How do you test the fuel tank sending unit on a 1995 jaguar xjs 4.0?

Answer 1

Apart from the obvious - run it very low on fuel and check the gauge reading, fill it up and check again - you need to remove the sender from the tank. Access it by taking out spare wheel and carpet curtain at the back of the boot. It's a round white device about 3 inches dia with three wires attached. Make a note of which colour wire goes where. With tank no more than a third full (you don't have to drain it) knock or twist round the metal retainer with three tabs. We use a pair of long noses pliers to engage two of the three tabs. Twist anti-clock about 30 degrees so that the ring can be pulled out. Remove the sender unit which has a long thin steel arm with a float on the end. You may need to wiggle it a bit. You can then connect a digital voltmeter to two of the pins and see that the resistance changes smoothly as you move the float arm up and down. It's a very common failure so in practice it's best just to fit a new one.