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Old 03-30-2016, 08:31 AM   #1
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Default Removing immobiliser with stock ECU

I just realised my european 1997 NA MX5 has an immobiliser in it. A Temic unit (picture attached), from what I understand the same one as is found in later NB's. I'm installing a megasquirt in a month or two, but I would like to be rid of the immobiliser even on the stock ECU if possible. I expect to have to go back and forth between ECU's a couple times while sorting out various "do you know what the **** you're doing" issues, and it's just one more hassle.

What little info I found on pinouts and such was from here:

I tried unplugging it and jumping the two pins in the connector to feed power to the ignition coil pack (D and L in the diagram, via a fuse), but the car won't start. That would mean that it's not just the immobiliser itself preventing a start, the ECU (PCM) also doesn't want to run unless the immobiliser says it's ok and the rfid in the keys match and whatnot. Which makes sense, without that the immobiliser would be fairly easily defeated.

From what I understand US Miatas didn't get an immobiliser until the NB, so not all stock NA8 ECU's should require one. Is it possible/feasible to make my ECU not care about the immobiliser?
Alternatively, is it possible to run the car on an aftermarket ECU with the immobiliser (i.e. does the immobiliser check the serial of the ECU or something)?

Once I go to the Megasquirt, is this a correct&reasonable way to do it (jumping those two pins)? If I were to do that permanently I'd splice the wires at the immobiliser connector (and unplug it). Maybe install my own "kill switch" like a proper ricer. Might also use the leftover dashboard light for some other function.
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Removing immobiliser with stock ECU-immobiliser.jpg  
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Old 03-30-2016, 08:59 AM   #2
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once you go ms, you don't need it at all, and you shouldn't even need to remove it. it just wont be used.
but while you're on stock ecu, you wont be able to get around it (the ecu and immob interact and it's not a matter of jumping wires)
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Old 03-30-2016, 09:30 AM   #3
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You can't remove the immobilizer with the stock ECU.

The immobilizer on the NA8 and NB1 don't cut the ignition coils or anything, the stock ECU does.

The car will run fine with the MS and the immobilizer still in place but you may get an immo light after about 2 minutes
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Old 03-30-2016, 04:14 PM   #4
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Ah, so the stuff in that PDF about the immobiliser de-powering the ignition coil is not correct (for my particular car)? Good to know. Once I'm set with the MS, if it lights up the warning light I'll just unplug the immobiliser.
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Old 03-30-2016, 04:27 PM   #5
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Yeah the ecu just won't run the car if it doesn't get the correct signal back from it. Remove the ecu and it's not a problem, just deal with th the light, unplugging unit will probably work
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