NA starting problems - immobiliser?

Purfler · Postby **Purfler** » Thu Jun 25, 2020 12:28 pm

Hi all,

I would be very grateful for some advice on a problem that has just arisen with my car:

The car:

1993 NA6 LE (as with all these it is fitted with an alarm which incorporates an immobiliser. I think this is significant)

The problem:

It cranks but will not start. Yesterday it would occassionally fire and run for 10-20 seconds then die.

What I’ve done:

I have the Haynes manual and have followed that.

1. I can find no vacuum leaks in the intake side.

2. There is spark at the plugs.

3. I have removed and tested both the EFI relay and the circuit opening relay in accordance with the Haynes manual. They both test OK. There is power to the EFI relay and both “click” when the ignition is turned to on (with a jumper between GND and FP in the diagnostics box).

4. The EFI fuse is ok (I also swapped it with a known good one)

5. There is no voltage at the red/blue wire in the connector to the fuel pump.

6. I have removed the fuel pump and connected it to 12v. It operates.

My guess:

The immobiliser has failed. For a while it has made the odd clicking or buzzing sound when I turn the ignition on – possibly a relay in it failing?

As I said at the top, I would be grateful for any thoughts from the brains trust.

Regards and thanks,

Tim

93_Clubman · Postby **93_Clubman** » Thu Jun 25, 2020 6:13 pm

No Start Guide: http://wiki.miata.net/tiki-index.php?pa ... tart+Guide

Purfler · Postby **Purfler** » Fri Jun 26, 2020 10:02 am

Thanks, I'll work through it.

Tim

93_Clubman · Postby **93_Clubman** » Fri Jun 26, 2020 1:10 pm

Had a bit more time & came up with the following thoughts:
NA starting problems - immobiliser?
The car:
1993 NA6 LE (as with all these it is fitted with an alarm which incorporates an immobiliser. I think this is significant).
[might be wrong but don't think the 1993 NA6 LE was fitted with an immobiliser from the factory so this could be aftermarket which are a curse]
The problem that has just arisen:
It cranks but will not start. Yesterday it would occasionally fire and run for 10-20 seconds then die.
[generally faulty immobilisers won't allow any firing or starting]
What I’ve done:
I have the Haynes manual and have followed that.
1. I can find no vacuum leaks in the intake side.
2. There is spark at the plugs.
3. I have removed and tested both the EFI relay and the circuit opening relay in accordance with the Haynes manual. They both test OK. There is power to the EFI relay and both “click” when the ignition is turned to on (with a jumper between GND and FP in the diagnostics box).
4. The EFI fuse is ok (I also swapped it with a known good one)
5. There is no voltage at the red/blue wire in the connector to the fuel pump.
[perhaps the so called 'blackwire' problem? See: viewtopic.php?f=55&t=46425
&
viewtopic.php?style=3&f=55&t=70835
&
manga_blue post ref possible shorting of connectors on fuel pump due to a build-up of iron filing type material on the fuel pump body]
6. I have removed the fuel pump and connected it to 12v. It operates.
[but are the spark plugs wet, ie actually getting fuel?]
My guess:
The immobiliser has failed. For a while it has made the odd clicking or buzzing sound when I turn the ignition on – possibly a relay in it failing?
[if it's definitely the immobiliser making a noise which it previously didn't then it could be the immobiliser in which case bypass it although usually easier said than done]

Purfler · Postby **Purfler** » Fri Jun 26, 2020 1:44 pm

This is going to sound stupid (or more stupid than usual). How do I know if the car has a CEL? Coming to do the checks I realise I have no memory of ever seeing one. The Owners Manual, original to the car, makes no mention of it. This video says some NA's did not have one (mine is Aus delivered) and shows using LEDs to replicate a CEL.

I will see if I can make up an LED CEL as shown in the video anyway, but it is frustrating no knowing if there is one that is not coming on (meaning a bunch possibilities) or there isn't one to come on.

As always, thanks.

Tim

Purfler · Postby **Purfler** » Fri Jun 26, 2020 2:22 pm

Many thanks 93_Clubman. I made up the LED and got a code of 1 flash - ignition pulse. I will work through the tests for ignition, but I'm strongly inclined to think it is the immobiliser. It is aftermarket judging by the installation, done as part of the LE package. I have been dreading this as I've read of others having the same problem. I also have a memory that there is an auto electrician in Sydney who is an MX5 person - and who will come to you. I hope I'm not dreaming this and can track him down, I'm not keen, or confident, in pursuing this too far myself.

Thanks again,

Tim

bruce · Postby **bruce** » Fri Jun 26, 2020 3:55 pm

No NA from factory had an immobiliser fitted (not even central locking, they were a very basic car). They were all done at a Dealer level or after purchase.
LE package was purely all the trim items from factory.

