D2 facelift model fuel guage problem.

Hi im having trouble with the fuel guage on my D2 2002 facelift model. When I fill up the tank the guage goes up showing full then down to empty then back up again and this repeats until I'm about 3/4 full then the guage settles down. I had a new pump fitted and it's done it ever since. Does it need setting up?
Thanks