Fuel Pump Cut-Off Inertia Switch- What are you using ?

kitcarbp · #1 (**permalink**) 06-19-2009, 02:04 PM

Can you advise me which fuel pump cut-off inertia switch you are using or have used on your builds, and the pro/cons based on your experiences?
I am planning a trunk mounted one close to my fuel pump relay.

Thanks

RodgerH · #2 (**permalink**) 06-19-2009, 02:22 PM

I use an engine oil pressure switch in series with a dash mounted toggle switch going to the fuel pump relay. The toggle switch is 3-position "on-off-momentary on". I can hold it in the "momentary on" position and run the pump without the engine running.

Rodger

Michael C Henry · #3 (**permalink**) 06-21-2009, 09:51 PM

I used an Enirtia switch which I understand is a common Ford product . I beleive I ordered it from Ron Francis Wire Works. I installed it on the drivers door post.

MFE III · #4 (**permalink**) 06-21-2009, 10:42 PM

Here's what I used.
http://www.breezeautomotive.com/details.php?prod_id=202
Installed it in my trunk - easy install.

kitcarbp · #5 (**permalink**) 07-20-2009, 09:27 PM

Thanks MFE-III thats what I was looking for, my T-Bird had one in the trunk in the 90's like this one.

RodgerH · #6 (**permalink**) 07-21-2009, 06:33 AM

How much of an impact does it take to trip one of these? How is it measured...g-force?

Do they trip from impact or sudden stop of movement in all directions?

I went with an engine oil presssure switch because I wanted the fuel pump to stop when the engine stopped, regardless of anything else.

Is the inertia switch a better method? Why so?

Rodger

Ron61 · #7 (**permalink**) 07-21-2009, 06:38 AM

I also used the oil pressure and a toggle switch on the dash as I wanted the fuel pump to stop if the engine stopped pumping oil. The toggle was for working on the car and as a back up to the oil pressure switch.

Ron

kitcarbp · #8 (**permalink**) 07-21-2009, 08:57 AM

RogerH, These Inertia switches were developed in late 80's and used in many OEM applications on European and US cars (Ford as an example). I dont know what system GM uses. It is triggered by a severe and sudden impact 10+ G's typically. I think these are still in use. The logic is in severe impacts, (depends on the type) engine could remain running while fuel line(s) is ruptured spewing gas, and driver unable to act. The oil pressure switch type provides a ground or closes the circuit upon engine run (oil pressure above a set point of a few psi). The inertia type opens the circuit milliseconds after impact. The oil pressure activated type allows more cranking voltage and current to be available to the starter for first few seconds of crank since it wont turn on fuel pump until engine produces oil psi above a few #'s, an added benefit. NAPA sells a bunch of styles and sizes (of psi activated) I found.

I did some digging and found the OEM switch I am familiar with. Pegasus Racing sells a new OEM type for about $65 with connector pigtail ready to install. Has a nice rubber boot covering the switch body. Breeze automotive sells a used Ford switch with connector for $25. All electric fuel pumps should have either the oil pressure type or inertia type for safety IMHO.