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Thread: anyone use a fuel pump kill switch?

  1. #11
    Registered Member chevynut's Avatar
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    I'm sure there are LOTS of accidents where the engine keeps running after impact. That's why car manufacturers use impact sensors to shut off the fuel pump. As I said above, you can completely sever a return line or partially sever a pressure line and still have fuel pressure. My in-tank fuel pump is rated at 255 LPH (67 GPH or 1.12 GPM) at EFI operating pressure and that translates to a pretty big leak with the engine idling.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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  2. #12
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    I think the inertia switch is a must have too. In an accident, that could come in very handy, but it's too bad their wasn't a good way to know when you have a simple fuel leak undetected too, until it bursts into flames. That seems to happen a lot! I've been caught more than once with a bad mechanical fuel pump spraying gas right onto the headers. Which you can only see with the hood up, with the engine running, since it instantly burns off. I don't know if it makes a difference, but as far as location I am going to mount my crash switch in the rear near the tank/pump. If it has an extra pair of contacts, I would connect them up to an indicator light, so you know WTH made your car quit running. While I'm at it I will do something on the cooling system to know when you've just dumped all of you coolant on the highway. That's happend to me too many times, and everything seems fine, because the temp gauge don't work heated by air.
    Last edited by 55 Rescue Dog; 12-17-2019 at 04:10 AM.

  3. #13
    Registered Member WagonCrazy's Avatar
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    I am going to mount my crash switch in the rear near the tank/pump. If it has an extra pair of contacts, I would connect them up to an indicator light, so you know WTH made your car quit running.
    Good thoughts...but since the switch is resettable, i'm not going to bury it...but put it in the center console near all the other wiring so i can get to it. And good suggestion to add a simple led light, to know quickly if it tripped or not.
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

  4. #14
    Registered Member chevynut's Avatar
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    Quote Originally Posted by WagonCrazy View Post
    And good suggestion to add a simple led light, to know quickly if it tripped or not.
    You'll know quickly that the switch tripped because the engine will die. These switches usually have three contacts, common, NO, and NC but often only two are used. You could wire in a light, but it would only come on when the fuel pump is supposed to be running and the switch is tripped. Running it to a buzzer or chime might be a slicker alternative and you wouldn't have to actually SEE it. Bit then again it might be easier to just remember to check the switch if the car won't start.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  5. #15
    Registered Member chevynut's Avatar
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    Hey Paul, I'm curious how you ended up wiring your fuel cutoff inertia switch into your fuel pump circuit. It looks like Ford wires them directly in series with the pump. However, I was just ordering new terminals so I could wire mine and I realized it might be better to wire it into the coil side of the fuel pump relay. That way the fuel pump current wouldn't have to run through the switch and potentially cause a voltage drop to the pump. I wonder why Ford didn't wire it that way.

    I think I'm going to put my inertia switch under the rear seat so it's easy to get to, and install an audible device to indicate when the switch is tripped. Hope I never hear it.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  6. #16
    Registered Member WagonCrazy's Avatar
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    It looks like Ford wires them directly in series with the pump. However, I was just ordering new terminals so I could wire mine and I realized it might be better to wire it into the coil side of the fuel pump relay.
    I'm wiring mine "in line" with the ECM signal wire -to- coil side of the fuel pump relay. For this same reason (not to have the inertia switch carrying the full amperage thru to the fuel pump).

    I found a cheap led light+buzzer on amazon and ordered that.

    I'm using that 3rd available pin (in the inertia switch) to energize the light/buzzer (so that when I hear it, and open the center console lid to investigate, i'll quickly see the light on, buzzer buzzin' and can quickly hit the reset switch.

    I'll post a few picks when I get it all wired in.
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

  7. #17
    Registered Member chevynut's Avatar
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    Sounds like we're thinking alike Paul. Looking at my switch it appears that it has a steel ball held in place by a magnet, which holds the switch closed. When the ball is yanked off of the magnet by a shock, the switch opens. Then it has to be manually reset by pushing the ball back into the magnet. I would be sure to mount it vertically as that should help prevent false tripping due to potholes or rough roads. Hope we never have to worry about whether these things work or not.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  8. #18
    Registered Member WagonCrazy's Avatar
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    Got the fuel pump shutoff "inertia" switch wired in and working. However, my plan was to use the same signal voltage coming from the ECM to make the little LED light/buzzer sound off when the switch is triggered.
    But the light/buzzer didn't work after it was wired up in the nomad. (it DID work on the bench with 12 volts pushed thru it). Turns out the ECM signal output voltage for the fuel pump circuit is only about 5 volts, which is enough to trigger the fuel pump relay to shut off, but not enough to power up the light and buzzer. I'm gonna have to rethink this one and wire the light/buzzer to a full 12 volt source.
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

  9. #19
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    Pretty cool, and a good idea. You just need to run one more wire like you found out.

  10. #20
    Registered Member chevynut's Avatar
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    How is “one more wire” going to solve the problem with only 3 terminals on the switch? I’d make sure the ECM is doing what you think it’s doing first. I would have expected the ECM to ground the relay coil. I’m pretty sure mine does.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

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