how are exhaust emmisions checked?
23-03-2009, 07:35 AM
#1
how are exhaust emmisions checked?
i've just been having a think and i've found something else i can't quite get my head around (nothing unussual there i hear you say 
)
right then, this is what i think i know
you've got your basic mot emissions checks yes? which measure how much shite your engine is chucking out and if your cat is goosed or not on newer cars
then you have your carbon stuff that the government is taxing you on for road tax based on which band it's in
are either of these tests affected by the other?
why do some garages take different measurements? the one i go to has recently started to do a normal idel speed emissions test and then one at around 2500 rpm, if there is no load on the engine, will it make any difference?
is there a certain rev band that the tax based emmisions are taken from?
are they the best possible figures to get or would they vary across the rev and load ranges?
etc
thanks
)right then, this is what i think i know
you've got your basic mot emissions checks yes? which measure how much shite your engine is chucking out and if your cat is goosed or not on newer cars
then you have your carbon stuff that the government is taxing you on for road tax based on which band it's in
are either of these tests affected by the other?
why do some garages take different measurements? the one i go to has recently started to do a normal idel speed emissions test and then one at around 2500 rpm, if there is no load on the engine, will it make any difference?
is there a certain rev band that the tax based emmisions are taken from?
are they the best possible figures to get or would they vary across the rev and load ranges?
etc
thanks
23-03-2009, 07:54 AM
#2
20K+ Super Poster.
The reason they raise the revs to 2500 is to clear the exhaust system of previous pollutants, as most engines run far cleaner at 2500 than at idle, called purging, mostly necessary on all cars to pass the mot test emissions wise, that's why my tester will not do a test until the engine fan has come on then gone off, so it's basically to give it a fighting chance of passing.
tabetha
tabetha
23-03-2009, 07:55 AM
#3
They've not recently starting doing this....least I hope that's not the case...they should have always been doing it like this on cat test's.
www.motuk.co.uk
Readings are taking at idle and also at 'fast idle' on cats. Non cat tests receive a purge as tabetha says but then the actual reading is taken at idle.
www.motuk.co.uk
Readings are taking at idle and also at 'fast idle' on cats. Non cat tests receive a purge as tabetha says but then the actual reading is taken at idle.
Last edited by cossie604; 23-03-2009 at 07:57 AM.
23-03-2009, 08:59 AM
#4
he did it this year, and the year before, but not before that
but this would only give you a reading at idle and at part throttle, not under any sort of load where you would find stuff like pinking etc, so you oculd pass the emissions at the test station, yet fail them on a drive by road side test kit right?
and why do they vary so much? you can only injest a certain amount of fuel and air for each bang so the reading "should" be the same right?
but this would only give you a reading at idle and at part throttle, not under any sort of load where you would find stuff like pinking etc, so you oculd pass the emissions at the test station, yet fail them on a drive by road side test kit right?
and why do they vary so much? you can only injest a certain amount of fuel and air for each bang so the reading "should" be the same right?
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