Well, that was fun...

[Nevyn72]

As the sensors get older microscopic cracks form within the structure (due to heat cycling and vibrations, similar to metal fatigue) and when the cracks open can cause a break in the continuity of the internal circuits. Hence an interrupted signal chain to the ECU.

During normal driving the amount of heat soak is less than during a period of enthusiastic driving such as you describe.
This heat soak is sufficient to cause the cracks to open a little more (due to thermal expansion) and interfere with the signal and hence ignition control. This is what causes the misfire...

When you stop it doesn't take long for the sensor (not the whole engine necessarily) to cool enough for the cracks to close enough for normal operation.

Eventually the sensor will degrade enough that even normal operating temperatures, initially in summer, then all the time, will have the same symptoms.

The only real question is which sensor is it?... the Cam or Crank?

Then Murphy or his mate O'toole show up with a dodgy connector or wire...

[greenMachine]

I remember Magpie had CAS issues, and replaced the sensor with a Haltech product. Between that and using a potted connector he resolved an ongoing issue. That was justified in a racecar, not sure that our road cars require going to that length. Even it were, that sensor has disappeared from Haltech's website, probably available elsewhere though.

[Red_Bullet]

The CAS is easy to change on an NB2, it's easily accessible. Right at the front of the engine if I recall correctly on the intake camshaft. It's been a while since I looked, I sold my NB-2 a couple of years ago. The crank sensor I'd imagine would be more fiddly.

[Magpie]

The CAS is easy to change on an NB2, it's easily accessible. Right at the front of the engine if I recall correctly on the intake camshaft. It's been a while since I looked, I sold my NB-2 a couple of years ago. The crank sensor I'd imagine would be more fiddly.

The issue is not the sensor rather the plug itself. Test this by using a cable tie to pull both parts of the plug into each other and see if the problem is fixed.

FE76D0BD-9C36-44DD-A951-828880FB62FE.jpeg

The Haltech cherry red sensor is a simple Hall effect and can be purchased at most motorsport places.

[Rocky]

I have just had a look at the CAS - it looks a bit different to the picture above - and checked all the connectors, which seemed tight.
I phoned the Dealer and asked that they add both Sensors to the extensive list of parts to be replaced. Hasn't had a Dealer service in 20 years so I am going for broke (going broke?)

[Rocky]

MX5 in to the Dealer this am.
I was getting fobbed-off by the "Service Manager" on the phone. She had no intention of allowing me to speak with a mechanic so I went straight in to the Workshop this morning and asked to speak with the Workshop Manager or a senior Mechanic.
I spoke at length with the Workshop Foreman who was on the same wavelength as you guys and myself. He asked if he could take it for a test drive up Mt Archer and see if he could replicate the symptoms with some diagnostics attached, and of course that is what I want. At least Mt Archer is a few minutes up the road from where I live whereas Mt Morgan is 45 minutes away.
I asked that if the brake pads need replacing, they replace them with OE not the crap that put black dust all over the wheels.
Mt Archer should be a good test as it is a similar distance to the Mount although not as twisty. The problem however is that I have done 7 trips up the Mt Morgan Range this year and the problem developed only twice. Intermittent problems!!!
We will see what I have to report this arvo when I get it back.

[bruce]

How did it all go?

[Rocky]

OK, got it back at close of business today. Been in there since Wednesday am. Said problems obtaining some parts - Fuel Filter & spark plugs.
Service not yet completed as they need to order a Timing belt and consequently a Cam Cover gasket (if I understood them correctly)
Job was done as a 120,000klm Service plus whatever replacement items deemed necessary plus the "diagnostic" on the problem with engine stall.
First off, the Foreman took it for a run up Mt Archer and replicated the problem so immediately replaced the Cam & Crank sensors that I had told them to order based on the Forum's advice. Problem appears to be fixed.
Replaced Fuel filter, Air filter, Spark plugs, Drive belt, Power steering belt, and did the Oil change and filter.
Brake pads were good and tyres didn't need rotation.
Cost to this point $1810. Comprised of $855. parts & $716. Labour. $74. Sundries & $164. GST.
Unfortunately it is too old to put on the diagnostic machine.

The Mazda 6 will be next for the Major service and new Cam & Crank sensors as it has exactly the same problem as the MX5.

[93_Clubman]

Service not yet completed as they need to order a Timing belt and consequently a Cam Cover gasket

Good to hear most of it has been sorted Rocky - to potentially save any further delays & ensure you don't have to revisit the front of the motor again (thus avoiding repeated significant labour costs), are they replacing the water pump when they replace the timing belt, & have they ordered if they don't already have it? Timing belt & water pump are typically replaced together to save on labour & the inconvenience of the car being unavailable again.

[bruce]

Good stuff it is fixed.

[Rocky]

Good point about the Water Pump, Clubman. I will ask when they come back to me with the quote for the remaining work. As you say, do all the related work now to avoid future known issues that require another dismantle.
I understand that with a 21 yo car it is all downhill from here in but its good to do a bit of preventative maintenance if possible.
I know the Alternator is good as it was inspected by my Auto Electrician when "the Problem" first occurred in March. That leaves Starter Motor, Fuel Pump and maybe electrics.

[93_Clubman]

Would expect timing belt & water pump replace parts & labour by a Mazda dealer these days to be $1k or so. Expect labour is at least $100 per hour & parts alone are over $400:
https://mx5mania.com.au/collections/eng ... belt-na-nb
https://mx5mania.com.au/collections/eng ... azda-na-nb
https://mx5mania.com.au/collections/reb ... zda-nb8b-c
plus water pump gaskets.

May be not all downhill - they're usually more reliable than we expect. Mines 30 next Sep & the only issue I've had was the deterioration of the metal connectors in the top in tank electrical connection (the so called 'black wire' issue) which provides power to the fuel pump & fuel gauge. Issue manifested itself one day out of the blue a bit over a decade ago by not starting. I replaced the pair of wires between the top in tank connector & the fuel pump & fuel gauge & all good.

[greenMachine]

Yes, water pump and the two pulleys, prolly 150 for the wp and 30-40 each for the pulleys. But its been a while ...

Do it properly, do it once.

[Rocky]

Got my quote for the remaining work - Timing Belt, Water Pump and all the associated bits and pieces. $1500. using Genuine Mazda parts or $1100. using aftermarket parts. I thought, 'What the Hell' it is the only major service the car has had or will have so I went for the $1500. deal.
I do less than 5K a year so by the time it needs another big service I will be 80yrs old and probably passing it on to someone else.
The whole process will have cost $1800. plus $1500. = $3300. but that is not too bad spread over 20 years.
The Mazda 6 is next off the blocks....

[93_Clubman]

Hey Rocky, did the remaining work on your MX5 get done, & if so how's it running?