I know some of you guys have V6 engines with non-standard exhausts. What sort of CO levels are you getting during the emissions check that's part of your MOT test? The test station should give you a print-out. Also, has anyone had to replace a catalytic converter, and used a non-Mazda unit? Some places can supply a "sports cat", which is supposed to keep the CO level down but allow better air flow. I've just had one fitted and I have serious reservations about it, the car only just squeezed through the emission check. The reading was 0.19% CO, but the local Mazda dealer says a ZXi should be more like 0.02%, which is a big difference.

I have a high flow sports cat. In theory, it should keep emissions down to the level of the standard cat, but I haven't had it tested yet (MOT due in Oct). Are you sure it's down to the cat? Did you have your figures checked immediately pprior to fitting the new cat?

not had mine checked yet with exhaust on so I dont know, will see if I still have CO2 reading from original tho

The car failed the MOT miserably with a CO at fast idle (2700 rpm - now part of the test) of over 0.6%. Replacing the cat brought this just within the limit for a pass (0.2%), but Mazda man reckons this is still too high for the car.
by the way note it's CO not CO2 they measure now....

Ok, just passed my MoT on Fri, here are my results from the V6 (type R)
CO % vol 1.018
HC ppm vol 335
CO2 % vol 14.59
O2 % vol 0.75
Lambda 0.988

But as an import I get better limits anyway - CO % <3.500 and HC ppm <1200

p.s. these results are WITHOUT A CAT! :twisted::twisted::twisted:

Rob your limits are WAY higher - the UK spec has lambda at 0.970 to 1.03 (mine 1.009) and HC at 200ppm (mine 59ppm).

Yep, the bonus of a rare import! :twisted:

Have been thinking that if the CO level is still high with a new cat then maybe one of the lambda sensors is failing. I think I read somewhere on this Forum that they can become inefficient due to carbon build-up, so that's something fairly easy (and cheap) to check. Also you can measure the electrical resistance of the sensor, which if it's above a set limit means the thing is faulty.