electric fuel pump and oil pressure relay

[Moto Carlo]

I did a search and could not find this. Seems it would be an old question so sorry for recycling it.

Often hot rod guys use oil an pressure relay screwed into the oil pressure sensor at the dizzy. The idea is when there is no oil pressure, the electric fuel pump stops.
So it stops pumping gas in an accident if the key were still on. The question: Do you guys do this and any info on brand and mounting? 

(On old Porsches I have used the Revolution Relay that works electronically off the tach. But the current relay I have has a problem, perhaps because of the coil I am using with my electronic ignition. . So looking for alternatives and I remembered the oil pressure relay.)

As always, thanks.

[tahoedon]

I got mine from Pegasus Auto Racing Supplies.  Part #1109.

[Son of Marty]

The oil pressure switch has largely been replaced with a inertia switch which will break the circuit with a large sudden g load in any direction. A oil pressure switch would require a start bypass for any fi system and could leave the car running in some circumstances such as the fuel in the float bowls with carbs or a ruptured return line with fi spilling fuel until the engine stops.

[John76]

I'm trying to imagine a situation where a car is crashed severely enough to sever a fuel line but the engine would continue to run.

Is this only an issue with automatics?  Any manual trans car would stall the engine (zero oil pressure) in a sudden stop....unless the driver shifts into neutral prior to the unfolding calamity.  Any thoughts???

Easy enough to add or supplement the oil pressure switch with an inertia switch. The inertia kill switch has only two terminals, since it doesn't need the "S"  terminal on the oil switch. Both types are readily available.

 

[Son of Marty]

I'm not saying this occurs often, only that it can be eliminated with the more modern approach. By any measure a oil pressure switch is way better than no switch.   

[KFunk]

I used a vdo brand pressure switch for a while, but the pump kept cutting out while idling after warmed up.  I could hear it shutting off, and just revved it if I wanted to make sure the engine would keep running, but it was kind of annoying.  I think my old beat stock engine just couldn’t make enough oil pressure to keep it triggered.  After my rebuild it may do better, but haven’t tried it.

[TobyB]

The inertia switch can come out of any 80's and 90's Ford product- the Taurii and other blobs had a big label in 

the driver's side trunk pointing you in the right direction.

 

It's high current, so it can interrupt the power right at the pump, nothing fantsy needed.

 

t

 

Edited April 26, 2020 by TobyB

[Stevenc22]

I bought a ebay inertia switch. Seems to work fine. Easy to reset.

 

https://www.ebay.com/i/183727849647?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=183727849647&targetid=883484275562&device=c&mktype=pla&googleloc=9027583&poi=&campaignid=9343999134&mkgroupid=101452701304&rlsatarget=pla-883484275562&abcId=1139336&merchantid=6296724&gclid=CjwKCAjwnIr1BRAWEiwA6GpwNe9jnHgubEphvIQEMUL3fLEZdsNNOw_OCm3MXUgi65S0NfHqgIUqQRoCeboQAvD_BwE#

[Moto Carlo]

Thanks guys. The inertia switch - $9. Wow!

Hate to seem the Luddite, but I'm not expecting directions with the switch. So ... it appears that the two leads would simply interrupt the  positive line  going to the fuel pump. And the switch interrupts that line if the car get enough of a jolt to trip it. Correct?
How can it be that easy and cheap. Love it!
And last , is it sensitive enough to mount it in the trunk by the fuel pump?  How about speed bumps / pot holes? 

This is great info and seems the way to go. Thanks everyone.

Edited April 24, 2020 by Moto Carlo

[Stevenc22]

Mine is mounted in the trunk next to the fuel pump. I have never tripped it regular driving.

[Moto Carlo]

Thanks Steve. I am going to give it a try. ?

[Stevenc22]

Here is mine. Also useful to disable the fuel pump when doing electrical work that requires the ignition to be on.

[jimk]

Location, out of the way.

[TobyB]

One thing that Jim's picture reminds me-  mounting angle matters.

 

The switches have a heavy ball bearing sitting in a cone. 

There's usually a magnet at the bottom to prevent false tripping.  

Whenever you stop too fast, inertia overcomes gravity, the ball

climbs out of the cone, and the switch trips.

 

Since the cone's partially using gravity to calibrate it,

the 'reset' button should be pointed straight up.  In the

Ford version I've taken apart, it's a round cone, so rotational

orientation doesn't matter.  But 'up' does.

 

t

disorientated

[Moto Carlo]

Thanks Toby.