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Thread: Fuel Pump Shut Off After Crash!

  1. #1
    Senior Member fastzrex's Avatar
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    Fuel Pump Shut Off After Crash!

    While trying to decide which direction to go with a fuel tank (gen 2 FF, Boyd original, Boyd modified), a question came up about what happens if the 818 is in a crash. Does the fuel pump remain energized? In looking in the wiring, I do not see an actual inertia switch and in the WRX I suspect actuation of the air bag sensor also kills the fuel pump.

    Am I missing something or do I need to plan for a switch to kill the pump in a case of an accident?
    ~ Mark

    818C S/N 429ES: Start Date 1 September 2016
    2001 NB Miata LS3 V8 440 rwhp
    2004 Miata MazdaSpeed Factory Turbo

  2. #2
    Senior Member Canadian818's Avatar
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    A kill switch for all power would ease all worries.
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  3. #3
    Senior Member Bob_n_Cincy's Avatar
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    Quote Originally Posted by fastzrex View Post
    While trying to decide which direction to go with a fuel tank (gen 2 FF, Boyd original, Boyd modified), a question came up about what happens if the 818 is in a crash. Does the fuel pump remain energized? In looking in the wiring, I do not see an actual inertia switch and in the WRX I suspect actuation of the air bag sensor also kills the fuel pump.

    Am I missing something or do I need to plan for a switch to kill the pump in a case of an accident?
    Fastzrex
    During this project I became intimately familiar with the wiring. In our years of Subaru's, there is no connection between the air bag system and the ECU/fuel pump. There also in NO inertia switch for the fuel pump.
    Bob
    818S #22 Candy Blue Frame, Front Gas Tank, 2.5L Turbo, Rear radiator, Shortened Transmission, Wookiee Compatible, Console mounted MR2 Shifter, Custom ECU panel, AWIC soon
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  4. #4
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    An inertia switch is a good idea and there are many to choose from for your custom installation. Expect to pay around $65 maybe less. Ford used a variety of these that you should be able to make work. A search from any of the online auto parts companies, eBay, or Amazon will show you what's available. I'm building a much different car than yours and will use it to drag race. Besides a master battery and alternator disconnect my fuel pump will be wired through an oil pressure switch (kills the fuel pump when oil pressure is under 7 PSI), an inertia switch, and a check valve on the fuel supply line that shuts off in case a line is ruptured or ripped off in a crash. I've been burned (second degree) many times and take fire safety very serious now. Having the blisters on my burned skin scrapped off every other day for weeks changes your attitude from that won't happen to me to what can I do to mitigate the hazard. Spend the $65 and play it safe.

  5. #5
    Senior Member fastzrex's Avatar
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    Thanks for the reply and recommendation. With the fuel tank so close to the passenger compartment, it makes sense to me to have at least a fuel pump shutoff and a vent roll over. I found several switches at vendors i have used before.

    Quote Originally Posted by NAZ View Post
    An inertia switch is a good idea and there are many to choose from for your custom installation. Expect to pay around $65 maybe less. Ford used a variety of these that you should be able to make work. A search from any of the online auto parts companies, eBay, or Amazon will show you what's available. I'm building a much different car than yours and will use it to drag race. Besides a master battery and alternator disconnect my fuel pump will be wired through an oil pressure switch (kills the fuel pump when oil pressure is under 7 PSI), an inertia switch, and a check valve on the fuel supply line that shuts off in case a line is ruptured or ripped off in a crash. I've been burned (second degree) many times and take fire safety very serious now. Having the blisters on my burned skin scrapped off every other day for weeks changes your attitude from that won't happen to me to what can I do to mitigate the hazard. Spend the $65 and play it safe.
    ~ Mark

    818C S/N 429ES: Start Date 1 September 2016
    2001 NB Miata LS3 V8 440 rwhp
    2004 Miata MazdaSpeed Factory Turbo

  6. #6
    Senior Member fastzrex's Avatar
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    Thanks for your reply and knowledge of Subaru systems. I suspected that the ECU would see the air bag switch send a crash alert and possible turn off the fuel pump through the Fuel Pump Control relay. Since there is no air bag in the 818, I guess I will have to do something else.

    As the passenger compartment is so close to the tank, I just want to make sure there was a way to turn off the fuel pump, and will integrate an inertial switch like Ford products use for this purpose.

    Quote Originally Posted by Bob_n_Cincy View Post
    Fastzrex
    During this project I became intimately familiar with the wiring. In our years of Subaru's, there is no connection between the air bag system and the ECU/fuel pump. There also in NO inertia switch for the fuel pump.
    Bob
    ~ Mark

    818C S/N 429ES: Start Date 1 September 2016
    2001 NB Miata LS3 V8 440 rwhp
    2004 Miata MazdaSpeed Factory Turbo

  7. #7
    fasterer and furiouser longislandwrx's Avatar
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    In factory form the fuel pump controller will shut off the pump if the engine stops running. It will not shut off in a crash if the engine is still idling.
    A well stocked beverage fridge is the key to any successful project.

  8. #8
    Senior Member fastzrex's Avatar
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    Thanks for the making that clear. I think I will include an inertia switch for my build.
    ~ Mark

    818C S/N 429ES: Start Date 1 September 2016
    2001 NB Miata LS3 V8 440 rwhp
    2004 Miata MazdaSpeed Factory Turbo

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