I have a holley electric fuel pump on my cj7, it is wired to a switched 12v source and runs continusously while the key is on. I don't think this is right, what kind of switch can I get and where do I wire it in?
btw, it has a holley avenger truck carb - 4 bbl if that matters
Yep. Different system with the fuel pump controlled by the engine computer on a fuel injected application. They pressurize the rail first by running for 2-4 seconds then shut down. When the key is moved to Start, they pump runs from that point till when the key is moved to Off. On some vehicles there is an interlock with oil pressure. As long as there is oil pressure the fuel pump relay gets power. There are also impact/rollover switches.
You could put in a cutoff switch or safety interlock like race cars use. Just a simple safety switch that cuts power to the pump. Better to use a relay for that type of application though.
You can wire it with a relay through the oil pressure safety switch on the oil sender with a bypass from the solenoid so it runs when the starter is turning. Pretty much the same as you wire in a coil.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Good to know. I put a 3.4L in my Cherokee some time ago and it requires use of an electronic fuel pump. It's still carbureted however. So I'm not sure about using a pressure interlock. The jeep doesn't get used all that often and it seems the float eventually runs dry (it's been needing a rebuild for ages...). So the pump has to run a bit into order to refill the carb and start running. There wouldn't be any oil pressure yet.
That said, it's a little annoying to hear the pump rumble when the engine's off but in the run position. It'd be nice to either have a quieter pump or some sort of cut-off like you mention. Any idea about one suited for a carb setup? One with some sort of shut-off timer with a pressure sensor override would seem like the right idea.
Agreed, no sense running the full current of what a pump might draw through a switch. They tend to overheat. Granted a beefier switch would handle it better. It'd be a toss-up between spending more on the switch or the cost and the wiring up of a relay circuit.
The cutoff switch is commonly called an "Inertial Cut-Off Switch" and can be had from just about any auto vendor (or maby even NAPA). It's just an impact switch similar to an airbag sensor that cuts the power to your pump should it get whacked hard enough. And by hard, I mean enough to bend metal or set off the air bags, not bouncing on a trail. Fairly sure the new Jeeps have them.
A timer circuit would have to be made, not sure of any commercial sources. I could give some suggestions if your handy with electronics.
The Jeep engines have an oil pressure switch on the sender unit. This can be used for the pump on in the run position with a relay. Stock, the switch runs the manifold heater with a relay on the 258 and the choke.
For starting, you feed the pump power from the starter solenoid.
This way the pump runs direct with the starter and only with oil pressure when the key is in run.
You can put your safety cutoff on the relay circuit if you want one in easy enough. It would just need to cut the power.
The carb emptying out when it sits normally means you have the gas filter in upside down by the way. The filter has two outlets, the center one goes to the carb and the top one goes to the return line. If the return line isn't at the top the gas will syphon back to the tank when it sits. A pinhole leak in the suction side line from the pump can also let air in when sitting and only leave a small stain because it is on the suction side.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
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