fuel pump

Fuel pump quit.Got a used one(free) put it in and now it starves for fuel until thing with three wire connector and A B + - markings near throttle body air horn/intake is unplugged.With that unplugged the car runs good while accelerating but pulses on decelleration.Have heard that used fuel pumps are seldom good to re-install after they have been sitting around for any length of time.Do all GM have same pump pressure?

Different model engines as well as differnt years run on different fuel pressures. Pressure can be anywhere from 15psi to 65 psi.