Hi All

First post here so hope this gets a reply or two! I have a Y reg Fabia Comfort, 1.4 petrol 8V. It went through the MOT last week absolutely fine which was a relief and I got talking to the garage owner about the test. I asked him about my CO results because I have a device fitted that I've swon by on three previous cars and wanted to see a neutral's perspective on this car.

My readings were:

Fast Idle (2767 rpm)

CO % vol

Max Limit: 0.200

Actual Value: 0.007

HC ppm vol

Max Limit: 200

Actual Value: 3

Natural Idle Test

RPM 811

CO % vol

Max Limit: 0.300

Actual Value: 0.010

Now to me, as someone that is looking for further proof the device I have is doing its job, these look like really nice low figures; and the garage owner agreed that for the car type they were extremely good. Queue warm fuzzy feeling that it was money well spent!

However, there's one thing I have no clue about.. does the carbon monoxide level being low (efficieny of burning) translate to a lower carbone dioxide CO2 level necessarily? I'd love to put the car through a Vosa reassessment (which apparently costs about the same as an MOT) and bring the vehicle down from a god-awful Band H @ £195 / yr due to the 173 g/km. But is it just optimistic thinking on my part that the two emissions levels are related?

Has anyone else undergone this re-test with Vosa? Is the garage owner about right with the figure and was it worth it? Cheers for any advice

... does the carbon monoxide level being low (efficieny of burning) translate to a lower carbone dioxide CO2 level necessarily?...

No; in a word.

Low CO level just means everything's working as it should be, i.e. no significant faults with engine/ECU/lambda sensor(s)/catalytic converter. Any reasonably recent car in good condition should be able to achieve these levels without any other extra gadgets.

CO2 levels are basically in inverse proportion to mpg; so light cars with smallish efficient engines tend to have lower figures than heavy cars with more powerful, and/or less efficient engines.

Hey Freedom thanks for the reply.

But if this device also gained me approximately 10% better mpg (which it does) then I got a chance of lowering the tax bracket it seems..

F

141-150

£135.00

G

151-165

£170.00

H

166-175

£195.00

If I take the garage's advice that the test is about as much as an MOT then it'd be two years before it becomes worth it... not sure I can be doing with that

Miraculous MPG improving and Co2 device = oh dear...

The garage haven't MOT'd many MPI's then as your readings aren't much different to my car (2001 8v 1.4 mpi). I get 41.x mpg over the last 8k and it's mechanically standard. What do you get with the 'device'? Are we talking hydrogen generation, resistor mods, magnetic fuel savers or a 12v fan wired up to the air box?

My MOT emissions results:

2011

Fast idle

CO: 0.0

HC: 2

Lambda: 1.006

Natural idle

CO: 0.01

2012

Fast idle

CO: 0.2

HC: 14

Lambda: 1.009

Natural idle

Co: 0.00

So unless you're getting a calculated (not the trip computer guesstimate) 45mpg+ over several tanks your 'device' appears to be doing nothing for you based on the emissions. I'm of course happy to be proved wrong

My last car was 1g of CO2 above the lower tax bracket, problem being that figure was calculated using a car with widest wheels/highest tune/all the options, my car started life with 20hp less, a standard exhaust and many of those options missing, still doesn't make any difference, it's a worst case figure.