My Clio has failed its MOT because it's polluting... I've got the four gas analysis and was wondering whether anyone knows what to make of it. I've changed the spark plugs and filter and put in an additive, and although the values dropped from the initial fail, it's still not good enough:
Acceleration (max CO 0.3, max lambda 0.97-1.03)
CO 0.92
Lambda 0.978
Co2 14.4
O2 0.18
HC 90
And
Idle (max CO 0.5)
CO 0.54
CO2 13.2
O2 1.93
HC 169
I live in France so I'm not sure whether acceleration and idle are the correct ways if translating the two tests but I hope you might recognise them from UK terminology (I've never had to MOT a car in the UK). I'm stuck and don't know what to look for next. Does the high CO suggest catalytic converter or oxygen sensor...?
Any thoughts...?
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Both CO & HC suggest dead cat.
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Thanks!
Another mini-question. A friend stalled my car a while ago and put jump leads on to restart it... but the wrong way round... This meant the ECU got fried and they got it replaced with a secondhand one from a breaker's yard. With the pollution problems, I suddenly got curious about this misadventure and checked the numbers of the models... and it turns out that they aren't the same... Is there any chance at all that an incorrect ecu might contribute...?
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Hydrocarbons (HC) is unburned fuel and measured in parts per million (PPM). The maxim limit for MOT is 200PPM. Theoretically this figure should be zero, although it never actually is since not every last scrap of fuel will ever be burned. Gas analysers sometimes read zero when the HC is barely measurable, but in reality this is near impossible to achieve. A high HC figure indicates inefficient combustion, possibly due to an engine misfire, vacuum leak, low fuel pressure, or loss of cylinder compression.
Carbon Monoxide (CO) is produced when petrol is burned. A rich fuel/air mixture consumes more oxygen than a lean one, and consequently more CO is present. The maximum limit for MOT is 0.2% CO.
Before you condemn the catalyst I would use a scantool and do some fuel trim checks. Make absolutely certain you have no vacuum leaks or anything obvious that would make the ECM respond to a lean running condition by adding fuel. The Short Term Fuel Trim and Long Term Fuel Trim will give you a very good indication of how the engine is running, and what the ECM is doing to correct it if it isn't running properly. If everything seems ok then try some Cataclean in the fuel tank. Follow the instructions on the bottle. It may improve things.
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