Fuel Shutoff in accident?
Fuel Shutoff in accident? How are you guys doing the retro fits handling the fuel pump shut off in case of a rollover/accident. I don't think there is any pcm function that does it but don't know for sure. The fuel pump has a relay that engages once the ignition is turned....but what triggers it to shut the fuel off, and how??
I'd think that it would need an inertia switch to sense g forces. Any input here?
I'd think that it would need an inertia switch to sense g forces. Any input here?
Joined: Nov 2001
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From: Texas and Qatar
Fords have used fuel pump disabling intertia switches for years, one of these could possibly be used to disable the fuel pump relay in a retrofit application. As far as GM crash detection, I was under the assumption that the engine shuts off in a crash, although I could be mistaken - such a system in the OEM vehicle would have to go through the SRS system I'm sure.
Joined: Nov 2001
Posts: 3,043
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From: Texas and Qatar
Good question... never really thought about driving stick and the engine likely stalling in a crash. The computer will cut fuel if the engine stalls.
In an auto... ya... an inertia switch would be the best thing.
In an auto... ya... an inertia switch would be the best thing.
I've been looking at these links...I think that you could rob an inertia switch out of a Ford at the junk yard and be in cheap too.
http://www.smartracingproducts.com/p...uelshutoff.pdf
http://www.pegasusautoracing.com/pro...s.asp?RecID=87
http://www.smartracingproducts.com/p...uelshutoff.pdf
http://www.pegasusautoracing.com/pro...s.asp?RecID=87
I have them in two of my cars that I got from the junk yard, never had a problem with either of them, except the time I was building my '33 and had hit the body with a hammer near the switch and tripped it, then the next day I couldn't start the car. I was tracing power on wires until I remembered I might of hit the inertia switch! 
I never like inertia switches, since they've been know to trip, for non-accidents, like hitting pothole in PA. The fuel pump relay shuts off the fuel pump as soon as the motor stops running, that meets all the Federal Vehicle Safety Standards and thats good enough for me. You don't fix things that are not broke, by making them more complex
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Joined: Nov 2001
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From: Texas and Qatar
I never like inertia switches, since they've been know to trip, for non-accidents, like hitting pothole in PA. The fuel pump relay shuts off the fuel pump as soon as the motor stops running, that meets all the Federal Vehicle Safety Standards and thats good enough for me. You don't fix things that are not broke, by making them more complex
I've cut 1.34 60' times in my Mustang without the intertia switch tripping (I think that is about 2 G's avg accel), and in my younger days jumped a $300 Ford Escort over several railroad tracks without tripping it. (long enough air time to look at passenger and say WTF) So the trigger happy switches seem to just be random to me and isolated cases.
In moderating this section and working on cars in general for 18ish years, I've seen some rubber line and hoseclamped EFI "fuel systems" that I wouldn't trust on a tractor. Anytime someone engineers their own fuel system it does not meet safety standards anymore unless left OEM. There are a ton of things that can go wrong in a crash, injectors can be pulled from the fuel rail spraying fuel over the engine, pressurised or return fuel lines pulled off or cut over guard rails, brush, etc. It would take a few seconds to kill the engine as the fuel system depressurizes while the fuel pump is still running, and even then the ECM does not power it down instantly. This is all worst case thinking of course but all possible.
I think some sort of crash detection fuel disabling device is a good idea even if it is troublesome, further... some guys don't let the ECM control the fuel pump for whatever reason. I'm not singling you out or anything, just discussing. Remember, I grew up in NE PA.
This thread has me wanting to research retrofitting intertia switches more and more.
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The pcm controls it. If you have it wired into a factory harness. It will keep the fuel pump going until the engine stalls. Unless you run an inertia switch like some of the Fords do.
I have over 30'000 miles on my '33 and have never had mine trip, and I've hit potholes big enough to bend wheels. 
I put mine in for cheap insurance, I don't think it made anything too complicated, it's only two wires inline to the pump, and if I have to leave the car somewhere (ie- motel parking lots in towns I'm not familiar with, you never know if your in a "good" part of town or not) I'll hit the switch to make the car just a little bit harder to steal.
I put mine in for cheap insurance, I don't think it made anything too complicated, it's only two wires inline to the pump, and if I have to leave the car somewhere (ie- motel parking lots in towns I'm not familiar with, you never know if your in a "good" part of town or not) I'll hit the switch to make the car just a little bit harder to steal. 
