inertia fuel cutoff switch for an EFI system?? - anybody install one of these?

Discussion in 'High Tech for Old Iron' started by elagache, Jan 23, 2013.

  1. elagache

    elagache Platinum Level Contributor

    Dear V-8 Buick early adopters,

    Someone on the Station Wagon Forum suggested that I add what is called an "Inertia fuel cutoff switch" to the EZ-EFI installation for my trusty 1965 Buick Special wagon and its assertive JW masterpiece big-block engine.

    I never heard of such a thing. Digging around the Internet, what I've learned is that these switches relay upon some sort of calibrated mass ball that will break from its support for a given acceleration/deacceleration. Power to the EFI pump is routed through this device. The thinking is that if the car is suddenly brought to a stop in an accident the ball will break lose and that will shut off the EFI pump even if the car still has electrical power and thus the pump would otherwise continue to run. Otherwise, these high-power pumps could spew out a lot of gasoline in a short period of time and greatly increase the risk of a post accident fire.

    It certainly seems to be a new idea. Ford uses them as well as some imports. I didn't see any reference to GM or any aftermarket inertia switch suppliers.

    Has anybody thought about incorporating such a switch in their aftermarket EFI installations? If so, any suggestions on switches to use, installation ideas, etc. ?

    On the flip side, would you not bother to install this? If so - why?

    Opinions solicited! :Smarty:

    Cheers, Edouard :beer

    P.S. I don't know if these switches are sensitive enough to be set-off by the accelerations in drag-racing. There are instructions on how to disable for demolition derby cars. Yeah, I think you would need to do disable the switch for that sort of driving!! :Brow:
     
  2. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    I keep thinking about installing one but haven't. Ford just offers one that is easy to adapt to the aftermarket, I believe most others have one somewhere or another.

    Paul and others will probably know for sure, but doesn't the EZ-EFI 1.0 control the fuel pump relay?

    The MegaSquirt controls the ON/OFF of the fuel pump (at least when wired properly), and the way it goes is if the engine is running it'll keep supplying fuel, if the engine stalls/shuts off the megasquirt shuts the fuel off a five-ten seconds later. I never timed it. If the high pressure fuel line was seriously compromised, then fuel pressure would drop, the injectors wouldn't fire, engine would stall and the MS would shut the pump down. If the line is only marginally compromised then the fuel pump may continue to run as long as the engine was running.

    The safest thing to do is install the switch inline with the fuel pump power wiring, but the pump won't run long if the engine isn't running or if the fuel line is significantly compromised.
     
  3. pmuller9

    pmuller9 Well-Known Member

    The EZ-EFI has a fuel pump control output that controls the power relay for the fuel pump also.

    Not sure how long it takes to shut the fuel pump off after the engine stops.
    Edouard will have to give us that report.

    It certainly wouldn't hurt to have a inertia fuel cutoff switch just in cases where the car has been hit or ran into something and the engine is still running.

    Paul
     
  4. black70buick

    black70buick Well-Known Member

    I have an older Holley Projection 4DI TBI system that I plan on installing. I also have two ford inertial switches that I pulled from some junk yard cars. I will be using one in direct line with the fuel pump power. :TU:
     
  5. elagache

    elagache Platinum Level Contributor

    Okay, I'll look into this. (Re: inertia fuel cutoff switch for an EFI system??)

    Dear Randall, Paul, Chad, and V-8 Buick leading edgers,

    Thanks for the good advice! :TU: Okay, so I need to figure out how to get my hands on one of these switches and wire it into the fuel-pump power supply.

    I'll add it to my copious "to-do" lists!

    Cheers, Edouard :beer
     
  6. black70buick

    black70buick Well-Known Member

    Re: Okay, I'll look into this. (Re: inertia fuel cutoff switch for an EFI system??)


    Hopefully it isn't too difficult. I quickly checked ebay and found a GM one:
    http://www.ebay.com/itm/AC-Delco-D1...Parts_Accessories&hash=item19d8657325&vxp=mtr


    The ones I have I pulled from a late 90's Ford Torus and Escort and look like this:

    http://www.ebay.com/itm/Mercury-Gra...Parts_Accessories&hash=item460abf6a7b&vxp=mtr

    Pretty simple to install, but make sure it is solidly mounted to the frame/body.

    Good luck.
     
  7. DaWildcat

    DaWildcat Platinum Level Contributor

    Eduoard,

    Thanks for bringing up this topic. I think it's important for just about everyone who has added an electric fuel pump to their car, even carbureted engines.

    For many years there's been advice and circuit diagrams published that an oil pressure cut-off switch should be a part of the electric fuel pump circuit, so that if engine oil pressure drops to zero, the fuel pump circuit is switched off as well in the event of a collision or rollover. I think most folks don't bother with this, because after a car sits with the carburetor's float bowls dry, they don't want to have to have a parallel momentary switch to prime the carb for startup.

    I'm one of them. I don't have either safety measure in my Buick now and it needs to be remedied. So much for the fuel system engineer, eh?

    Devon
     
  8. elagache

    elagache Platinum Level Contributor

    Not as easy as it looks, (Re: inertia fuel cutoff switch for an EFI system??)

