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  1. #1
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    Question best way to disable the car electronically

    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)

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    Quote Originally Posted by dark_knight View Post
    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)
    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.

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    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

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    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.. :/

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    Question 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 by dark_knight; 06-04-2012 at 11:48 AM.

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    Super Moderator dac69er's Avatar
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    Most aftermarket car immobilisers disable the starter motor and the fuelpump. That's all mine does and it works a treat
    198bhp and 198lbft and 15.07 quarter mile at santa pod. 860kg with 1/4 of a tank of petrol!

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    Question +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..?

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    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..?

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    Quote Originally Posted by dark_knight View Post
    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..?
    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?

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    Question 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..?

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    Quote Originally Posted by dark_knight View Post
    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..?
    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

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

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    Quote Originally Posted by dark_knight View Post
    i get you pilgrim_fgau, but you still haven't helped address my quagmire.. ideas..?
    honestly... I have no idea

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    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.

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    Cool 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.. :/

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    Super Moderator weeJohn's Avatar
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    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 by weeJohn; 06-04-2012 at 06:24 PM.
    243 bhp, 210 ft/lbs of torque, 4 wheels to put it through

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    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..

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    Administrator Texx's Avatar
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    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.

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    Unhappy 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 by dark_knight; 06-04-2012 at 07:52 PM. Reason: added a link :)

  20. #20
    Administrator Texx's Avatar
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    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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    Exclamation ecu ground

    i tried the +12vdc switched feed (pin7 on conn3) Texx but engine didn't go out. i have to admit i didn't wait longer than 5 seconds as i was afraid something may be going wrong and may fry my ecu/engine but yeah.. i will try the ground, although there's three of them (pin13, pin24 & pin26 on conn1) so does that mean i take all out or just E1..?
    Last edited by dark_knight; 06-04-2012 at 08:07 PM. Reason: corrected my statement on the grounds

  22. #22
    Administrator Texx's Avatar
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    The downside to cutting the ECU ground is that it'll reset the ECU every time and it'll spend the next few hundred miles relearning it's parameters.

    If you pull the 12 pin connector from the ECU and switch the ignition ON, you should get +12v at pin 1 (+B1) and 7 (+B). If you cut both of these wires that should kill the ECU, taking out both the fuel pump and ignition signal at the same time. Although I'm not 100% on pin 1 being +B1 as it's not on the circuit diagram, you'll have to check for zero resistance (ignition OFF) between pin 1 and 7 with a meter to confirm.

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    Lightbulb efi relay

    i was thinking the same thing until you mentioned it, about the ecu re-learning driving style each time i cut-out..
    looks like that efi relay ground is the most viable option -- i'm assuming this will take out ignition and fueling..? can you confirm..?

  24. #24
    Supermoderator & Area Reps Manager Franza1's Avatar
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    best thing to do is to cut power to the coil, car won't run and won't be a danger as overfueling for a split second till the spark dies will not cause any problems major or small. the PAS and Breaks will still work on.

  25. #25
    Supermoderator & Area Reps Manager Franza1's Avatar
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    Injectors will not keep running long enough to cause any problems what so ever.

    Scenario : Car won't start as Coil is disables, no thief will bother staying around for the 20 or so mins it will take to flood the engine.
    Scenario 2 : car cut while driving, thief/driver panics trys to re-start the car, pushes in clutch car dies, trys to bump causes the car to slow and stop, thief/driver legs it. all happening in the space of 2 mins
    Last edited by Franza1; 06-04-2012 at 08:34 PM.

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