Inertia Switch or Oil Pressure Loss Shut Off Switch to Fuel Pump

[Ol'Blue]

Or both?

Oil Pressure switch -
Looking at diagrams, it looks like it will not allow juice to the fuel pump unless there is oil pressure, so it wont help with pressurizing the system and cold starts. Is there a way to wire the switch so the fuel pump will turn on in the run position for cold starts?

Inertia Switch -
This seems like the best safety option and is easy to install.

Im I over thinking or complication this? I dont like being on fire.

Im leaning towards the inertia switch only since it won't cut power to the FP in the run position and help with cold starts.

Any diagrams would help!

Thanks,

 

[Wild horse 75]

Inertia switch is easy. Just find a suitable mounting position and use it to interrupt the ground for the relay. Oil switch is a bit trickier. If you’re running a carb you won’t need the prime since there should be enough in the float bowl to start. If you run EFI you would need to have a second relay that kicks in during crank only to run the pump. Then with a bit of a longer crank it will start. And you will build enough pressure during that crank for it to keep the pump running. If you do run an oil switch make sure it’s for very low pressure. You might be better off running a buzzer for low oil pressure and shutting it off with the key. Same principle but you would be in control. Would also be a fail safe if the oil switch failed you’d still be able to drive it with only unplugging the switch.

 

[Oldtimer]

There are pressure switchs that allow bypass when starting.

See posts 23 & 26 for how ntsqd does his.

Electric fuel pump questions ?

Bumping an older thread...sorry... I'm looking for a diagram of a 4070 setup on a 302. I'm dumb....so I need need a visual of the set up and things I need. Already have the pump and line. Standard fuel tank with Auxiliary tank removed. So a straight shot. I've got people saying pressure...

classicbroncos.com

 

[Broncobowsher]

Oil pressure bypass is easy. The right switch, even a simple diode can be used to run the pump during engine crank.
A possible negative we were discussing last weekend. Friend was in Moab and had a steep down. Enough it lost oil pressure for a moment. If you need the engine running for things like engine braking, power steering, power brakes, then it could get ugly real fast if the engine suddenly stalls. Running EFI, they stall right away. A running engine with oil everywhere inside, has no issues idling for brief periods of time without oil pressure. There is still oil on all the parts, not under load it isn't squeezed out.

I would be tempted to use inertia switch. My wheeling isn't violent enough to worry about accidental tripping. Just make sure it is accessible if you ever need to reset it. They are not weather sealed either.

 

[Ol'Blue]

Im running a qjet carb and recently installed the electric fuel pump with out these two protections. It seems better with cold starts having the system pressurized but maybe that has been my imagination.

Oil pressure switch seems more for engine protections which I can manage by keeping an eye on the gauges etc as I dont want to lose engine power on a grade when oil pressure drops, so Im leaning toward the inertia.

My AAW kit has a dedicated 20 amp fuel pump circuit, so I wasn't planning on running a relay. The pump draw is 10.4 amps.

I didn't realize they weren't weather sealed so Ill have to run the FP ground up into the cab or under the dash somewhere.

 

[ba123]

Or both?

Oil Pressure switch -
Looking at diagrams, it looks like it will not allow juice to the fuel pump unless there is oil pressure, so it wont help with pressurizing the system and cold starts. Is there a way to wire the switch so the fuel pump will turn on in the run position for cold starts?

Inertia Switch -
This seems like the best safety option and is easy to install.

Im I over thinking or complication this? I dont like being on fire.

Im leaning towards the inertia switch only since it won't cut power to the FP in the run position and help with cold starts.

Any diagrams would help!

Thanks,

You're thinking of putting one in, right?

I vote for inertia. I have one, it's easy and it works. Don't need both, although I do have my ecu to cut the engine if oil pressure drops below x, so then maybe I have both but I don't think it's necessary.

 

[Ol'Blue]

Yep, next step in the electric pump install. Im leaning towards just inertia as well.

Trying to find one the interrupts the positive lead as that would be way easier to install under the dash without having to run a neg all the way up in the cab.

 

[ba123]

The ford one is best. It was easiest to order that one from Amazon, don’t remember why but this is where I ordered from:
https://www.amazon.com/dp/B000NU76RM/?tag=classicbroncos-20

It’s my understanding that all Ford inertia switches work with the positive…although that positive might only be the ignition on signal to the relay and not the pump supply.

