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kingnr
Original Poster
6 posts
20 months
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Hi all, Please can you help my mazda mx5 1.8 has failed its MOT on the emissions test. The CO emissions read 0.606% when the limit is 0.300%. How do I know if it needs a new Cat or a Sensor? Would you take it to a mazda dealer or get it checked independently? Please recommend a garage in london area if possible. Thanks in advance, Nick 
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Hol
378 posts
69 months
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Looking at those results, I would say that your Lambda is out of the tolerance level and that needs to be replaced as it is fooling your ECU.
Once the lambda is working correctly you may find the o2 levels come down as it adjusts the fueling down.
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MX-5 Lazza
6,462 posts
88 months
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Could also be the engine temp sensor on the back of the head. If the ecu thinks the engine is colder than it is it'll run rich.
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kingnr
Original Poster
6 posts
20 months
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Thanks for your responses - its a topic I know little about! Your feedback will be useful when I take it to the garage.
Any other ideas would be most welcomed.
Thanks Piston Head’ers!
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MX-5 Lazza
6,462 posts
88 months
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Blocked air-filter (it would have to be pretty bad), plugs/leads, TPS, even the clutch switch can cause fuelling issues. Start simple and cheap though.
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skinny
3,375 posts
104 months
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unless you've poisoned it (and that's only done with leaded fuel or fuel additives) your cat will likely be fine.
as others have said, it's either a duff lambda sensor or temp sensor. last alternative is that it just needs an italian tune-up.
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