crash fuel cut

[mellonman]

i see a few threads about 12v mod and they say they fit realys to stop the fuel pump in case of a crash, yes sounds great

but how does the car know when you have had a crash?

or should i say what makes the fuel ecu cut voltage to the pump.

[add heywood]

Sometimes with the 12v mod the pump is constantly on with ign position 1. They mean they add a relay so it primes and then only runs when engine is running

[mellonman]

im not 100% but would you really need a relay for that here is a drwing i have done of what i think they are doing let me know what you think

 

now could you not just wire the 12v feed to the 9v vairable voltage from the ecu to the pump and disconnect them from the ecu? this would still then work from the ignition right

[AJI]

I had an old Sierra XR4x4 a good few years ago for road rallying, this had a fuel cut on it. I think it worked on a ball and spring method whereby it took a certain amount of g-force impact for the ball to compress the spring in order a metal-to-metal contact was made with a circuit. This circuit contact then told the ECU to cut the fuel pump.

To re-set this circuit there was a switch within the boot of the car.

 

I kept setting off the crash fuel cut off when I got airborne on many of the road rally routes. (Ah...the good ol' days).

[mellonman]

that is interesting as i have had a crash in the supra twice now and the car had cut out both times,makes sence that they do actually have a switch impacts.i just thought it was because of the auto box and facing the wrong way and hitting a curb