best way to disable the car electronically

dark_knight

Member +
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..?
 
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Texx

Super Moderator
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.
 

dark_knight

Member +
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..?
 

Franza1

Supermoderator & Area Reps Manager
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.
 

Franza1

Supermoderator & Area Reps Manager
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
 
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Texx

Super Moderator
The coil is grounded by the igniter, the igniter switches the coil OFF based on the signal that comes from the ECU. Without an IGT signal from the ECU the spark will not occur.

Similarly, the fuel pump relay is grounded by the ECU. The ECU needs to first identify the STA signal from the ignition switch and then detect a Ne engine speed signal from the distributor before it'll ground the fuel pump relay.


Without the ECU powered ON, the fuel pump will remain OFF, the fuel injectors will not fire and the spark from the ignition coil will not occur.
 

dark_knight

Member +
ignition timing trigger

so are you both telling me that i can resolve this by using the IGT as a cut-out trigger..? meaning there will be no spark and no injector duty..?
 

Texx

Super Moderator
Personally I would power down the ECU rather than cut the IGT signal. If you cut the IGT signal the ECU will store code 14, however it will also cut the fuel injector pulse after it does not receive the IGF signal from the igniter at least 8 times in succession. Basically if the ECU does not receive the signal that confirms the spark has occurred it'll shut the injectors off.

Again powering OFF the ECU is a much better solution.
 

dark_knight

Member +
safety/security concerns

alright Texx, that sounds like a very logical reason to want to pick that route. i think it's a worthy consideration given that this is not an every-time kinda cutout scenario. but again, having my ecu re-learning driving habits is a small price to pay if you ask me..

also, admins here; could you please advise if this is a thread we can keep alive or purge given that it revolves around car security.. same way sharing the ignition barrel pin-outs is not exactly public information..?
 

Texx

Super Moderator
but again, having my ecu re-learning driving habits is a small price to pay if you ask me..

As long as the ECU does NOT lose it's ground connection and the +12v feed from the 15a EFI fuse remains in place at pin 2 (BATT) of the 12 pin connector, the ECU will retain it's memory and no relearning process will be required. What your looking to cut is the switched +12v from the EFI relay that feeds the ECU at pins 1 and 7 of the 12 pin connector. Cutting +12v to both pin 1 and 7 of the 12 pin connector is no different to switching the ignition OFF.
 

dark_knight

Member +
missing wire at pin1 on the 12-pin plug

alright Texx, but if you read my earlier posts, i tried pin7 (+B) switched batter power (12v) on conn3 and engine didn't cut out, or does it keep running only to die a few seconds later..? ..coz i didn't wait longer than 5 seconds iirc. also, my 12-pin plug (conn3) has nothing at pin1 (no wire), so i could only try pin7.
 
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Texx

Super Moderator
If you pull the EFI relay when the engine is running, does the engine cut out straight away?
 

dark_knight

Member +
efi relay

i haven't tried that Texx. maybe i give it a go in a couple of hours (my morning) and report back as it is almost 23h00 here and i'm looking at getting some shut-eye.. :)
 

dark_knight

Member +
ecu relay trigger

and yes, pulling out the ECU relay prevents the engine from cranking to life and if running already, it cuts out immediately. question is, does the relay coil-side wire come into the cabin (to the ECU) via the cabin harness..? it would be easier to tap this as a trigger don't you think..?
 

Texx

Super Moderator
and yes, pulling out the ECU relay prevents the engine from cranking to life and if running already, it cuts out immediately.

This leads me to believe there was something amiss when you cut the +B wire at pin 7 of the 12 pin connector.

What you'll need to do is pull the EFI relay again and also the 12 pin ECU connector, then with the ignition OFF using a meter check for continuity between the relay terminals in the fuse box and the terminals of the 12 pin ECU connector. You should identify the switch output terminal of the relay that has continuity with pin 7 of the 12 pin ECU connector. Once you have identified the switched +12v output of the relay you can then proceed to find any other terminals in the 12 pin ECU connector that also have continuity with the switched output of the EFI relay, there must be more than just pin 7 otherwise the ECU would have shut down when you previously cut that wire, other than that it wasn't the wire at pin 7 that you cut.

You may see continuity at pin 4 which is the switched ground (FC) for the coil side of the fuel pump relay, however the reading should show the resistance of the relay, this wire should be left untouched.
 

dark_knight

Member +
efi relay non-existent

thanks Texx. what i did was trace the ECU relay coil-side ground wire into the cabin and testing that as a trigger to disable the ECU -- we were/are in agreement that this is a safe way to do it right, with little risk to the engine, right..?
i don't have an EFI relay in my engine bay fuse box.. or are we talking of different things..? i'm actually at the car now so can trace/check for continuity like you said between the relay and 12-pin plug at the ecu.
 

Texx

Super Moderator
thanks Texxi don't have an EFI relay in my engine bay fuse box..

EFI or ECU relay, it's the same thing mate. :)


TBH it doesn't really matter whether you cut the switched +12v from the relay to the ECU or you switch off the relay by cutting either the +12v or ground to the coil side, it'll serve the same purpose. Just ensure you don't cut the ground to the ECU or the +12v at the BATT terminal of the 12 pin connector and all will be good.

By doing the above you will simply be replicating the what the ignition switch does when it's in the OFF position, so there should be no concerns.
 

dark_knight

Member +
relay

ahh.. good one. glad to have got that out of the way.. :D
let me test/trace the connector wires you mentioned. will report back shortly..
 

dark_knight

Member +
thanks

good one. thanks Texx. you've been instrumental in this despite not having a glanza. i suspect you have a GT..? :) all the same, you truly have a very good understanding of the wiring concepts here.. and that came in very handy and helpful.. :D
repped..
 
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