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Old 10-24-2008, 08:42 AM   #1
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Default Standalone MS and factory immobilizer 99+ ?

Hi,

as usual - one more question to ask

When I go standalone I'd like to know what happens with my factory immobilizer? I don't know how often this is in your US cars - but for Germany all 99+ cars are equiped with this factory immobilizer unit. (Circuit from 99 wiring diagram attached)



I suppose I have to bridge it somehow, because I think it works like this - send a signal to the ECU - receive an answer - correct ECU - car stays running. (With an wrong answer - i.e. other ECU it stalls the car after 3 sec.)

Any experience with this?

Thanks
Greets

Sven
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Old 10-24-2008, 08:44 AM   #2
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Sorry I don't have an answer to your question, but I do have a question for you...What exactly does this feature accomplish? The car will start only with the correct ECU if I'm understanding you correctly.
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Old 10-24-2008, 09:01 AM   #3
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It is even more than that - it's the combination of three things - the key, the immobilizer unit and the ecu. All three things have to belong together. There is a transponder inside the key, which is read by a coil next to the lock, the immobilizer reads this transponder and the "whatever" of the ECU. It is a mayor pita to learn a new key to the existing ECU or the other way round.

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Old 10-24-2008, 09:02 AM   #4
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Interesting, I don't think the NB's here have anything like that. Must have high auto theft rates in Germany? Sorry for the thread jack, somebody help this guy out.
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Old 10-24-2008, 09:25 AM   #5
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Quote:
Originally Posted by KPLAFIN View Post
Interesting, I don't think the NB's here have anything like that. Must have high auto theft rates in Germany? Sorry for the thread jack, somebody help this guy out.
Well Eastern Europe is not too far away, so yes the theft rates are quite high...

And yes - please help this guy out...
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Old 10-24-2008, 12:14 PM   #6
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There is nothing magical about the immobilizer. Since you are removing the stock ECU and installing a Megasquirt, you are defeating the authority of the stock immobilizer. The Megasquirt will continue driving the injectors and the ignition system regardless of what the immobilizer does.

My US-spec '99 manual does not have this circuit, so my apologies if I'm a bit slow at understanding. I assume that the device marked "SPULE" is the coil around the lock which reads the key. Given this, the immobilizer has only two other I/O ports. One goes to the instrument cluster, which I presume simply illuminates a lamp that says "SECURITY" (or whatever the correct translation into German would be) and the other line goes to the ECU, presumably to disable it.

Thus, if the ECU is not there, then the immobilizer has no teeth. It cannot shut down a Megasquirt, as the two devices do not speak the same language.
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Old 10-24-2008, 12:38 PM   #7
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I can't see a wiring diagram in your post, but I'm at work so it's possible it's blocked for me ATM.

Many early immobilizer systems (mid-late 90s) were just between the key and the ECU. If the ECU doesn't get the right code, it doesn't supply fuel, spark, etc. In that case, since the immobilization is done by the ECU, then going standalone would remove the immobilizing function and it wouldn't be an issue. [EDIT: So yeah, what Joe already said.] The point of these is simply to prevent theft, and really, what thief tries to replace a car's ECU before stealing it? Ford systems were of this type, so based on the close relationship between Ford and Mazda, I'm guessing yours is this way.

I've heard that some of the newfangled systems are in a separate box from the ECU, and require signals from both the key and the ECU. From what little I've read on the subject, these are basically relay boxes that don't allow power to the starter/fuel pump/ignition circuit(s) unless they receive the right codes from multiple sources. If this is the case, you'll have to either A) find the box and bypass the relays, or B) leave the stock ECU in for the sole purpose of sending the code to it while the MS does everything else.
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Old 10-24-2008, 02:11 PM   #8
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Hi Joe, your German gets along nicely.

I think it is like Scott assumed last - the ECU cuts the power supply to the Fuel pump, ECU etc.

I think the ports called J & L in the circuit are a kind of power switch to the main relais. Could this be possible?

Thanks
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Old 10-25-2008, 02:37 AM   #9
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Quote:
Originally Posted by Zaphod View Post
Hi Joe, your German gets along nicely.
My German is terrible, but the schematic symbol for a coil of wire is the same in every language.

Quote:
I think it is like Scott assumed last - the ECU cuts the power supply to the Fuel pump, ECU etc.
Yes, it appears that the Immobilizer merely sends a signal to the ECU commanding it not to turn on (or perhaps permitting it to turn on when authorized by the key). In either case, without the ECU in place, this signal is meaningless.

Quote:
I think the ports called J & L in the circuit are a kind of power switch to the main relais. Could this be possible?
Let me think about that...

Both of those circuits are present in all Miatas. The one marked (J) is active at all times, and supplies power to a number of non-critical devices in the vehicle, such as the radio (to retain settings), the gauge cluster, the interior lamps, and so on.

The one marked (L) is the primary power feed to the ECU, the ignition coils, and the control coil of the main relay. If the 15A "ENGINE" fuse were opened, then the engine would not run. I suppose it is theoretically possible that the immobilizer could intentionally blow this fuse to completely disable the vehicle (by shorting it to ground through a relay) however I doubt that Mazda would design it in such a way. I suspect that it is connected only so that the Immobilizer knows when to communicate with the ECU.

For anyone else who cares, here is the service manual for the immobilizer: http://quadesl.com/pdf/immoblizer.pdf
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Old 10-25-2008, 03:59 AM   #10
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O.K. I will give it a try and see, what happens.

I don't think it is intended to blow a fuse - I just thought it would cut the power to the main relay or such.

We'll see.

Danke Joe
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Old 10-25-2008, 01:03 PM   #11
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Quote:
Originally Posted by Zaphod
I don't think it is intended to blow a fuse - I just thought it would cut the power to the main relay or such.
Yes, I don't think that they actually would cause it to blow the fuse, I was just pointing that out as an interesting possibility.

It cannot disable the Main Relay, as that is not controlled by the ECU or the Immobilizer. Here is a drawing of the main relay circuit in which I've removed all the non-relevant information, and I think this is the same for all cars (both Euro and US), whether or not they have the immobilizer:



You can see that the key switch provides power directly to the main relay coil whenever the key is on. The immobilizer is not installed in such a way that it could interrupt this path.


Quote:
Danke Joe
Bitte.
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