Wiring Electric Fuel Pump to Oil Pressure Switch

[jahmes143]

If an electric fuel pump loses power while the engine is running, isn’t the injection pump generally capable of continuing the fuel supply even without a fuel pump?

The reason I ask is that I always hear people saying to wire the electric fuel pump to an oil pressure switch so that if oil pressure drops, fuel flow also stops. Generally there are two reasons for this fail-safe: 1) cuts fuel in case of a crash (so fuel doesn’t flow everywhere); and 2) in the event of engine failure (e.g. extreme loss of oil) the fuel supply is cut to prevent running the engine without oil and ruining the engine.

If the IP is capable of powering the engine even without the fuel pump running, reason #2 doesn’t seem to hold water. Am I missing something?

 

[Twiztedmods]

That's usually the case for gas engines, not the diesel. Like you said the IP is more then capable of running the engine without the external pump, as far as I know the external pump is more or less for priming the IP.

 

[K85 Octane]

I would wire the oil pressure switch to a light or better yet, a buzzer.
I wouldn't want the engine shutting off at the wrong time. I'd rather hear a buzzer and then shut the engine off, just in case I'm in mid turn or something.

 

[jahmes143]

Great idea. I think I'll do that.

 

[Russell]

The oil pressure switch is not a permissive to an engine running. Never has been. It is wired in parallel with the fuel pump relay. If the fuel pump relay fails, as they often do, it will continue to run the pump via the oil pressure switch. The switch changes at 5psi rising btw

 

[jahmes143]

Russ - I'm no wiring expert, but I think sometimes the oil pressure switch IS a permissive to engine running, particularly in the racing context, at least for gasoline engines. It's as follows: fuel pump (and engine) will ONLY run IF starter is engaged OR there is oil pressure. Check out the wiring configuration in this article, for example. http://www.how-to-build-hotrods.com/electric-fuel-pump.html. Is this not a permissive?

 

[Russell]

Speaking in the context of a stock GM vehicle*

Of course you can wire one up to behave as a permissive if you want but I don't see the point. If you are upside down your vehicle won't stay running for long. Your fuel system will suck up air and the engine will die. When it stops the ECM stops the fuel pump.

Seems like a good way to add a failure point that can strand you. The likelyhood of it saving you in a rollover is slim as the fuel will pour out your tanks just fine without the pump and even if you do have an engine fire the wiring for the pump will be shorted out in a real hurry.