OK so I just ran out of petrol and the guage whilst going down still said 8.3 gal!
It's not just constantly flashing 18.5 like it used to which is a big improvement but I'll have to find some reading from somewhere! Will reset the system before and after refill and see what happens...
Measure the resistance across the fuel sender terminals when it is empty and again when full .It was working fine when I had it out ,moving and changing freely .