1998 Chevy Blazer Fuel system

My truck won't start. The fuel pump has been replaced twice before. I can hear the fuel pump when I put the truck in the run position. I also took the fuel line off the fuel filter to see if fuel was going through the filter and it is. I haven't ruled anything out but I don't think it's the filter or the pump. I put gas in the throttle body and it fires up untill that fuel runs out