1995 E36 320i vert,fuel gauge was working fine,then I had a small leak from the pump seal so unplugged the wires....sorted the leak(just tightened it) and plugged the wires back in,it now still works but shows (no matter how much fuel I have in) 3/4 of a tank and only goes down to half a tank when I KNOW ive used loads more fuel....do I have to re-calibrate it or reset it please?