I would fill it up and it would show 3/4. Then drop fast from there. Put a new sending unit and new float now it is stuck on empty. Anybody have experience with this type of problem. Help!

 

I wonder of the float somehow became stuck on reassembly?

Also, some later XJSs had an 'anti slosh module'. I'm not familiar with the details but I think the module is in the fuel gauge circuit and I know others report problems with it from time to time. Might be worth some research?

Cheers
DD

 

Is the tank at all similar in the later XJS? There are a good deal of baffles in the older ones and I know that the float itself sits inside a shorter baffle that surrounds it. Easy to get it hung up, but you can put it in most of the way and check movement before securing.

Some sending units need adjustment to make sure they are in the proper range. 3/4 could need adjustment or it could be hung up.

There is data around somewhere if you search for the max and min resistance values.