Your fuel sending unit is not giving the correct reading to your gauge
Either the gauge is broken or the sender is broken.
fuel sending unit broken wire or gauge is bad
a bad sending unit in the gas tank.
On a car, there is a float inside your gas tank. It is attached to a switch that sends the empty.....full signals to your fuel gauge.
you should go to a car shop for that one!:)
check your ground wire to the gauge
The fuel gauge could be getting improper signals from the fuel sensor. The sensor is located inside of the fuel tank.
The floater inside your pump is sticking. You will have to replace your fuel pump in order to fix this problem.
You need a new fuel pump
In most cases the fuel gauge sending unit in the fuel tank has failed.
with a full tank of gas the gauge will drop to "E" then after a few seconds it will jump back to correct reading.
Most Likly a fuel sender problem