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I had a most embarrassing and puzzling sudden loss of engine power this afternoon and I was wondering if anyone else has had a similar experience and can provide some clues about the problem.

I had just overtaken a couple of very slow compacts that had just started up the steep climb on Pine Creek Road, near Springbrook-Mudgeeraba. I guess they were travelling at about 40-50kph, so I wasn't exactly hammering it to get by. I had been trailing them for about 5kms before that working 3rd & 4th, waiting for a suitable overtaking spot as the road was steep and twisty in parts. When the chance came I zipped back to 2nd and changed up on the way passed. The SP seemed to misfire and I thought I'd over-revved it, but knew that I hadn't been that aggressive. Anyway a few hundred metres further on after I'd cleared the slower cars the SP suddenly lost power and started misfiring. The loss of power was complete and I couldn't continue further so I had to pull over as best as I could trying to figure out what the problem was, then the car stalled.

The embarrassing bit came as the slower cars putted on by tootling me as they went up the hill .

A couple of turns of the key failed to get the engine started.

1. A quick look under the bonnet didn't reveal any strange sights, smells, fumes, or smoke.
2. No signs of anything loose, or not in its normal place.
3. Plenty of fuel in the tank (always used BP Ultimate)

As I was pulled over in a very awkward spot, I immediately called the RACQ for assistance. After the call was processed the BOV suggested I try restarting the car, which was against my better judgement as it sounding like a catastrophic failure to me. However, the car restarted and sounded normal. We were able to drive it home without incident (...cancelled the RACQ request of course).

1. What is the likely cause?....fuel, electrical, ECU, heat build-up?
2. I hadn't been driving the car hard, well any harder than I normally do.
3. The only mods to the engine is the SP T-Piece mod.
4. The car has been regularly and recently serviced.
5. Engine bay was dry, no rain, nor any water on the road.
6. Nothing was touched, or replaced, tweaked or fondled between the initial failure and the restart, which would have been about 5mins, 10mins at the most. So what happened during that period? Temperature drop? Fuel replenishment? What else could change with just the passing of time that affected this situation (...other than the BOV getting a bit more that very stroppy)? ECU reboot? (...do they do that?)

It seems odd to me that such a catastrophic failure could be self-correcting.

Has anyone else had a similar failure? Can the problem be analysed? Any clues before I seek assistance from Mazda?

FYI:

- 2002 MX5 SP, engine is stock other than the T-piece.
- just covered 62,000kms - regularly serviced.
- ambient temperature on the day ...about 23-25C, not very hot, and not excessively humid for Queensland.
- the car has never missed a beat, except one very brief glitch attributed to some dodgy fuel returning from NatMeet at Easter.
- car continues to restart ok.
- I did almost run out of fuel once whilst at Natmeet and then again on the recent Bum-Freezer weekend in July, but I've used the car many times since then, so I am assuming any fuel tank debris would have made its presence felt earlier.
- Oh, and I've recent had the battery changed, ... I seriously doubt if this would have any affect on electrical components, but I mention it in case any item is susceptible to problems after a change.

Totally clueless (...as usual)

coil packs maybe?

By "misfiring" was it spluttering like it was running on the last drop of fuel?
If so, first port of call would be the MAF. Check the inside is clean of debris. Unplug the sensor plug and give it a light spray of contact-cleaner or WD40 or the like, and brush it clean with a soft tooth-brush or paint-brush.

Check/replace plug leads, plugs or coils on plugs. The plugs were probably changed on time as part of the regular service but the leads and coils may not have been - check the old invoices to see what was actually done. I remember when the plug leads died on the NA years ago that it felt like catastrophic engine failure.

Thanks for the tips guys. These suggestions all seem logical starting points for analysis, but what I find really puzzling is the effects were only temporary. I would have thought the failure of any of the components mentioned would not be self-correcting as what appeared to happen. That is, failure of leads, plugs, coils, etc would be unresolved without replacement. I've had all these items fail at various times on different vehicles over the last 40 years driving, but I don't recall any fixing themselves without intervention. The car actually chugged to a stop - I would be surprised if a single plug/lead failure would cause that. That implies multiple components failing at the same time, then a miraculous restoration.

It's not unknown for leads to start working again after they cool down.

Also a faulty cam angle sensor mounted on the rear of the valve cover can fail if things get a bit warm then miraculously start working again after it cools down. Unfortunately a faulty one may not produce an error code in the ECU so diagnosing a faulty one can be difficult.

Also, get your fuel pump checked for pressure and flow. Mine started to fail at around 80k km. It's doing a lot more work in an SP than it is the stock car.

Yep, what Garry says about the cam angle sensor - skulzer had problems with his a year or so ago under similar conditions. Easy to replace.

Sounds like the same problem as all NB8B with the VVT!

The dreaded Cam Angle Sensor

Have a look HERE
As the SP uses the same sensor, I'm guessing they will have the same issues.
One of the MX5 Vic members has already replaced the sensor in his SP at about the same Km's.

Also known as 'got buck" on the big forum, read through what this guy did to isolate the problem!

I would recommend swapping it out with a known good sensor before blindingly spending money on chasing other possible causes.

Worked for me.

Thanks for the tips chaps.

After researching the links provided I'm leaning towards it being a CAS fault as the symptoms closely match what I experienced. I'll do some practical investigation on the weekend and I'll post an update. Failing that, there are a few other possibilities to examine, otherwise it's over to the pros (...assuming I can drive it there that is).

Cheers,

Mr Darbs, source a replacement CAS from eBay US as I can't imagine how much Mazda Aus wants for one.
Not that you're short of the folding stuff, but hey....

On an slightly OT note, I wonder why Mazda persisted with the design of the NB CAS throughout the end of the range as it's obviously crap-o-la.
I heard the crank-angle sensor can go awry as well.

1red5 wrote:Not that you're short of the folding stuff, but hey....

Ha! I wish - I'll have to see if the BOV will release some prisoners* for this.

[*= the affectionate term use for money in the Darby household]

I think it will be a process of elimination starting with the CAS. The other suspects, including the Crank Angle Sensor, will be targeted in due course.

Before you shell out your hard won 'prisoners' swap your cam angle sensor with another one (from a conveniently parked NB8B, say at a dodgy day or friendly weekend visit)to see if it changes anything. Be careful unplugging/plugging it in - that is how they break. The socket hangs off the side of the sensor and is unsupported, so pushing the plug in can break the socket off the side. Mania have new ones listed at $160 from memory, MX5 Parts in the UK have them listed at around $80 but won't have stock for a few weeks. The crank angle sensor is unlikely to be intermittent or heat affected - it is always hot down there. A data readout from the diagnostic connector would also help pinpoint the problem.

The CAS failure on an NB8B that I witnessed was only happening on slowish uphill crawls (i.e. Springbrook and Mt Tamborine) in summer conditions. The engine would die then fire up again after a 10 minute rest with the bonnet open.

I once had a similar problem with my SP some time ago.
I was accelerating hard when all of a sudden I lost power.

The car went sort of OK with small throttle inputs, but wouldn't boost at all.

Turned out the problem was a tube for the PCV valve got blown out from the cam cover, because for some reason, the car overboosted and blew the tube out.
Was a simple fix, just pushed the tube back in and it never happened again.

My first thought was coil packs but so much really useful advice.

Members so willing to help each other out is what makes this forum so great.