Emissions, Cats etc.

[rustybin]

Afternoon learned ones,

I am just returned from getting, or rather not getting my Scooby through the MOT. It failed on emissions due to a CO of 1.75 rather than the proscribed 0.2 limit.

It is currently running a decatted down pipe but still has the centre cat', so my knee jerk reaction is to stick the down-pipe cat' back on. But then I got to wondering whether a high CO content wasn't just a symptom of running rich that the cat' may not have any effect on.

Incidentally it is also running an ECUTek ECU which has been remapped since its last MOT if that helps shed any light. There are no fault codes showing so I assume everything is OK in terms of Lambda and MAF sensors (I need a fingers crossed smiley).

Anyone any thoughts before I bolt the cat on re-mot it and take it off again?

Thanks in advance.

[350matt]

can you access the map? and try leaning it off at idle yourself?
1.75% CO is pretty rich at idle, my uncatted RV8 with a hot cam only runs 0.6% CO for a stable idle and I can get it down to 0.25% with it popping and banging

Matt

[stevieturbo]

generally speaking, the cat should remove virtually all CO emissions.

Thats not so say it is a fuelling issue though. But at idle, regardless of Ecutek or not, the lambda sensor takes control, and should leave CO at around 0.1% even without a cat.

I'd check the lambda sensor is indeed working properly first.

[rustybin]

Checked the lambda sensor and it was working OK. Put the Cat back on and it went through OK. CO at 0.03% at fast idle as compared to 1.75%+ without.

Thanks for the advice.

[Mikey G]

Out of curiosity, how hot was the car before you took it for the MOT first time? The first cat is mostly there to work when cool then the second cat will take over as it takes longer to warm up being further down the exhaust. Seen this happen before and generaly if you give the car a good ragging before the emmisions test you should be ok.

[rustybin]

Mikey G said:

Out of curiosity, how hot was the car before you took it for the MOT first time? The first cat is mostly there to work when cool then the second cat will take over as it takes longer to warm up being further down the exhaust. Seen this happen before and generaly if you give the car a good ragging before the emmisions test you should be ok.

When I first took it in they did all the suspension, lights etc. bits first then put it on the analyser. After about 30s the guy suggested 'roight I reckons you needs to take it fur a bit of a spin and we'll try 'er agin' He also suggested I turned left out of the garage as there aren't any cameras in that direction! It was ticking and clicking very happily the second time around and still no joy.