I have an 87 Z-28, 305 TPI. fuel pump wasn't working so I replaced it. it ran ok for a couple hours then the pump sounded bad so I replaced it again with an ac delco pump. the new pump sounds ok but it wouldn't stay running and my fuel pressure was only up to 15 lbs. I changed the fuel pump relay, fuel pressure regulator and fuel filter. after changing the regulator a while ago the pressure goes up to 10 lbs. while the pump energizes then drops to zero when the pump stops energizing. I checked for any fuel leaks and can't find any. is there something I overlooked? what's going on with my car? any help will be greatly appreciated. thanks

 

Might try squeezing the rubber fuel return line with a set of smooth jawed pliers. If pressure rises, the regulator is leaking internally. If there was some debris in the fuel system, it could wind up being lodged in the fuel press reg. If some debris remained in the system after reg replacement, it could cause the same issue with the new regulator.

Injector leaking could also explain the low pressure, but it would have to be leaking pretty bad. Could try capping the cold start inj line port on the fuel rail to isolate the cold start inj.

Also, make sure the AC Delco pump is for a TPI and not a TBI system.

 

might have a little air in your system. same thing happens to me every time i pull my fuel rail. try turning you key on so you hear the pump, then turn it off after the pump stops. after about 5 sec, turn it on again so the pump kicks in. do this about 10-12 times. it should be more than enough to fill your rail and get up to your injectors.