Thoughts on fuel inertia switch?

[Joe]

When I built my cobra I put one. im Most likely putting one on my 40 but just curious to if any one else is running one on there’s?
thanks

 

[Neil]

The SCTA requires an inertia switch on cars or bikes that run an electric fuel pump. I use an impact switch from a Ford in my car. I think it opens at about 20Gs. If you are involved in a crash- even on the street- and are knocked unconscious, you don't want the electric fuel pump to keep running. You are in enough trouble already-- you don't want to be awash in gasoline as well.

 

[Randy V]

I ran one from a Ford Mustang in my Cobra racecar. There’s a lot of speculation as to proper placement in a race car. Some guys put theres in the tail end of the car like Ford did. I put mine at the bottom of my instrument panel. Some of the guys found that the switch could be a little trigger happy when lightly tapped by a car from behind.

 

[Joe]

I’m running the Ford in my cobra aswell,I have in the back in trunk. I bought another for my 40 build was just curious as to how many people have it in there’s.going through many build threads here it looks like not many.

 

[Neil]

My car has no trunk, it's a mid-engine layout. I mounted my impact switch on the right side of my cockpit; this way, if it trips accidentally I can push the reset button from the driver's seat.

 

[DaveC]

Neil is on it. In my Cobra, I installed the Ford switch in the trunk. It tripped on the track, requiring a tow-of-shame back to the pits. In my GTM, it's in the center console within reach.

 

[David mono]

The amount of impact to trip the switch does very , I'm pretty sure I saw one mounted on the left just below the drivers knee on a Ford mini van 2005 or so. I'd have a look around the junkyard for different mounting points , for personal safety I would mount the switch in arms reach.

 

[Joe]

As mentioned a few above. I agree to keep within arm reach. Never really thought about that. Didn't think there that sensitive as i havnt touched mine in cobra since installed.
Thanks

 

[Malcolm]

I have a 10g switch mounted on the chassis by the door hinge behind the dash. From a Jaguar I beleive but can't remember which one. Only ever triggered once when spun off a track during a competition and went across some very rough ground at speed! Not a lot of effort to fit and a good safety feature to have I think.

 

[David mono]

Something that happened today. Car was running fine and driving around, 3 or 4 stops and restarts later car turns over no start, flat bed drops it of at my place. First thing I do is see if inertia switch was tripped was still down so check out fuel pump relay click click so that seems to work but no fuel pump sound. Back to the inertia switch take that out, it does not sound right hit it to set it off reset hit it off reset now it sounds better ( rattle different ) put switch back in, now fuel pump came on and car started.

The moral of the story is switch may not be in deactivated mode but still is deactivated so check it out anyway.

 

[Ricky]

Personally, I would ground the fuel pump via an oil pressure hobs switch.

If you loose oil pressure due to and engine fault or in an accident the pump stops. - win win in my book and very simple to set up.

 

[Ian Anderson]

Is the inertia switch before or after the pump relay?
before and it is very low current and after could be a large current that had caused heat and malfunction within the switch/contacts

Ian

 

[David mono]

Maybe both inertia and low oil pressure switches would be a good idea. Knocked out driver with engine running spewing fuel after a hit not good.

OEM inertia switch after pump relay, that's the way Ford built it.

 

[DaveC]

I would run the switch before the relay so it sees less amperage, it's just a simple mechanical switch.
Make sure it is mounted vertically in the OEM orientation. Is it the Ford switch? Shouldn't fault like that, there are 100's of thousands of them out there that aren't leaving Focus drivers stranded... I'd replace it.

 

[David mono]

It's in a Ford just the way it left the factory with the original switch in its factory location. Other's have experienced the same thing, I have a few switches on the shelf and will put one of those in.

 

[Frank Catt]

I also strongly recommend a fuel pressure dump valve if running carbs.

 

[Lee Patterson]

Something like this is what I am looking at: https://painlessperformance.com/product/rollover-safety-switch-part-no-80160/

 

[JP Verweij]

I run none in all my cars.. all pre 80s, dont fancy anything modern.
Cause it didn't have them back in those days.
Whats not there will not cause issues..
I dont have ABS, ESP, Airbags, Lane assist and whatever they found in this new age.

 

[Frank Catt]

JP, when you are sitting in your GT40 all strapped in and the doors closed , when you press the starter and see that immediate flash of flames from your carbs just behind your head, when panic sets in and you have get out of the belts, get the door open, get yourself out of the car, open the rear body and find a fire extinguisher, realise the pumps are still running and you can’t reach the kill switch, then you will know why I always fit a fuel pressure dump switch, just a simple push button might save your car and perhaps your life .

 

[DaveC]

I run none in all my cars.. all pre 80s

Don't need one for mechanical fuel pumps. Not sure why you wouldn't spend $30 to lessen the probability of a fiery death.
You do you.
But ask your next 5 passengers if they would prefer that the car they are riding in keeps pumping fuel in the event of an accident, or would prefer a $30 device that would *almost* definitely cut off the fuel flow during such an event.