I just picked up a 01 Xtreme blazer that was factory 4.3 but a previous owner pulled the 4.3 and installed a 305 in it. It has been setup like this for years and running and driving. Recently it stopped running. When you turn the switch on it prime's every time you turn the switch on. After you start it the pump stops pumping so it will only run for a minute or two. I can take the fuel pump relay out and use a jumper wire to jump the prongs and the pump will come on and it will start up and run. So I don't know if it's the relay or something else in the system not telling the factory pump to run.