at these readings its not the cat
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If it's the tappets yes this might well have a negative effect on emissions due to incorrect valve opening / closing sequences. It might also occur if the camshaft is worn. The fact that at higher revs the problem diminishes may be attributed to the the ignition timing compensating for valve-gear wear. 111k miles is not exactly new...this kind of wear is normal on a petrol engine. At this point I feel compelled to suggest you check all the major components for wear, like pistons and piston rings. Does the exhaust smell like burnt oil? Are power and economy OK or have they diminished? Does the engine misfire or experience a flatspot during acceleration? Sorry but I'm asking because at 111k miles you can't expect ANY part of the engine to be in A1 condition, and if the valve-gear is worn you can most certainly expect the crankshaft assembly to wear in a parallel manner. If it's a carburettor try exposing the intake, starting the engine to fast idle and spray a can of carb cleaner directly into it. This can clear gummed-up deposits inside the carb. How do you drive? Do you change gear early and commute slowly in traffic or do you drive mostly motorway constantly above 2,500 rpm? Have you checked the spark plugs for signs of rich mixture?
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Thanks again Stan! Ok to go through your points; will ask Dad to check pistons & rings and spark plugs. Exhaust has no smell at all. Power and economy are fine - no change. No misfiring except when the engine is just idling. No flat spot in accelaration- plenty of power. Drive a mixture of town and motorway /dual carriageway at 80ish. Rosa
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A misfire at idle will cause the emissions failure and you need to find out why you have the misfire, solve that and I suspect the emissions problem will go away.
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misfires don't cause high CO.
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misfires don't cause high CO.
You appear to not have read the persons post. The above comments not in context and not after reading what the OP has posted...certainly the comment is Troll like and unhelpful in helping them solve the problem.
If the fuel/air mixture is incorrect (too rich this) will raise CO levels, this can cause the engine to run rough (often interpreted as misfiring). This is especially so if the problem is due to:
Injector Problems
Airflow problems
ECM bad/incorrect signal input from another sensor
etc.
The cat will reduce this quite a lot, so it will have to be fairly bad to cause the rise in CO and hence the possibility of rough running..I don't think it's an ignition problem, because if so then there would be a rise in HC levels, and the OP does not state that there is such a rise. Howver if the HC have also risen a little, together with a big rise in CO, even more reason to suspect a mixture problem and rough running at low revs. 2.27 %is well on the way to rich misfire which starts around 3% CO (and we don't know for sure how much the CAT is reducing this), certainly the OP engine will be running rough (and the OP description of "lumpy" idle would seem to confirm this.
I'm trying to keep it simple for the other person, hence not posting like this....they need to take it to a garage and have the source of the rough running investigated, fixing that should fix the CO problem....either way for the benefit of the OP, the problem is probably fuel/air mix being too rich e.g. too much fuel or too little air, cut it either way you like.
Edited by davecuk on 01/10/2009 at 01:39
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Hi,
Before you go through lots of expensive things to check and change, you've given us no indication as to when the vehicle was last serviced. We have 3 cars in the family and each gets a full service just prior to MOT. People forget the importance of new plugs, air and oil filters and a change of oil is. If any of these have not been done, then get them done asap. Any one of these items mentioned can contribute to an MOT failure.
When returning it for MOT make sure its given a good thrash through the gears for a minimum of 10 miles (it would certainly help your car).
Hope this helps
Robin the Technician
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Many thanks for all your suggestions Dave and Robin. Have booked car into local independant garage for one final go as to where the problem might be. Will certainly talk to them about cat and airflow probs. BTW the car is regularly serviced every 10,000 miles or year which ever comes first, so think it is *unlikely* to be that, but atthe mo I'd try almost anything!!
Thanks again guys for your time to reply. Rosa
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Please let us know what is found.
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regularly serviced every 10000 miles or year which ever comes first
fit a new air filter
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