Thanks for the suggestions but all have already been considered with the exception of the "coil" failing when overheated: clearly a potential problem in other areas.
The Punto has a single point injection system which appears to consist of a single injector squirting metered doses of petrol into the throat of a carburettor body (devoid of bowl, float & jets) in response to a bewidering array of sensors whose data are processed by an ECU on the inner offside wing.
I suspect overfuelling and wonder:
Has the oxygen sensor in the exhaust pipe failed?
Is the engine temperatue sensor/ECU failing to reduce the petrol doses once the engine is warm?
Is there a sensor in the catalytic converter to protect it from overfuelling and would it help to disconnect this?
Further discussion on these points would be much appreciated.
PS I like fish n chips and crowds.
Heather
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Overfuelling is the most likely explanation. Surprising the Fiat diagnosic computer cannot sort this one out.
Try changing the fuel injector.
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If it is overfuelling, disconnecting the sensor that protects the catalytic convertor could be disastrous for the cat itself as it will be terminally damaged by the excess fuel. I would still consider an ignition/coil fault ,when hot, to be the most likely cause as discussed in the other thread running on this subject.
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NB. I asked Heather how the car stopped and she replied "it just stops dead, usually on the over-run.
Heather,
I have looked in my tech library and taken advice from a contact on this, here is all the info.
Your car is likely to have the Weber Marelli (6F?) engine management with single point injection as you mention. On the ignition side this a distributorless system with twin coils (a coil pack, looks more like a block shabed distributor) mounted on the end of the cam cover. Each coil feeds two cylinders.
Common faults.....
Tom is right that overfueling is a common problem with these engines but I'm still not sure that is your problem. However they can suffer failure of the MAP sensor which may cause overfueling. Over a period of time this can lead to failure of the lambda sensor, as well as the cat. Another odd reason for overfueling is problems with the valves gumming up affecting manifold pressure, in turn causing the MAP sensor to fool the ECU into delivering more fuel.........this also leads down the path of lambda and cat early failure.
Other issues....
It seems this setup has a true over-run fuel cutoff, I think many single point systems allow a small fuel flow to guard against a flat spot when you accelerate after a period of over-run. Could there possibly be a problem here where this fuel cutoff doesn't resume as it should after an over-run period. I have no idea what triggers the ECU into this mode, possibly the throttle position switch. But it is obviously electrical and could be affected by heat.
What about an intermitant fault with the engine immobiliser, has this been considered?
There should be an inertia engine/fuel shut off switch in the floor by the passenger seat, can you see a sort of grey button in the carpet. I have no idea why it should be mileage/heat related but has anyone considered this faulting which would give the symptoms you describe.
As I understand it, when you turn the engine over to start, the ECU looks for a signal from the crank angle sensor and it is that signal that then turns on the fuel pump relay and drives the fuel injector/ign coil outputs. If the crank angle sensor is breaking down with heat it again would give the type of problem you are experiencing. This can be a problem with many makes.
Overall I'm still inclined to look for an electrical associated fault caused by failure of a component due to heat breakdown. Why I don't think it will be a simple case of overfuelling is that cars will often go on like that for ages with odd performance issues but not stopping dead like yours.
I would welcome comments on the above, in particular from the Tune-Up boys. Where are you when I'm struggling??
David
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Sorry couple of spelling mistakes and it was Tim, not Tom, who was mentioning the overfueling.
Glad that Tribune girl isn't staying!
David
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Thank you,
There is no immobiliser on the car.
I like the idea of the inertia cut-off and will look for it tomorrow.
I have tried disconnecting the throttle position sensor and the inlet manifold sensor and neither made any difference
thanks for your patience
Heather
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David, I tend to agree with you. As a rule of thumb, fuel problems are characterised by a spluttering stop (can't think of a better description) whereas electrical problems tends to be more sudden.
ps, i was a tune up merchant in a previous life (around 15-20 yrs ago) but we had carbs and points and condensers in those days!
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Dear David
Which are the MAP & Lamda sensors?
Heather
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The MAP sensor is on the bulkhead to the rear of the engine, connected to the engine by a tube from near to the throttle body. This may be what you call the manifold sensor.
The lambda sensor is in the exhaust downpipe between the manifold and cat.
David
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Dear David,
So MAP = Manifold Active Pressure.
Why is the oxygen sensor called lambda? Has my car got Foot & Mouth? Will all the cars in the area now need to be scrapped?
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I don't know why it is called this, my understanding was that lambda is the Greek for wavelength.
A tech source explains it as follows.........
"called a Lambda (from the Greek letter that represents the ideal stoichiometric 14.7:1 air/fuel ratio by weight in engineering terminology), oxygen, O2, EGO (Exhaust Gas Oxygen), or HEGO (Heated Exhaust Gas Oxygen) sensor"
So that must be right, if it's not wrong!
You comment on eliminating components by disconnection, do you mean to clean the pin contacts? Even if an engine would run with various parts out of circuit, by removing them you are far from proving they are faulty. If this is the type of diagnostic approach favoured you need to substitite each in turn with a new or proven good unit.
You say there is no immobiliser on the car, do you have a "red key" as this is part of such a system.
I would still favour thinking about the immob (if fitted), fuel over-run cut out, inertia safety switch, crank angle sensor or ign (coils?) failure.
On a slightly wider note we have discussed similar driveability faults here before and agreed they are the price we pay for such electronic control. Many 3yr old + cars of all makes are suffering these problems and sometimes they exist right throughout one persons ownership of the car. The only "repair" being to sell it on.
Last thought for now, can the fault ever be reproduced in the workshop by extended fast idle running? If so watching it fail with the diagnostics gear hooked up should prove the fault.
David
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So, the engine stops when warm and on overrun.
If the overrun cut off is failing intermittently then this could happen at any temperature.
One thing that operates when the engine is at operating temperature is the evaporative loss emission control system. The control solenoid on this device should only allow fuel through under load. If it is also allowing fuel through on overrun it may trigger the ECU to shut the engine down to protect the cat converter.
This unit is situated under the driver's side headlamp and has blue pipe connecting it to the inlet manifold.
Try disconnecting the electrical plug to this unit
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So, the engine stops when warm and on overrun.
If the overrun cut off is failing intermittently then this could happen at any temperature.
One thing that operates only when the engine is at operating temperature is the evaporative loss emission control system. The control solenoid on this device should only allow fuel through under load. If it is also allowing fuel through on overrun it may trigger the ECU to shut the engine down to protect the cat converter.
This unit is situated under the driver's side headlamp and has blue pipe connecting it to the inlet manifold.
Try disconnecting the electrical plug to this unit
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Neat deduction Tim. Didn't realise the purge cannister discharge control was temp related. Hope it proves right.
David
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Heather/Tim,
I've been a bit slow here. You both have the same e-mail address so Tim........not to far to see Heather and tell her in person!
Oddly enough I mentioned to one of my contacts there was something of the spoof in this enquiry but decided it was impolite do make that assumption and tried to give helpful info. In any case there may have been some useful info come out of it for others following the thread, even if you didn't actually need help.
Going to be honest enough to say what you two are up to?
David
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