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Discussion Starter #1
Having problems with my JTS hot starting. OK - so I know the prime suspect is normally the crank sensor - I had that with my old 156 Twinspark - but I am looking to see if there is another explanation: partly because I have already changed the crank sensor (which could of course be faulty) - but the symptoms are IDENTICAL to the old sensor, notably: It has NEVER stopped once running (which my old car progressed to dying quite quickly). It ALWAYS starts from cold - the problem I have is after it's fully warm, is switched off and parked for 15-45 minutes. Occasionally it has been a pig to start immediately after switch off (my daughter is learning to drive in it - when we have been pootling round town at learner speeds and she has stalled, it has been difficult to start!
The other difference: I have plugged FES in when it has been objecting to starting - the crank sensor is registering (300rpm on the starter - is this reasonable?). At the same time the injectors show zero opening time.
I should also say that the cam sensor keeps throwing errors (P0340) - although engine (generally) runs fine.
So, question to the great and the good of this forum - are my symptoms only explained by the crank sensor giving the wrong signal? Could the cam sensor by involved (P0340 errors have been around a couple of years - hot starting issue about 4 months). Is there something else I should do before getting another crank sensor?
Thanks - and sorry for the long rambling post!
 

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I'd say the cam sensor needs changing anyway, but as it is under the exhaust cam wheel that's quite involved, how far are you off a cam belt, tensioners and water pump change? if not far then it would be an opportunity to do the sensor as well. If not then try another crank sensor as it's not as time and money consuming, also check any associated wiring for defects.

In the 'old days' the symptoms you describe would have been down to vapour lock in the fuel system.
 

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Discussion Starter #3
OK, thanks for the reply:
I'd say the cam sensor needs changing anyway, but as it is under the exhaust cam wheel that's quite involved, how far are you off a cam belt, tensioners and water pump change? Not that close, sadly, about halfway. And I don't really want to incur the expense unless this really is the problem here - I can live with no cam sensing as the engine seems to run OK - it's the starting that bothers me!

If not then try another crank sensor as it's not as time and money consuming, also check any associated wiring for defects. - My feeling too - annoying if the replacement I already fitted is already faulty - I got it in a hurry (after my previous experience of one going totally bad very quickly) - I will get a genuine Bosch one, as I previously had trouble with non-Bosch ignition coils.

In the 'old days' the symptoms you describe would have been down to vapour lock in the fuel system.
Certainly feels like 'no fuel' - but I have fuel pressure and I can see 0ms opening on injectors - so yes, there's no fuel reaching the cylinders, but it looks like a decision by the ECU to not open the injectors
 

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I'd go with the cam sensor. Without the cam sensor, the ECU doesn't know what phase the engine is in which would be compression or exhaust stroke. For that reason, it won't know when to inject fuel but normally the ECU is programmed to get round it. I don't know if it is choose a particular phase or to split injection amounts but in either case, I think it would need the starter to be operated for quite a few seconds before the ECU realises exactly what is happening and then tries to get round it.

Once the engine is running, it is normal not to experience any changes even with a defective camshaft sensor. The only manifestation is difficulty in starting and lack of measured injection pulse is an expected symptom. 300rpm is an expected figure when turning over on the starter motor.

If the cam belt was done not too long ago (remember interval is 36k miles) and it was going to be reused, I don't see why the not recommended method of tippex marks on all 3 pulleys and corresponding bits on belt would cause issues. If fitting new belt, I'd do it right though.

In any case, the JTS is not a natural choice for a learner. The throttle seems non linear when moving off and it tends to produce a lurch quite easily unless one has a deft touch. I'm guessing your daughter will either learn to be very smooth and quite quick or simply hate Alfas.
 

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Discussion Starter #5
Thank-you for this - it does make sense. I suppose the heat can get to the cam phase sensor in the same way that it affects the crank sensor. I will look at my options...
As for the learner driver - this is my second daughter to learn on this car - it doesn't seem to have created a problem - quite the reverse for the older one - she wants a Guilia! (although not yet)
 

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Discussion Starter #6
UPDATE: Done the cam sensor - all sorted! - I did this a week ago and no further problems, either with hot starting or error codes.
The explanation below would explain why it never cut out - even when properly hot - as once running the ECU knows the stroke the engine's on. Whereas a crank sensor losing the plot when hot does cause the engine to stop. So, hanks Fruity for the confirmation.

I'd go with the cam sensor. Without the cam sensor, the ECU doesn't know what phase the engine is in which would be compression or exhaust stroke. For that reason, it won't know when to inject fuel but normally the ECU is programmed to get round it. I don't know if it is choose a particular phase or to split injection amounts but in either case, I think it would need the starter to be operated for quite a few seconds before the ECU realises exactly what is happening and then tries to get round it.

Once the engine is running, it is normal not to experience any changes even with a defective camshaft sensor. The only manifestation is difficulty in starting and lack of measured injection pulse is an expected symptom. 300rpm is an expected figure when turning over on the starter motor.
 
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