 

[Broncobowsher]

The inertia switch doesn't care if it is tripping positive or ground. It is a pair of contacts kept closed with a magnet and a ball bearing. You whack it hard enough to knock the ball bearing away from the magnet, the contacts open. Press the reset button, the ball bearings is shoved back into the magnet. Absolutely nothing polarity sensitive about it.

 

[ba123]

Yes, but… I wouldn’t want the actual supply power to my pump depending on that ball.

Enough to switch a relay, absolutely, it just needs conductivity.

 

[Wild horse 75]

The inertia switch should be on the relay power or ground not the pump wire.

 

[Broncobowsher]

Pretty sure that in factory Ford applications, the inertia switch is on the pump power. Including those early EFI systems running 2 pumps with the little accumulator on the frame rail (before they figured out how to do it in tank)

 

[Ol'Blue]

From what I have read the Ford inertia switch is intended for pump power but also read some have shorted/melted so maybe best to install on ground.

So my plan is to run the in tank pump ground all the way up under the dash to the inertia switch to keep it out of the elements and run the power from the AAW provided 20 amp circuit without a relay. AAW tech says I should be good and be able to supply the needed 10.4 amps to the Holley pump.

Im trying the keep with wiring simple as possible but let me know if Im way off base and should suck it up and go with a relay.

 

[Wild horse 75]

The AAW tech is correct. You can absolutely run a small pump off their wire. Personally I like running relays since it will ensure you always have good voltage at the pump. It also allows you to put cutoff switches in the relay power or ground and not need to worry about shorting them out from pump amperage. I think putting a relay in under the dash would be more simple than running the ground wire all the way back to the dash. You can easily use the AAW power wire for both the pump and relay and just use the relay ground for the inertia switch if you want to keep it simple.

 

[ba123]

Do the relay. Easier now than regretting it later. You might second guess that decision and it's simple.

If you want super easy but not inexpensive:
https://www.ronfrancis.com/product/90

You could do:
https://www.painlessperformance.com/wc/80160 (comes with a connector so easier than the one I mentioned earlier)
and
https://www.painlessperformance.com/wc/50102
(looks like $80+ for BOTH) and those pages above have instructions on them as well

https://www.summitracing.com/parts/prf-80160
https://www.summitracing.com/parts/prf-50102

 

[Ol'Blue]

You can easily use the AAW power wire for both the pump and relay and just use the relay ground for the inertia switch if you want to keep it simple.

Ah, I didnt realize this! I thought I had to run another wire to the batt and add a fuse. This makes things easier and keeps all my labeled wire consistent. Will be going with one of the relays and the inertia switch ba123 recommended.

I think I have my plan now. Thanks for all the help.

 

[ba123]

Ah, I didnt realize this! I thought I had to run another wire to the batt and add a fuse. This makes things easier and keeps all my labeled wire consistent. Will be going with one of the relays and the inertia switch ba123 recommended.

I think I have my plan now. Thanks for all the help.

yeah, you can use your existing pump supply as the supply to the relay and the pump out from the relay and just splice it in. Ignition power to the inertia switch to trigger the relay when on (or ground if you prefer).

 

[Wild horse 75]

Ah, I didnt realize this! I thought I had to run another wire to the batt and add a fuse. This makes things easier and keeps all my labeled wire consistent. Will be going with one of the relays and the inertia switch ba123 recommended.

I think I have my plan now. Thanks for all the help.

Yeah it makes the relay more of an electrical switch than a relay. Usually you want to run a new power wire so you can take advantage of higher amperage while reducing the amp load on a switch. But since the wire exists to run the pump already with what should be sufficient amperage for your pump it can just be used as an interruption to the wire that’s controlled by the inertia switch.

 

[ba123]

Yeah it makes the relay more of an electrical switch than a relay. Usually you want to run a new power wire so you can take advantage of higher amperage while reducing the amp load on a switch. But since the wire exists to run the pump already with what should be sufficient amperage for your pump it can just be used as an interruption to the wire that’s controlled by the inertia switch.

Agree that it would be ideal to run a new supply but if it's enough to put you over the edge, so do the first main part and then the new batt supply once you're ready.

 

[Steve83]

Here's the diagram you want:

(click this text)