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evo rider
08-14-2008, 19:48
Is there any reason why a 6.5 turbo would run with the fuel pump wires being disconnected because my uncles truck is experiencing that :confused:

Thanks
DmaxMaverick
08-14-2008, 20:27
That means the fuel system and IP is healthy. The IP has a transfer pump, and it will draw fuel if it's primed. It's additional strain on the pump, so I don't suggest you let it continue now you know about it (fix the LP).
evo rider
08-19-2008, 19:18
so we replaced the fuel pump relay but it still fails to get power to the pump unless power is jumped at the relay. The pump is supposed to have power at all times after startup right?. Our fuel pump only has power to it while the motor is cranked but once it starts the power shuts off....:confused:
a5150nut
08-19-2008, 20:34
At the rear of the vally, behind the glow plug relay is the oil pressure switch. It's a fail safe if the engine quits it shuts off the fuel pump. When they go bad, no power to the pump after cranking.
GMC Hauler
08-20-2008, 16:22
At the rear of the vally, behind the glow plug relay is the oil pressure switch. It's a fail safe if the engine quits it shuts off the fuel pump. When they go bad, no power to the pump after cranking.

He has the fuel pump relay, which is in parallel with the OPS. If the OPS quits while the engine is running, it has no effect, because the fuel pump relay still powers the lift pump.
DmaxMaverick
08-20-2008, 17:20
He has the fuel pump relay, which is in parallel with the OPS. If the OPS quits while the engine is running, it has no effect, because the fuel pump relay still powers the lift pump.
The purpose is not to keep the pump running, but to shut it off if the engine stops with the key on, like after a collision. Earlier models only had the relay for key-on cycles. The OPS, once the engine is running, is the only source of power for the lift pump.
GMC Hauler
08-21-2008, 05:00
The purpose is not to keep the pump running, but to shut it off if the engine stops with the key on, like after a collision. Earlier models only had the relay for key-on cycles. The OPS, once the engine is running, is the only source of power for the lift pump.

Check this attachment. This comes from GM's material, not mine. This is why Kennedy's fuel pump wiring harness is not necessary on 96 and newer.
evo rider
08-25-2008, 10:53
Thanks for the diagram. That was very helpful. It was the OPS that was giving us trouble. Now she runs like a champ