Fuel Inertia Switch ?

The only things on the S Series (and most other GMs as well) are. The fuel pump, The FP relay, The ECM and the Oil pressure switch that also controls the fuel pump. The ECM triggers the pump for 2-3 seconds to pressurize the system. Then once the engine starts and generates oil pressure the OP switch closes and the pump runs. IF oil pressure drops below about 10 PSI, it shuts down the fuel pump. If you hear the pump run those 2-3 seconds when you turn the key on, the ECM signal is there and the pump is working. If not check the fuse and the pump. If the engine will start and run a couple seconds and then shuts down check the oil pump switch circuit and the switch. Without it working the pump will not run and keep fuel pressure up.

The relay isn't turning the pump on, I have only 1 hot terminal,where the relay plugs in.It has 4 prongs on it ,I'm not getting but the 1

12volts when the switch is off or on.Ian says when the switch is on,I should have voltage on 2 prongs.I replaced the oil switch the oil pressure gauge works fine.I have the relay out and a wire run from the there to the fuse box ign. on to make the pump run.Hope this makes sense.Anyway I would like to fix it right.Any suggestions on where else I should look further,would be greatly appreciate!Thanks Bobby

Steve I went back and read your post,now I'm thinking it must be in the ECM,not sending current to the relay,because I have a oil pressure guage and it shoots the oil pressure to 70 psi.and wont fire at all until I bypass the relay.Thanks Again bobby

Steve W is correct in the fact that the fuel pump can be turned on by oil pressure but oil pressure is only used in case of Fuel Pump Relay failure. If all wiring is in good condition and fuel pump is ok but the relay has failed then after a predetermined amount of oil pressure is obtained the fuel pump will turn on . If the relay is ok and all wiring is ok then the loss of oil pressure WILL NOT shut off the fuel pump. Be sure to check the grounds real good. BTW the ECM works mostly on grounds , very seldom does the ECM actually provide power to something mostly it will provide a ground to relay that will provide the power for the device

The oil pressure switch is NOT the same sender that controls the gauge.

If the engine will start and run a couple

This is not correct.

Ian