MOT Emissions fail - thoughts, please?

[Avocet]

Could I ask for thoughts on the attached, please? Not mine, just trying to help someone out on a Facebook group. 1993 (ish) car with a cat. Lambda is perfect, but HC is a bit high, and CO is very high. The poster said the cat "looked quite new". Recent new plugs and leads. Says the exhaust is new, but a "performance" one with fewer silencers.

As the lambda is good, I'm wondering whether his cat is actually doing anything?

 

[Belle427]

Aftermarket cats especially the sports variety need to be positively glowing to stand any chance of passing so it could be that simple.

 

[Mottie]

At certain testing stations when they had a problem like that, if they are not measuring the engine speed, they'd just let it tickover on the second 'fast' idle test and pull the probe out for the CO at idle test. Just sayin'

 

[Avocet]

Aftermarket cats especially the sports variety need to be positively glowing to stand any chance of passing so it could be that simple.

I suspect that's the problem - if there's even a brick inside the can! The cheapo aftermarket cat manufacturers know that the MOT test can't even check for NOx, so they leave those expensive chemicals out altogether. I also get the impression they really skimp on the oxidation chemicals too, in order to save costs.

 

[Avocet]

At certain testing stations when they had a problem like that, if they are not measuring the engine speed, they'd just let it tickover on the second 'fast' idle test and pull the probe out for the CO at idle test. Just sayin'

Well, I guess he could offer them some extra payment for that test method...