MOT Problem - CAT Bypass

The most common problem people have at MOT time is exhaust emissions failure, mainly owners who have a de-CAT pipe. Here's some tips to make sure you don't have this problem.

The purpose of the catalytic converter is to reduce harmful emissions release into the atmosphere, but it also chokes the engines performance. For this reason many people have them removed and replaced with a straight-through bypass pipe. This removes the restriction, but clearly makes for fun-times when it comes to the dreaded MOT!

The main problem is that either the MOT station are ill-informed, or they can't be bothered to check out exactly how a car is to be tested. Current MOT legislation states that if your car was first registered between 1st August 1994 and 31st July 1995 (ie an M-registration), and it cannot be found in the emissions testers database (which the FTO, being an import, will not in the majority of cases), then it should be tested as a non-CAT car. However, most MOT testers, for whatever reason, simply try and find the nearest model car in their database to test against - usually a 1995 Galant or something similar, which results in the car being tested as a car with a CAT and it therefore fails. This is wrong!

It can also be very hard to persuade Mr MOT Tester that you are correct in saying it should be tested as a Non-CAT, so if you go to www.motuk.co.uk/exhaust_emmissions.htm you will find a handy flowchart, which is the same flowchart the MOT tester should use to determine how to test your car. Have him follow the questions and see that in fact you were right! (but don't get too cockey as he may smack you in the mouth!)

That's all well and good if you have an M-registered FTO (which a large %age are). If not, then you only have one real option - keep your old CAT, and fit it before you go to the MOT station.

Another useful hint is to make sure you take the car for a good hard drive before being tested, this makes sure that the emissions are lower. Have you ever noticed how when you get an emissions report, often they do 2 tests and it fails the first but passes the second with flying colours? That's because the engine is hotter second time round!

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