TVR MOT Emissions testing - higher limits allowed for TVR!
Discussion
I have a TVR Tuscan and previously have had issues with falling to meet the emissions test for the MOT, not with the CO reading which has always been virtually zero, but with the Lambda readings. The Basic Emissions Test (BET) has limits for all cars used after August 1992 fitted with a catalytic converter. This test requires CO to be less than 0.2% and the Lambda to be between the ranges of 0.97 and 1.03 when at fast idle. The Lambda range limit can be tough for a TVR Speed 6 engine to pass. If it fails then don't despair as the tester should then carry out an Extended emissions test using the VOSA guide to look up the make and model of the car.
Current edition is the 18th edition see here https://www.gov.uk/government/uploads/system/uploa... and this lists on page 147 the various TVR models including Tuscan, Tamora, T350 etc.
The guide gives an allowable range of 0.3% CO at fast idle AND a Lambda range of 0.9 to 1.2! This is much higher than the standard 1.03 maximum on the Basic Emissions Test!
So if you go for your MOT and it fails the basic emissions test, make sure you get the tester to carry out the Extended Emissions test and looks up the model in his guide. Better still, print it out and take page 147 with you!
Current edition is the 18th edition see here https://www.gov.uk/government/uploads/system/uploa... and this lists on page 147 the various TVR models including Tuscan, Tamora, T350 etc.
The guide gives an allowable range of 0.3% CO at fast idle AND a Lambda range of 0.9 to 1.2! This is much higher than the standard 1.03 maximum on the Basic Emissions Test!
So if you go for your MOT and it fails the basic emissions test, make sure you get the tester to carry out the Extended Emissions test and looks up the model in his guide. Better still, print it out and take page 147 with you!
You may find that the issue with the Lambda testing is a very simple one. The Tuscan 'motorbike' exhaust cans have a large bore - much larger than is needed for the exhaust gas flow at fast idle. What happens is that air is drawn back in to the exhaust system and this throws off the lambda reading as it is reading the Oxygen in the air. Your tester may see this as the reading gets better as he inserts the probe further into the exhaust.
The solution is to partially block the exhaust pipe around the probe with a rag. No need to completely block it, just leave a 1" dia hole or so - and magically, the Lambda reading will fall into the correct range.
Regards
Phil.
The solution is to partially block the exhaust pipe around the probe with a rag. No need to completely block it, just leave a 1" dia hole or so - and magically, the Lambda reading will fall into the correct range.
Regards
Phil.
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