Cranks, fires but wont catch. Why wont this MX5 start now?

[Bill K 111]

Yesterday it died within 30 seconds of driving it. Coasted to a stop. Cranks, fires, dies (as opposed to just crank, crank, crank...nothing) Take key out to walk home but decide to put it back in and try one more time. It fires up. Drives beautifully for the rest of the afternoon, even go out later in the evening in it.

Today. take it for MOT. It passes. Go to pick it up and it does the whole crank/fire/die thing. Towed it home in the end and it hasn't started yet. It is getting fuel (pulled hose off and cranked...fuel everywhere) and it is still TRYING to fire (so it's not the cambelt or petrol pump.) It definitely seems like something is actually STOPPING it from running (rather than it showing no signs of life at all.) It is a 1993 1.8 and the immobiliser has been bypassed a while ago. Have no experience with these cars so does anyone know what I'm looking for/common problems? Ideas appreciated.

Thanks
Bill

[Slinky]

CAS failure perchance?

CAS = Cam Angle Sensor, it'll possibly start but fail to run if it fails..

[Bill K 111]

Thankyou for that. I phoned mazda for a new one and they said it was a camshaft AND crankshaft position sensor combined. That's a bit confusing (for me anway!) I thought it was the one at the back of the engine at the top on the passenger side. Does that really read the crank as well? Does that seem right? (It's around £300 BTW)

Thanks

[GreenV8S]

I don't know how the sensor is set up on that engine, but it would be possible to set up a cam sensor so that you could use it as a crank sensor too, just by using the appropriate tooth pattern and having the ECU calculate crank position and cam phase from it.

[simon3000]

sounds like what happened to ours.that was the cam sensor.found a second hand one off ebay (£40 from an mx5 breakers),10 minuite job to replace and it is now running fine.if you do a diagnostic check for fault codes it should confirm your suspicions or at least help pinpoint the problem.http://www.mx5club.co.nz/maintenance/engine_diagnostics/ this should help.i think it showed up as 3 flashes(g signal).

Edited by simon3000 on Thursday 16th October 19:34

[Slinky]

GreenV8S said:

I don't know how the sensor is set up on that engine, but it would be possible to set up a cam sensor so that you could use it as a crank sensor too, just by using the appropriate tooth pattern and having the ECU calculate crank position and cam phase from it.

CAS is the method of ignition trigger for MX5 lumps... issues that affect it are CAS o-ring failures that allow oil to pollute the CAS or just plain CAS failure..

Always worth checking the connector for the CAS to ensure that it hasn't worked loose causing your symptoms..

[Bill K 111]

Thanks again all. I'm towing it to a trusted local garage tomorrow who offered their diagnostic services. Tomorrow I shall print this thread containing your advice before I leave.

Cheers

[franv8]

On these cars, it does the function of telling the ECU the position of both the crank and the camshaft, because it knows that mechanically the two are connected together, and also that the crank turns twice for every cam rotation, and that they will always be in phase (else your cambelt just snapped...)

It is a ten minute job to change*

(and another 30 mins of resetting the ignition timing...)

[skinny]

mine does that if i leave the airflow meter connector off - you might have a dodgy connection on that (if 1.6)

[MX-5 Lazza]

skinny said:

mine does that if i leave the airflow meter connector off - you might have a dodgy connection on that (if 1.6)

1.8 has a hot-wire type mass-airflow sensor rather than the flappy AFM of the 1.6. Whenever I've seen this fail before it's brought up a CEL (engine warning light). They are pretty reliable too so if it's a 1.8 this would be an unlikely problem area. More likely to be a problem on a 1.6.

[Bill K 111]

Sorry to bump. But a final thanks to everyone who helped with this. It WAS the cam sensor. A s/h one from a specialist breaker for £40 and a local garage to fit (inc Auto Electrician to confirm it first) was £58. I printed this thread so clearly they looked at that first hence I'm sure my bill was much smaller than it could have been. Thanks again.

Bill K

[franv8]

Glad to hear it!

[arfurdaley]

My '94 1.8 has the same starting problem!! Turn the key, fires for an onstant, then dies, crnks but no further firing. Stop, try again, same result. This was a sporadic problem over the last 6 months, and the car would always eventually start, after 3 or 4 attempts. Then last week it decided it wasn't having it at all!! After a fruitless day checking all the connections I could find, I decided to bump it off. It fired straight away, and now starts on the key again, but for how long? Cam position sensor sounds about right to me, I have a Supra Turbo that did something similar 5 years ago. Where can I buy a secondhand sensor? Having bought a new one for the Supra (a second mortgage is required if you buy from Toyota Dealer!!) I,m not going down that route again. Help!

[Slyjoe]

Thread resurrection again - this sounds like my car - bugger to start but only of a morning, every other time I try its fine.
If it was the CAS would the problem be present "every" time I tried to start?
It's had new plugs and leads this weekend, and when running is sweet as a nut!
I've spoken to the previous owner, and its had a new coil pack too.
Any suggestions welcome..
Thanks.

[Sudad]

My mx5 cranks but engine does not start, mechanic suggested to replace the camshaft sensor, but still no luck still the same crank but does not start, the funny think about it after 36-48 hours the car starts no problem and then it dies after one working day and it goes back to crank no start till I leave it for a good few hours. Any body has an idea can help. I will be grateful.

[renaultgeek]

Bill K 111 said:

pulled hose off and cranked...

5 years and I'm the only one immature enough to notice this?

[Sudad]

Can you explain more, which hose do you mean? thanks