2001 Ford Explorer Sport Been Dying Randomly Starting Will Turnover Fire

I have a 2001 ford explorer sport. it has been dying randomly and not starting. it will turnover but not fire up.today my dad sprayed starter fluid into the intake and it started again and the fuel pump can be heard running only when the truck is running not when the key is turned on. I wanted to know what i need to check in the system so that if I replace the fuel pump itself and it still doesnt work i know what else to replace