TECH Resident
Joined: May 2004
Posts: 792
Likes: 2
From: SoCal
Glad to see people discussing this. I started a thread regarding an inertia switch a couple of years ago, but no one seemed to care (then). Anyway, it would seem to me that it's worth the extra effort to install one from a safety perspective. Though the GM PCM shuts down the fuel pump once the engine stalls, I've seen a few accidents where the engine kept running after an impact.
True that the Ford switch can be overly sensitive, but perhaps Joseph's explanation of trigger happy switches can be remedied with a replacement. A friend had a T'bird SC that got bumped in a parking lot and it failed to start afterward; it likely had one of those trigger happy switches. I think on that car it was mounted in the trunk; my Explorer has one mounted under the dash on the passenger side (it's never tripped in the past 12 years).
Andy1
True that the Ford switch can be overly sensitive, but perhaps Joseph's explanation of trigger happy switches can be remedied with a replacement. A friend had a T'bird SC that got bumped in a parking lot and it failed to start afterward; it likely had one of those trigger happy switches. I think on that car it was mounted in the trunk; my Explorer has one mounted under the dash on the passenger side (it's never tripped in the past 12 years).
Andy1
Glad to see people discussing this. I started a thread regarding an inertia switch a couple of years ago, but no one seemed to care (then). Anyway, it would seem to me that it's worth the extra effort to install one from a safety perspective. Though the GM PCM shuts down the fuel pump once the engine stalls, I've seen a few accidents where the engine kept running after an impact.
True that the Ford switch can be overly sensitive, but perhaps Joseph's explanation of trigger happy switches can be remedied with a replacement. A friend had a T'bird SC that got bumped in a parking lot and it failed to start afterward; it likely had one of those trigger happy switches. I think on that car it was mounted in the trunk; my Explorer has one mounted under the dash on the passenger side (it's never tripped in the past 12 years).
Andy1
True that the Ford switch can be overly sensitive, but perhaps Joseph's explanation of trigger happy switches can be remedied with a replacement. A friend had a T'bird SC that got bumped in a parking lot and it failed to start afterward; it likely had one of those trigger happy switches. I think on that car it was mounted in the trunk; my Explorer has one mounted under the dash on the passenger side (it's never tripped in the past 12 years).
Andy1
Fuel pump run on after a wreck is the very same reason NASCAR won't allow electric fuel pumps on the cars.
TECH Resident
Joined: May 2004
Posts: 792
Likes: 2
From: SoCal
I agree. I used to hate these switches when I worked on a few friends' Fords because it was one more thing to go wrong / troubleshoot. Being older and wiser I'm glad they are available. It's just cheap insurance.
Fuel pump run on after a wreck is the very same reason NASCAR won't allow electric fuel pumps on the cars.
Fuel pump run on after a wreck is the very same reason NASCAR won't allow electric fuel pumps on the cars.
I like that the later switches have provision for a light that signals when it's been tripped.
Andy1
Summit and Autozone has them for $29. That's probably cheaper than driving to and from a pick-n-pull (30 miles in my case), walking around, finding one, removing it, etc, etc.
I like that the later switches have provision for a light that signals when it's been tripped.
Andy1
I like that the later switches have provision for a light that signals when it's been tripped.
Andy1
BTW, you forgot HOPING it is good since most people can't field test the unit accurately.
This is even a better idea for the carb'd guys. My fuel pump runs whenever my key is on. I can see how this would be a serious problem in an accident. Does anyone have the years/models or a P/N for the fancy switch with the light?
TECH Resident
Joined: May 2004
Posts: 792
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From: SoCal
http://www.fordmuscle.com/forums/all...ia-switch.html
Apparently the NO contact closes once the switch is tripped, and becomes
+12V in order to power an indicator light untill the switch is reset.
I guess you could field test it by smacking it with a rubber mallet (but not too hard :-)). That Ford site metions 10G's to trip it.
Andy1
Joined: Nov 2001
Posts: 3,043
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From: Texas and Qatar
http://www.fordmuscle.com/forums/all...ia-switch.html
I guess you could field test it by smacking it with a rubber mallet (but not too hard :-)). That Ford site metions 10G's to trip it.
Andy1
I guess you could field test it by smacking it with a rubber mallet (but not too hard :-)). That Ford site metions 10G's to trip it.
Andy1
BTW, your link didn't work.