Purfler · Postby **Purfler** » Sat Jun 27, 2020 11:50 am

Sanity check time

The photo is one of the units in the alarm/immobiliser. I'm pretty convinced one of the big relays has carked it (the pcb seems to be adhered to the back of the case so at the moment I cannot get to the pins to test the relays. I don't want to force it apart and beak the board). The HG4119 relays seem to be available. Should I see if it can be repaired?

Thanks in advance.

Tim

https://photos.app.goo.gl/TaX7vw3KaTZeLvddA

93_Clubman · Postby **93_Clubman** » Sat Jun 27, 2020 12:17 pm

Purfler wrote:fitted with an alarm which incorporates an immobiliser.
It cranks but will not start. Yesterday it would occassionally fire and run for 10-20 seconds then die.
There is spark at the plugs.

Interesting that you have spark as would have thought faulty immobiliser would have suppressed this, but may be it suppresses fuel. Are the spark plugs wet, ie getting fuel?

Purfler wrote:How do I know if the car has a CEL?

ADM NA6 didn't have a CEL.

Purfler wrote:made up the LED and got a code of 1 flash - ignition pulse.

If you haven't already, it would be prudent to clear the stored fault codes in the ECU in case this is an old code. Just disconnect the battery & press the brake pedal a few times to clear codes, then check for fault code again to confirm.

Purfler wrote:have a memory that there is an auto electrician in Sydney who is an MX5 person - and who will come to you.

Not immediately coming to mind.

Purfler wrote:pretty convinced one of the big relays has carked it (the pcb seems to be adhered to the back of the case so at the moment ... don't want to force it apart and break the board). The HG4119 relays seem to be available. Should I see if it can be repaired?

You could, but get a quote in writing first. Personally, if you're going to pay an electrician to do any work then I would pay them to remove the immobiliser so the problem doesn't recur, as the immobiliser was a dealer or previous owner addition, & not from the factory as a part of the 1993 NA6 LE package. Investing in 27 year old electrics of unknown quality that have been subject to kms of vibration & bumps isn't something I'd do.

Purfler · Postby **Purfler** » Sat Jun 27, 2020 12:39 pm

Thanks very much again, if you were in Sydney I'd buy you a drink :beer:

The best course is to have it replaced with a modern unit. It incorporates central locking and as at some point in the car's life the ignition switch was changed (I guess) the keys are a bit of a mess.

I no longer rely on it for work (being ancient and on leave pending retirement) so there's no great hurry to get it back on the road, other than I'd like to go on a Datsun Sports Owners Association run next weekend. I cannot use my 2000 Sports as the chassis, body shell and engine block are trapped in Qld (it is long and bizarre story) so they let me use the MX5 :-)

I think I'll concentrate on bypassing the immobiliser for the fuel pump as an interim measure.

Thanks,

Tim

93_Clubman · Postby **93_Clubman** » Sat Jun 27, 2020 12:51 pm

No probs - hope you find easy resolution.

Purfler wrote:best course is to have it replaced with a modern unit.

Perhaps easier said than done, as my understanding is these units try to be unpredictable to thieves, so PnP swap unlikely.

Purfler wrote:think I'll concentrate on bypassing the immobiliser for the fuel pump as an interim measure.

Yeah, agree best short to medium, & perhaps long term, solution depending on your/the circumstances.

bruce · Postby **bruce** » Sat Jun 27, 2020 1:47 pm

Yes, best to pay a competent auto sparky to remove the unit and restore to factory. Best long term peace of mind.

Purfler · Postby **Purfler** » Sat Jun 27, 2020 1:58 pm

Further update for anyone interested.

Got the PCB out, the big relays seem OK. Found another unit with two relays that I didn't know about, which are more in the area I heard the odd noise. One of the relays seems not to be working, but I caused a short in testing (dumb!) and damaged the pcb - which I have repaired but may have stuffed something. This relay unit seems to control power supply to the one I first took out. If I have buggered it I have managed to make the situation worse. Ah well, live and learn.

I wasn't expecting to be able to find a plug an play replacement, I was expecting pain.

Tim

Ps - Just put it back together, yes, I've stuffed something. Engine cranks but does not fire (as before) but both indicators are constantly on. Time for the amateur to leave it alone and get someone who actually knows what they are doing. Any suggestions? I'm in the Ryde area in Sydney. I might ask on the Facebook group as well.

bruce · Postby **bruce** » Sat Jun 27, 2020 3:28 pm

Can't recommend anyone (as I'm in Melb) but you'd need a mobile sparky to come visit you (as tows are expensive unless you have some sort of tow coverage?)

93_Clubman · Postby **93_Clubman** » Sat Jun 27, 2020 5:15 pm

Similarly, can't recommend anyone. If you've got the time perhaps remove it yourself - just make sure you make notes & diagrams, & take pics before & after removal so you understand how the immobiliser intercepts & modifies the factory wiring. Then reinstate the factory wiring. Btw, if you haven't already, then remove the seat/s if you've got to work under the dash - your back will thank you!