Just got a 1997 Blazer. The old owner just recently installed new fuel pump & since then the gas gauge doesnt work. When the key is off the gauge reads 1/4 of a tank but when I turn the key on the gauge drops to empty. Any ideas on what to look for in the problem.

 

since the fuel pump is new that means the sending unit is brand new also since they are built into the fuel pump. Assuming that the fuel pump was replaced was the original fuel pump when you install a new one the 4 pin connector at the pump has to be cut out and the newer style has to be spliced in, maybe the fuel gauge signal wire splice came apart.