Its a bad ground, but its easy to fix. By the fuse block/hood open latch (in side the car) there is a bundle of wire, find the light blue wire, cut it and connect each end to the car body. I did mine and it works. But quarter tank is now empty, rpm guage is fine... Hey check out www.lincolnsonline.com and go to the tech part, and see "dash ground fix" that's how i learned this very helpfull tip.
Look for a bad grounding wire. If the fule gauge sending unti is properly gounded, it should send the signal to the fuel gauge, make sure the fuel gauge is grounded. You may have a bad fuel gauge.
most failures lead to the fuel sending unit inside fuel tank.and yes the tank must come out
The main advantages of using a marking gauge over a pencil and ruler is that you can repeat the settings on every workpiece that you mark out. (i.e. you can make an identical mark on each of the pieces you are working with).
Fuel tank sending unit. Fuse.
The fuel level sensor is shorted or a wire is shorted.
In most cases it is the sending unit in the fuel tank that is faulty. Disconnect the wire at the fuel tank and ground that wire, turn the key on and see if the fuel gauge goes to the full mark. If it does the sending unit has failed. The float is also known to fail and sink to the bottom.
car may turn over but not start; fuel gauge might be off; car will run ragged with little power
Typically when a fuel gauge reads incorrectly it is the fuel sending unit in the fuel tank.In order to determine where the problem really is accessing the fuel sending unit on newer cars is fairly easy.Most have a access area either from removing the bottom of the back seat or from the trunk area under the carpet.In short if the fuel sending signal wire is grounded it should make the gauge either go back to empty or to the full mark IF it is not working properly.Just a simple check to verify if the part above is defective,or possibly your gauge itself has a electrical issue.I just recently fixed a exact issue as I have done before gauge read full and already knew the problem.
If you really want to fix it, then you will have to drop the fuel tank and remove the sensor, go from there. You can check the float while it is your hand, just plug the wire harness in, move it up and down and have someone check the gauge. Might also be the gauge needle in the dash. You will find out this way.