Mine did the same thing then stopped working alltogether.
It could be the sender but I suspect a bad ground from the sender to the car. If I put a resistor between the wire to the sender and the frame, I got a reading on the gage. I have not determined if the bad ground is between the sender and the mounting flange or the flange and the tank.
Bob Shaw


87 Raizer, 4.3V6, Mod TH700R4,231CHD, detroit rear and LSD front, bouncy seats, 2" lift and 32x15 BFG MT tires.