I have a 2002 Pontiac Firebird V6 3.8L - The fuel gauge stopped working around October and I purchased a new sender for it. I had my mechanic install it, along with a racetronix fuel pump, and evap canister. The mechanic first told me that he had to do a lot of modification to get my pump to install...Both with my fuel lines and my fuel bucket... Is this normal? None the less - I used THIS fuel level sending unit... It didn't work.

Here's whats happening - and nothing has changed whatsoever either...

My gauge either reads EMPTY or FULL...no in between. When it reads empty, and even begins to descend down to empty, my check gauges lights come on... What could be the issue here?

Edit: P.S. The car has a blown headgasket and isn't running currently - I'm preparing to swap motors but I want to fix everything else too.

 

Did you check the resistance of the sending unit vs. tank level, to see if the sensor is working correctly? Shoebox has a good guide to fuel gauge problems on the earlier models. I suspect your newer model will be similar:

http://shbox.com/1/4th_gen_tech2.html#fuel_gauge