    Dear Chad, Devon, and V-8 Buick early adopters,

    Hmm, honestly I've been busy with other wagon details and haven't looked much more into this, but I've gotten some feedback that disturbs me about this idea.

    My friend on the Station Wagon Forum mentioned that these switches are somewhat sensitive. Even hitting a bad pothole could be enough to trip the switch. So there I am vacationing 2000 miles from home and I hit a bad pothole - how to I get home? Sorry that's not a risk I'm willing to take.

    Even in the accident da' trusty wagon had in 2010, the car was able limp home like the trooper she is. If you have an accident, but the car is sufficiently undamaged that it can move some on its own, it may be imperative to move the car even a short distance to move out of flowing traffic and avoid a potential follow-up accident.

    All this leads me to conclude that if I were to install a inertia fuel cutoff switch, I would need a manual override for cases like this. That is a bit awkward to do in a wagon if you need to easily access the override in an emergency.

    Devon now adds:

    Well, this is now sounding plenty complicated and getting beyond the realm of amateurs. If you need a circuit like this, I don't think it would be too much harder to detect whether or not the fuel pump pressure is zero because the ignition has been turned off instead of zero while in operation. It seems to me I really want an aftermarket manufacturer to take the time to consider all these details and give a solution that is properly designed. If I try to design this on my own - I'm afraid I'll make things worse rather than better even with all the help I can glean from you'all.

    Related to all this is another puzzle I'm feeling. These inertia fuel cutoff switches aren't used by all auto makers by a long shot. They appear to common on German cars and some Japanese cars. However, Chrysler and GM don't appear to use them. Does anybody know what these automakers are doing? I suppose they could use accelerometers in the computer electronics like are found in laptops to protect hard drives.

    This sure looks like an item that will require some more research before actually trying to install one.

    Thoughts?

    Cheers, Edouard :beer
     
  9. DaWildcat

    DaWildcat Platinum Level Contributor

    Edouard,

    The only time I tripped an inertia switch when it shouldn't have was hitting a big rock with the left tires while under heavy acceleration in a 1989 Ford Taurus SHO. The engine quit. The nice thing about this switch is that it features a reset button. I coasted off to the shoulder, got out, opened the trunk and pressed the reset button and was on my way again. See big red button:

    [​IMG]
    [​IMG]



    Devon
     
  10. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    Yup, they have a nice reset button on them. Simply an annoyance, that may not even come up. You won't know until you try it, and they are simple to remove or remount if they are too sensitive.
     
  11. black70buick

    black70buick Well-Known Member


    Devon, I agree completely. :Brow: This is why I have two, I need to install one in the Riv (even presently with the Carb set up). The second switch is for what ever project comes next :Do No:

    Edouard,
    Unless you have low profile tires and have zero suspension, the likelihood of tripping the switch in normal or aggressive driving is very low. Remember these are even installed in compact cars not well known for a comfortable ride. :pp

    I won't go into much detail, but I have one mounted to a golf cart frame, it took a direct hit to the frame to trip the switch (one pound hammer, a standard nail hammer could not do it). Dropping the cart 1 foot from the ground with full suspension was still not enough to trip it.

    btw, GM uses the ECM (but the logic is the same as my '70 Riv which runs a electric fuel pump - oil pressure drops fuel pump is shut off), my Holley 4DI projection system kinda operates the same way but when oil pressure drops it only limits the engine to 2500RPM...I figure using the inertia switch is like having a fire extinguisher, better safe then sorry and not that entirely difficult to install. The ford switches that I have do have reset buttons.

    http://wiki.answers.com/Q/Where_is_an_inertia_switch_on_a_1994_Cadillac

    "There is no "inertia switch" like on the FORD's. The fuel pump is activated by a dual circuit... engine's computer (PCM) activates the fuel pump relay which in turn powers the fuel pump & after the engine's oil pressure reaches 4.5 lbs, the oil pressure switch also provides power to the fuel pump. Normally, the PCM will prime the fuel pump for about 3-4 seconds when the ignition key is cycled from "Off" to "RUN". The computer keeps the fuel pump relay on as long as there is a RPM signal going to the computer. Totally different from the FORD concept where there is a "JAR" switch or inertial switch located in the trunk of most passenger cars & in the passenger's "kick panel" on most trucks. Here the switch is turned off in case of a violent "jolt" to the car ... like a rear end collision."

    -Chad
     
  12. elagache

    elagache Platinum Level Contributor

    Didn't know about reset switch (Re: inertia fuel cutoff switch for an EFI system??)

    Dear Devon, Randall, Chad, and V-8 Buick early adopters,

    Oops, my misconception. The way these switches were described to me I envisioned that the tripping process was caused by the physical failure of some connection to the mass ball. So as I imagined the switch, a part would need replacement. The reset button does make the idea much more appealing.

    Golly I made a quick stab at this URL you posted, but I still don't understand what a GM car would do in the case of a jolt caused by an accident. Is the expectation that some other engine indicator would cause the ECM processor to shut off the fuel pump?

    Oh well, indeed it looks like an good idea to put in one of these inertia fuel cutoff switches. Although, using one from a Ford!?! :rolleyes: - I dunno' :Brow:

    Cheers, Edouard :beer
     

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