best way to disable the car electronically

Discussion in 'ELECTRICAL' started by dark_knight, Apr 6, 2012.

  1. dark_knight

    dark_knight Registered User +

    i'm not sure this is a taboo topic to discuss here but i was wondering, what's the best way to disable the car (say when installing an alarm system)..? i'm thinking more of disabling the car both from starting and also disabling it when already on the move.
    - disabling the fuel pump..?
    - disabling the ignition (ignitor)..?
    - disabling the ecu..? (not sure how)
     
  2. pilgrim_fgau

    pilgrim_fgau Paid Member

    I was talking this over with Jay the other day and he pointed out something quite important to think about, is how secure the fittings/switches/components are, to ensure that there is NO CHANCE of the switch changing state whilst driving, leading to failed power steering and failed braking power.
     
  3. aidan

    aidan Registered User +

    id be cutting the spark anyway very easily done just splice into the feed from the ecu to the igniter via a switch hiden somewhere
     
  4. dark_knight

    dark_knight Registered User +

    i'd be least worried about PS and braking since you can always stay in gear and keep your engine running to maintain vacuum for braking and to keep the crank running to power your PS pump. i'd be more concerned about other electrics dying.. :/
     
  5. dark_knight

    dark_knight Registered User +

    ignition cut-off

    will cutting the ignition mean the injector duty cycle is still running thus flooding the chamber with gasoline..? how can i avoid that..?
    also, would this mean i splice into the IGT feed into the ECU..? i've got a glanza so this should be pin22 on connector1.
     
    Last edited: Apr 6, 2012
  6. dac69er

    dac69er Super Moderator

    Most aftermarket car immobilisers disable the starter motor and the fuelpump. That's all mine does and it works a treat :)
     
  7. dark_knight

    dark_knight Registered User +

    +12VDC ECU power feed

    between pin7 (+B) and pin2 (BATT) on connector3, which one powers the ECU..? as in, which would disable the unit completely when disconnected..? i'm guessing pin7.
    secondly, would it be safe to cut power to the ECU when the engine is running..? presumably at mid- to high-revs..?
     
  8. dark_knight

    dark_knight Registered User +

    tried these two. engine stays running. didn't leave them disconnected long enough to know whether it would have sputtered and died.. so what's the best way around this..?
     
  9. pilgrim_fgau

    pilgrim_fgau Paid Member

    would this not cut the fuel too, making it possible to be running extremely lean for a short moment?

    All I am thinking is, I remember being told a while ago when someone needed to blast a stubbord bolt to pieces, they heated it with oxygen and acetylene until glowing red then turned of the acetylene and it pretty much disintegrated the bolt... same thing happening here maybe?
     
  10. dark_knight

    dark_knight Registered User +

    ignition trigger

    yes pilgrim_fgau, an ECU power cut may cause other problems -- leaning out and elevating cylinder temps to an unsafe level. so then, how do i cut ignition from the ecu pins..? is it pin3 (IGF) -- ignition feedback, or pin22 (IGT) -- ignition timing..?

    & what does the tale about the bolt have to do with this..? :)
     
  11. pilgrim_fgau

    pilgrim_fgau Paid Member

    yea kind of went off on a story there... sorry :) just highlighting the importance of not cutting the fuel off completely.. at it likes to make metal look like a icecream on a hot day :)
     
  12. dark_knight

    dark_knight Registered User +

    i get you pilgrim_fgau, but you still haven't helped address my quagmire.. :p ideas..?
     
  13. pilgrim_fgau

    pilgrim_fgau Paid Member

    honestly... I have no idea :p
     
  14. Paul_JJ

    Paul_JJ Registered User +

    Fuel pump as already mentioned the most popular part to disable with an aftermarket alarms. However I would also recommend to disable the main battery - until certain button pressed - no battery feed.
     
  15. dark_knight

    dark_knight Registered User +

    battery feed

    thanks Paul_JJ, but i want a trigger that when disabled even once the engine is running, will kill the car. the battery feed is a good idea, but once the engine is running then the alternator is powering the car, unless i disarm a circuit that controls the alternator/charging system as well.
    really trying to keep away from the fuel cut remedies.. hence the reason i'm looking at alternatives.. :/
     
  16. weeJohn

    weeJohn Paid Member

    The ignitor and injector triggers are both earths switching an already live feed at both these components. There is a common 12 volt feed to each injector and the coilpack 12 volts supply, thats the one you want to break to immobilise spark and fuel at the same time. If the car is in motion, if it is kept in gear and the clutch out, the engine will still provide vacuum for the servo and the pas pump will still be rotating so there will be brakes and steering assist still available.
     
    Last edited: Apr 6, 2012
  17. dark_knight

    dark_knight Registered User +

    thanks weeJohn. so what triggers am i looking at on the stock glanza ecu..? i think the relay i'll be using to switch this only has one switched side so hope i'll only need to immobilize one trigger.. :)
     
  18. Texx

    Texx Administrator

    I would cut the ground wire on the coil side of the EFI relay. It's a low load circuit and will take out both the fuel pump and ECU at the same time.
     
  19. dark_knight

    dark_knight Registered User +

    relay ground wire

    Texx, i doubt it but does this efi relay ground come all the way to the cabin (harness)..? i only but recently neatened up my engine bay harness with fresh tape and all so being a little picky not wanting to butcher all that up again.. :/ hehehe. i know.. being lazy.. :)
     
    Last edited: Apr 6, 2012
  20. Texx

    Texx Administrator

    IIRC the EFI relay is grounded behind the passenger side headlamp.

    Keeping the wiring in the cabin, I would cut the ground to the ECU, E1 possibly pin 24 of the 26 pin connector (would need to check the wiring diagram to be certain). Or the +12v switch feed to the ECU from the EFI relay, possibly pin 7 of the 12 pin connector (again would need to check to confirm).
     

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