I bought a 95 Z that didn't run(engine locked up). I now have the new enigine in it and running but when you turn the key on, the fuel gauge goes all the way past the F. The car only has about 6 gallons in it right now. I don't know if it did it when I bought it since it didn't run, I didn't check it. The car sat for a long time before I bought it and the gas that was in it was garbage. I drained the tank and cleaned everything out of it so I don't think it is a problem with the sending unit. We unplugged the pump harness from the body by the rear end and the gauge still does it. It acts like the sending unit wire is grounded out somewhere but I can't figure out where. I have the dash and interior trim along the sills all apart but I don't see a problem. Are these cars prone for fuel guage problems? The dealer says you can't replace just the gauge so should I send the cluster out to someone or what should I do???? PLEASE HELP, I'm going nuts!! This car is gonna be for my wife so I have to get that gauge working. Thanks.

 

I have a similar problem with my car after a fuel pump replacement i did recently. Most likely its reading full due to damage to the float/sending unit in the tank. I doubt its a problem with the actual guage since it goes up and reads past full. What you should do is pull the fuel pump assembly and put a multimeter on the sending wire (purple i think) and check the ohms as you move the float up and down to see that its functioning. I think 0=empty and somthing like 99=full. Maybe your float is jammed in the full position. I kind of forced mine back in so thats probably whats wrong with it. Its kind of a PITA to get the assembly back in right with that plastic housing inside the tank.
Check this out too...link