Had my MOT on Monday and am confused around readings.

Last year my MOT emissions reading was 100mg , after doing the recommended 15 mins at over 3krpm before test however this year my reading was 92mg.

While I am chuffed that my emisiions are well below the skoda stated, it is a bit annoying that these readings now put the car into zero rated road tax and I cant have that :thumbdwn: :(

What puzzles me is that these readings have decreased so much in a year, I would expect them to be very close in reading. Anyone any suggestions ?

added info :- car is remapped + Cupra intake, dont drive mad, but do like to keep turbo spinning before using the torque to pull away, in this mode change gear at 3.5k rpm max, verry occasionally will wait till 4k rpm.

Interested in your comments.

Diesel? Hmmm. The only thing I could think that is being measured here with a figure like 100mg is CO2 which for "Environmental" emissions (What your taxed on) is measured in g/km. You can't test that in a garage you can only check % (Unless kit has got a LOT better in the last 4 years)

The only emission test applicable to Diesel engines is the measuring of exhaust smoke density. The diesel smoke tester is measuring the density of the emissions (which is expressed in m-1) where the 'm' is for molar volume. The vehicle is revved up to max of six 'free accelerations' to get the average(mean) reading of the last three readings. I belive the current limits are as follows non-turbocharged engines no more than 2.50m-1 and for turbocharged engines no more than 3.00m-1. Vehicles first used before 1st August 1979: Exempt from metered smoke testing, but must not emit "dense blue or clearly visible black smoke for a period of more than 5 seconds at idle" or "dense blue or clearly visible black smoke during acceleration which would obscure the view of other road users".

If your MOT tester has put it on the other kit for petrol cars (Which is the only way you would get CO, CO2 or NOx readings as they are not required for the diesel MOT) then it just won't be accurate because the gasses are slightly different and it means nothing in the real world as the vehicle isn't under any load. Any "measured" emmisions won't bear any resemblance to what really comes out when driving and in relation to the stated taxable levels you think the car acheives.

Phew, I said all that in one breath!

Decron, you really ought to get out more

Decron, you really ought to get out more

At 2 in the morning?

Up with baby...

On the Dervs those mg are probably not CO2 readings but soot density readings.

After all the MOT test only tests for soot.