Mx5 Mk2 starts sometimes

My 1999 Mx5 Mk2 failed to start on a trip, in spite of the efforts of two recovery mechanics, and had to be trucked home. Kudos to Lancaster Insurance.

There was no warning other than that, on only one occasion a few weeks before, I had to turn the key three or four times to start: unheard of for a vehicle that has always leapt into life at the first turn. Since then an excellent local old car specialist – but with limited experience of MX5s – has checked the usual things: ignition, fuel pump etc. He has replaced the air flow meter and camshaft position sensor which has improved things. It now starts sometimes and runs and drives perfectly when it does. No fault code from diagnostics. No engine warning light. Battery fairly new and fully charged. Both keys tried.

From research, he suspects the immobiliser but not the ECU. He has inspected both the immobiliser and ECU and can find no damage, corrosion, or dry connections. He is surprised that the immobiliser on this Japanese car is from Lucas: significant perhaps? I haven’t worked on the car myself as eleven years of completely trouble-free motoring with it means I know next to nothing about what happens under the bonnet, although I am pretty used to dealing with suspension arms and rust etc of course.

Before I lay out some folding money on Ebay for an ECU, immobiliser, keys and barrel set, I’m wondering whether there is any way to pinpoint the problem?

Wouldn’t crank or wouldn’t fire? Any fault codes stored?

Thanks for the interest Robbie. Cranks fine but not firing. No fault codes stored.

Might be worth checking/changing the crank position sensor.

Assuming that a ‘crank position sensor’ is the same thing as a camshaft sensor then yep! It’s been replaced.

Nope, cam sensor is on the cam cover, crank sensor is next to the bottom pulley.

Agree, crank sensor most likely. I had similar fault develop which went away just after adjusting gap between sensor and pulley, although never figured why it suddenly needed adjusting as had obviously been in same position for years.

Thanks to both! I’ve asked the guy who’s working on the car to check and will report back.

The crank sensor has now been checked and reset, but with no improvement. Focus now seems to be firmly on the immobiliser.

Having ruled out the air flow meter, crank sensor, fuel pump and other obvious causes, the focus is now on the immobiliser.

This vehicle has a light on top of the dash board that flashes continuously when the car is not in use, which I take to be the security light, although the manual shows this as being part of the instrument cluster, not on top of the dashboard.

That light is not going off when the engine is cranked, which is the reason for thinking this is an immobiliser problem.

On the rare occasions the car does start, it runs for a while and then stops dead.

We have tried fitting an immobiliser simulator which is intended to bypass the immobiliser. The security light now does go out when the engine is cranked, but the red ‘key not recognised’ light come on and stays on which it didn’t do before. The car doesn’t start at all − ever.

The simulator supplier has no knowledge of a constantly winking light on top of the dash board and suspects that this may be an aftermarket modification. In that case there may be another immobiliser that is causing the problem.

I will be very, very grateful once again if anyone can tell me if:

  1. this kind of security light on top of the dashboard was fitted to MK2s as standard.
  2. anyone has any suggestions that might stop me climbing up the wall.

Sounds like an aftermarket light to me. Can you post a photo of it?

Thanks. Can do, but the car is at a garage at the moment so not immediately

I’m sure you’ve checked this but just in case, I had a similar issue with my Eunos just couldn’t fathom it, it would randomly not start. It turned out to be the immobiliser detection loop which should have been around the barrel had dropped down into the steering column cover. Moving it back around the barrel solved the issue.

Thanks grumpybadger. As the guy who is working no the car (this job is a bit beyond my pay grade) has had the coil out for testing I assume that it went back in the right place. But we all make mistake re-assembling so I’ll mention it.

(comment replaced after accidental deletion by author − sorry)

The flashing security light is situated on top of the dash board close to the LH end of the windscreen de-mist opening as shown below. Cannot show in situ as dash board presently dismantled. It flashes twice a second − with a just audible click − when the car is not in use, but I can’t remember whether it normally goes off when the key is inserted or when the engine starts.
Security Light Location

We are still trying to solve this problem.

The two wires from the flashing led on the dashboard (see above) are connected into wires that run between the loom and the key barrel. Disconnecting the led does not help but the clicking noise when the led flashes has stopped.

We’ve tried an emulator on the OEM immobiliser. This causes the ‘key not recognised’ light to come on; an additional problem. It has been removed and key now recognised.

Although the fuel pump primes when the key is cranked, there is no spark.

The mechanic who is working on the car for me suspects that there is an aftermarket immobiliser somewhere and has got in behind the instrument panel and the fascia panels above and below the steering column, but can see no sign of another immobilizer.

He is reluctant to dismantle the whole of the fascia without a very good reason but it is extremely difficult to trace cables in this area. He is very experienced and respected where keeping elderly vehicles safely on the road is concerned, but not an MX5 specialist; hence the questions below.

Please can anyone throw any light on what is in the photo below showing the rear driver’s side of the engine compartment:

  1. a slit in the grey booting in the bulkhead to accommodate a cable which suggests some kind of modification.
  2. this cable goes to the narrow black box on the extreme left of the photo between the fuse box and the wing. Does anyone know what this unit is or is it likely to be a modification?
  3. there is a Lucas socket and yellow relay near the fuse box (the immobilizer is also Lucas; coincidence?). Swapping out the relay does not help. This also looks like a modification of some kind but we don’t know what it is?

I will be very grateful to anyone for help as this has turned into a mega problem as we are running out of ideas.

1 and 3 are not factory fit. Shouldn’t be too difficult to follow the wires to find out what they are connected to. From memory, there should be relays under the black cover (2). Don’t link the Lucas relay to the Lucas Immobiliser (assuming that is factory). The relay looks a bit like the one for accessory front fog lamps, if a UK accessory.

Very many thanks Robbie, that helps to move things on.
Work on this only progressing now when there is downtime now, but we will investigate that box (2). Trouble is that the front of the M2’s cabin is an easier place to trace cables for a slim, bright, twelve-year old than an elderly six-foot-something weighing the best part of 20 stone, or a stiff near octogenarian. No bright kid available at any price unfortunately!
Surely there must be some way to get a vehicle with a possibly dodgy immobilizer started for diagnostic purposes, or is that a secret only known to Mazda agents? And do they have a way of getting at fault codes that don’t appear with the flash codes?

How are the “flash codes” being read currently? Via the diagnostic socket under the bonnet?

Using a fault code LED under the bonnet; nothing stored. I understand that there is also a socket but the available fault code reader (a proper professional one) won’t connect to it. Might this make a difference if we could, and is an adaptor a possibility do you know?