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Mot failed 3times with high emissions

11K views 12 replies 7 participants last post by  Denys Milano 
#1 ·
Hey guys the trouble seems to be never ending with my mini 1.4 r56 at the minute. It had valve seals done recently and went in for mot and failed due to high emissions we were told to use cataclean did this and drive about 30miles in it then put it in again it failed. We were told new cat so fitted a new cat and still failed!
The mechanics said could be pre cat sensor or post cat sensor he doesn't know for sure. Anyone had this before and could recommend which one it may be? The car runs great and no oil from exhaust since valve seals have been changed

Thanks
 
#3 ·
Thanks for responding. It had an oil change and spark plugs before it went in for first mot. I think the air filter needs changing though so will do that. I've ordered both of the sensors just to try and get it sorted as I'm fed up of having no car!
 
#5 ·
Your mechanic really ought to have got the diagnostic readings before recommending replacing things like the catalyst or the Lambda sensors.

The Lambda sensors can be working okay, but the connection wiring and plugs into the ECU can be dirty or corroded so give false readings.

On my MCS, the Lambda sensors are definitly NOT currently reading correctly and it is running rich, but it is still passing the MOT emissions test okay.

You ought to check for air leaks on the manifold and exhaust system as well but a new or cleaned airfilter might do the trick on its own.
 
#7 ·
Thanks for the advice everyone the mechanic said there is no codes showing so he's a bit baffled aswell. Here are the reading
It passed on natural idle test

Fast idle test co 0.79%
Hc 391ppm
Lambda 1.02

Second fast idle test
Co 0.82%
Hc 405ppm
Lambda 1.02
 
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