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MG MGF Technical - Emission failure on MOT


My 1999 MGF VVC just failed MOT on Emissions. Car is running K&N filter, new oil and plugs. Its been gararged for 18mths but had a good hours Pre MOT thrash at the weekend.

The wife suggests a trip to the breakers is in order.

Readings are as follows

Fast Idle
CO 0.582 fail
HC 172 Pass
Lambada 1.004 Pass

Second Fast Idle
CO 0.504 fail
HC 65 Pass
Lambada 1.005 Pass

Natural Idle
CO 0.384 Pass

CAT looks like it has seen better days and will probably require the services of an angle grinder to remove.

Any advice as to what are the potential causes of co failure would be gratefully received.

Many thanks.
R Eatough


Sounds like the CAT to me.

Have the same set up on our VVC too and ours failed the first time last week too - but I didn't get it hot enough!

After an early morning 'italian tune up' it sailed through - only hope there weren't any cameras on that stretch of road!(how do you redline it in all gears without breaking the speed limit?)

Had the new CAT last year though but it only cost around 60-70 and that was through a garage.

Chris Bond

I got one of these - - seems to work OK, though it needed to be slightly modified to fit my non-standard system.
Mike Cunningham

I imagine the VVC is the hardest to get through emissions, the 1.6 and 1.8 have so much turbulence in the flow through the head that they can reportedly pass without a cat. It also helps economy,does nothing for performance though. I'm not sure you need to redline the car in all gears to get the cat working nicely, a brisk entry to the motorway followed by a few miles at the legal limit should work, I agree its less enjoyable. One reason the car seems livlier after quick blast is ECUs learn yuor habits so if you waffle along, the car concludes thats how you want it set.
Stan Best

Had the same problem a few years ago. If you can disconnect one end of the cat, check that the filling is still there, mine was empty!!! The fill is a 1mm Approx fine square 'mesh'. If that's ok It could be the engine management temp sensor. Does the radiator fan come on if not then it's likely that it has failed and the car is running in cold mode. It can also be the lamda sensor, not sure how to check this. Be very careful in the one you buy as the car only likes the ones design for the rover system. Catchall ones won't work. Good luck.
JR Mailer

Hi thanks for the posts.

Took cat off with the use of an angle grinder.nothing left inside.

Replaced with a 40 ebay version and one of thoes 200 quid stainless steel exhausts also from ebay.

The brackets holding the exhaust mounting rubers in place are completely corroded. will require the Angle grinder again and some new brackets and rubbers from Brown and Gammon who where most helpful.

R Eatough

This thread was discussed between 29/03/2011 and 22/04/2011

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