When I fill my tank, sometimes I get a full reading on the guage, sometimes I don't. Even when I get a full reading, it mis-reads after the car is shut off and res-started.

Is this typically a bad sending unit in the gas tank ? How hard is it to install a new sender ?

 

It definitely sounds like a bad sending unit, but I suppose it could be the gauge itself. Change the sending unit would be a pain in the butt. The whole gas tank has to come out. I've never done it, but I've read the threads of others who have. It's not a task for the faint-hearted.

 

On coupes, the sender is easily accessed from the rear of the tank after removing the trunk card panel. However, on Convertibles, the sender is part of the Fuel Pump assembly and, as Sam said, requires removal of the Tank for access.