Electric Fuel pump shut off

[clarkedj]

My sons 1978 Fiat 124 Spider has an electric fuel pump that he and I put in a couple of months ago. This and the electronic ignition have greatly increased the reliability of the car. A friend and I were talking about some of the work my son and I had performed on the car over the last couple of months. He made a good point about the fuel pump which really did not occur to me. He asked where I had connected the emergency cutoff for the fuel pump should the engine stop running in an accident. My response was " huh, I did not really think about that." He suggested I take care of the situation before my kid burned up in the car. I thought I would ask for suggestions from you guys about how others have resolved this problem. The pump itself I bought from Auto Zone and it was top of the line from them. I wired it directly to the ignition hot wire so when the key is turn the pump starts.

Thanks

Ed Clark

[So Cal Mark]

you could get an inertia switch from a Ford and wire it inline to the pump, or you could use an oil pressure switch like GM to prevent the pump from running unless there is oil pressure

[mbouse]

dang good question Ed. though i have not done so myself yet, i am contemplating pulling the mechanical fuel pump in favor of a low pressure electric pump.

where'd you get your switched power from? did you add a switch, or are you going off the ignition switch? i was contemplating using the idle solenoid feed circuit, running a wire all the way back to the trunk from the engine bay. it is an ignition switch controlled wire, so the pump would not run when the engine was switched off. i also am giving thought to adding a relay controlled by the oil pressure sensor... but haven't figured that out quite yet.

the fuel injected boyz should know how those relays are wired...

i'll be interested in hearing from them. RON??

[manoa matt]

Check the 75/76 wiring diagram for how and what to wire an electrical pump too. Just buy a relay and connect it in as in the diagram. It should come on with the ignition on and shut off after a few seconds if the car is not started. It's wired into the oil pressure warning light so it will cut off with no oil pressure, or a wreck.

[clarkedj]

mbouse,

I came off the ignition switch and it works like a champ.

Ed

[clarkedj]

matt,

Why would the 75/76 wiring diagrams contain an entry for wiring in an electric fuel pump? I like the suggestion on the relay and wiring to the oil pressure gauge as you and Mark suggested. Any suggestion on the relay or just some standard capable of handling the load.

Thanks

Ed

[rlux4]

The FI on our cars has a dual relay, which is just what it sounds like, two relays in a single body. The first side has a constant supply of 12V, unswitched. A second wire from the switch closes the first relay and power goes to the second relay, which needs the signal from the air flow meter to close the circuit and send the signal to the fuel pump. The engine turning over is all it takes to open a flap attached to a potentiometer in the air flow meter to energize the fuel pump. If the engine stops running, the flap would close and open the circuit going to the fuel pump.
This wouldn't be practical with a carbureted car (no air flow meter) so using the oil pressure makes sense in this case.
Ron

[baltobernie]

The only down side to wiring to the oil pressure switch is that it usually takes a while for the starter to build oil pressure, then the fuel pump begins filling the bowl before the engine can start. If the car has been sitting for a few days, this places extra load on the starter and battery while everything comes up. The inertia switch is a more elegant solution.

If the car has been sitting for a while, I like to wait a few seconds in the "on" position before engaging the starter, giving the fuel pump time to replace evaporated fuel and allowing the coil to reach maximum charge. The engine lights up immediately.

[mdrburchette]

matt,

Why would the 75/76 wiring diagrams contain an entry for wiring in an electric fuel pump? I like the suggestion on the relay and wiring to the oil pressure gauge as you and Mark suggested. Any suggestion on the relay or just some standard capable of handling the load.

Thanks

Ed

Actually, 74-76 were carbed with electric fuel pumps. I don't know why they went back to mechanical.