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SWMO's 1.4 Puma failed its MOT on emissions, CO level was 0.34% at fast idle, pass level is O.3%. At natural idle it was 0.61%, pass level is 0.5%. The HC was 27 ppm, and the Lambda value was 0.99. The learned MOT tester pronounced that the cat was dead and should be replaced. His view was that the Lambda reading show that the sensor is OK. However I'm concerned that whatever caused the cat to fail in the first place will cause it to go again. I've had the cat off and the matrix is place but does look sooty, as does the inside of the exhaust manifold. This would make me think that it's running rich, but then surely this would show in the other readings. Does anybody have any wisdom they can pass on?
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The fact that the lambda is about right shows that the lambda sensor is working. The failure figures are not all that high, so the cat must be working. Best thing you can do with this is fill it with quality petrol, then give it a good hard italian tune up, then re-present it for the test hot. Odds on it will pass....
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RichardW
Is it illogical? It must be Citroen....
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If you can source a pipe to couple the exhaust back up then have an emissions test done with no cat to see what the engine is really doing. Have you had a head gasket failure or loss of water or filled up with leaded fuel. Regards Peter
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A lambda reading has no connection with the lambda sensor, to think otherwise is a common mistake. The lambda reading you have would indicate the car is running slightly rich (your idealy looking for lambda 1) but before you spend any money on it give it a good pasting to get it nice and hot and see if the levels come down. Normaly if the CAT is shot you would expect a CO reading of around 0.5% although it could be getting tired.
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Thanks for the very quick replies. I should have said that those figures were taken on Tuesday following a weekend thrash of 75 miles and were identical to the readings taken at the MOT on Saturday. It's always run on Shell, mostly V Power, and uses 1/2 l of oil in 8,000 miles.
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Has the car been serviced recently, a change of oil and filter ait and fuel filters can make a big difference. I would also consider cleaning or replacing the O2 sensor before condeming the catalyst.
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Archie
Maybe the best move is to get a scanner plugged in and check that it's in closed loop mode and that the live-data isn't showing any aberrant readings.
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In these instances i usually find a clean of the map senser pipes does the job,pull the pipe off be carefull as they can break at the moulding and back blow the pipe to the inlet manifold check and a blast up the road and it should pass
it really annoys me when i read that the first port of call for some mot stations is to advise fitting a new cat, so well done mot man
map will be right hand side on the bulkhead if it has one as you stand at the front
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Thanks for all the advice. I going to work through the engine management system, checking connections and sensor cleanliness as suggested. As a fall back I have it booked in for a diagnostic check. I'll let you know the result.
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