What noises are supposed to be made by each fuel pump in a 1984 240? When I turn my key to the 'on' position, neither fuel pump makes any noise--but the main pump seems to be working when the engine is running. However, the main pump makes a buzzing/hissing noise when the RPMs come down after revving the engine. I just replaced the prepump with a used one because I thought it was responsible for my car "cutting out" while driving, but that problem still remains and I'm wondering if I got a bad replacement pump (also my gas gauge no longer works, which also makes me suspect of the prepump). Any help would be greatly appreciated!

 

If the system retains its pressure you probably would not hear anything at that time as they do not need to pump fuel into a full system. The main pump can be heard quite clearly when the engine is running if you listen closely. The in-tank pump is harder to hear.

When you put the replacement pump in the tank did you change the sock filter? The fuel gauge sender will not affect the working of the tank pump as they are two separate units albeit on the same fitting. In fact you could transfer the pump part from the replacement tothe original to get your gauge working.