safe bet to assume you're always on E, and sometimes they fail to the middle, or at max value. I'm nearly certain you have a problem in the circuit between the mechanical gauge and the fuel sender in the tank.
Originally Posted by Los
^He's been drinking beer and destroying pumpkins with brake rotors and sledge hammers.
So, pretty much just doing man stuff.