jstck

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: http://www.quadesl.com/pdf/immoblizer.pdf

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.

18psi

iTrader: (76)

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)

Reverant

iTrader: (10)

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

jstck

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.

Braineack

iTrader: (62)

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

Kaffimonsen

Hey! Did installing a megasquirt solve this problem for you?
I got my megasquirt today which I bought to bypass what I thought was a faulty immobilizer on a 1996 1.6 MX-5. But installing it didn't seem to do anything for me. (Car still cranks but won't start) Did you manage to remove the immobilizer in yours or do you still have it in?
I was wondering if jumping those pinouts would solve the problem for me if the immobilizer controls anything without help from the ecm.
I also rock a Temic.

lsdlsd88

your not starting problem is not related to the immobilizer (with megasquirt).
and by the way, with stock ECU and a faulty or disconnected immo, the car will start anyway, run for 2 seconds and then cut out.

are you sure it's really a plug and play unit for your car/engine/year? your factory ecu was a B6HA?

jstck

Wow, this is a blast from the not-so-distant past.

On Megasquirt, the engine starts and runs just fine with or without the immobiliser unit connected. It would however sometimes start flashing the immobiliser light on the dash (don't remember quite what made it go off, something with running it a while or a few consecutive starts or something). Just unplugging the immobiliser fixed that just fine. There was no need to jump any cables, that wiring info was just a red herring. Also with the immobiliser out of the picture I can use a copied key (lacking the RFID chip) to start the car, since I only have one key for it and can keep that somewhere where I am unlikely to lose it.

jstck

Actually, Kaffimonsen, laying awake all night thinking about it there was one thing I had an issue with that might be what you're seeing. When I put the Megasquirt in (an MS3-Pro) in my 1997 1.8 would also crank but not start, since the fuel pump relay wasn't engaging.
The documentation I had on the ECU wiring said the fuel pump relay was a light green cable on pin 1U. However, pin 1U was light green with a red stripe (something I had not spotted earlier) and the fuel pump relay turned out to be right next to it on pin 1V (which was light green). So I just changed that pin in my homegrown adapter, and it started.
No idea why there is this difference in the wiring harness / ECU pinout, it may or may not have something to do with it having a factory immobiliser.

Kaffimonsen

Thank you for your quick reply! So you had to switch the pin on the ecu to get your car started after installing the megasquirt? I have the same unit as you do.
Do you still have the Documentation for the pinouts on the ecu?
Mine might be different though. it's a 1996 1.6
But thank you anyway. Now I have a lead for where to look to locate the problem.

lsdlsd88

what was your stock ECU part number?
1996 1.6 and 1.8 have quite a few differences!

Kaffimonsen

Not sure if it's the part nr. B6HA 18 881

lsdlsd88

yes so as I thought, your ecu pinout will be pretty much same as the early 1.6 115hp except,
4 inj outputs (like the 1.8)
CAM signal from CAS could be on pin 2F instead of 2G.

read about fuel pump control and ST-SIG fuse!!

Kaffimonsen

Sorry I didn't see your first post I was at work and on my phone. I thought it would be plug and play... I bought the corresponding MS to match my car... But it's not?
I just figured it would be a problem related to the immobiliser.
I had the car at the Mazda workshop where they tried to install an ecu from another car for me and they told me there was a communication error between the ecu and immobiliser. They couldn't find the error and they didn't want to spend time searching for it. So they asked me to take it back.
I had the car running fine until the battery went flat and I managed to reverse the poles while jumpstarting. After that the car cranks but won't start. I thought I burned the ecu or immobiliser...

jstck

I made a list somewhere of all the pins and wire colours but it is a bit messy, in Swedish, and mostly has references to the pin numbers of my "adapter board" (and wouldn't quite match your 1.6 anyway). It's all based on wiring diagrams randomly googled, I think this one was the main reference. I think it all matched that one, apart from the fact that I had an immobiliser (which I could just ignore and unplug once on MS, it turned out), and the fuel pump relay being on a different pin.

I wasn't using an MSPnP (plug&play) type unit, but a generic one with just a big bunch of cables that I then wired myself via an adapter board to a plug that fit the cars harness. So for me it was simple enough to just move the MS fuel pump signal to a different pin in the ECU/harness plug. I imagine doing the same thing for an MSPnP unit would be a bit more tricky, but you could just cut and splice the car harness to do that if you have the same wiring oddity as I do.

Kaffimonsen

https://www.diyautotune.com/product/megasquirtpnp-g2-mm9093-for-the-90-93-mazda-miata-manual-trans/ This is the one I bought. I read on DIYautotune that this is the one that would fit a europan 96.
It might be an entirely different problem though.
But it would be very convinient if it's just switching up a pin or two
The mechanic said that there's neither spark or fuel. That's why I thought it would be the immobiliser.
I found the wiring diagram for mine too but I'm not very profficient at reading wiring diagrams yet.
I'll have to look into it.

jstck

If you tried to jump it with the cables crossed, there's no end to what might have been burned. I'd go over everything else to make sure it still has power and does what it should (fusible links, fuses, relays, coil pack), make sure there is fuel pressure. If the immobiliser is wired the same way mine is, it isn't part of the problem. All it really does is tell the stock ECU "all is ok you may start" when it detects the right RFID key, and the Megasquirt will not be the least bit bothered by the lack of an immobiliser to talk to.

lsdlsd88

if they only swapped another used factory ECU of course it won't start, it's not matched with your immobilizer box...

you bought the right one, but note this FAQ on that site:

"almost" is the key word here.
in the previous post I wrote you the 2 basic differences that will allow it to start.

Althought, this is only ASSUMING that your car had an issue with either the ecu or the immo, but it's not a good assumption to make after a polarity inversion!

Savington

iTrader: (31)

Let's not have open discussion on how to defeat the immobilizer with a stock ECU, please. Hondas have that and all the myriad of theft issues that go along with it. I am perfectly OK with the fact that you cannot defeat the Mazda immobilizer without a standalone ECU.

Kaffimonsen

So the cam signal might be missplaced?

They changed the immobilizer and the stuff around the key too, and programmed new keys.

It was the mechanic who told me that everything seemed to be in working order except the ecu. And that there was some error with the communication between the ecu and immobiliser.

The car was at the workshop for over a month, they had a mechanic fault searching and trying different things on it whenever he had spare time.
He might have been an apprentice though.

Thank you so much for all the information, everything helps at this point.