Mot fail

[Xsikid]

This is of another forum im on may help with sorting it

Cars can fail the emission test for a number of reasons, could be down to using an open air filter/induction kit
or could be down to using a sports exhaust. Some de-catted cars may pass, but this is due to the mechanical condition
of the engine and how its been looked after. Alot of people say replace the cat, when infact it doesnt need a new one.
Firstly check your emission sheet and see what readings are on it, or if you dont have one refer to the VT30 (failure sheet)

High CO and Low Lambda... is rich mixture which is caused by a missfire, faulty oxygen sensor, blocked air filter

High Lambda and high O2... could be the cat but check the oxygen sensor is working, there are no leaks in the exhaust, and could be caused by using an open air filter/induction kit, Air leaks in the intake system, faulty map sensor, could also be down to poor engine condition and maybe cured by a service

High HC (hydrocarbons) ... with good CO probably a missfire, poor engine conition, with high CO fail and a low Lambda the mixture is rich

CO high, lambda high and O2 high... cat faulty (or Intake leaks etc)

Lambda fail... if a high fail faulty oxygen sensor, weak mixture, hole in the exhaust. if a low fail then faulty oxygen sensor, rich mixture or misfire

Before replacing an oxygen sensor you can remove it and check it visually, and test it if u have the correct equipment

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Wow that's given me a lot to look into many thanks. Iv got all the readings from mot do I can get things rolling . Thanks again

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CO is likely to be the cat though if the cat is got really hot it may pass, Lambda is usually out due to a exhaust blow

I put a new cat on with lambda sensor about 3 years ago but have only just learnt that they don't really last that long!! So I have a list of things to try tomorrow then it's retest this Friday. If it fails then I will put a new cat on and also spend some time getting all the parts Iv gathered fitted. Ready for summer fun