LPG and MOT Emissions test

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JD

JD

New Member
Posts
161
Location
South Wales
Hey folks,

Quick question about MOT emissions testing for an MOT.
Was expecting it to fly through being on LPG but it struggled to pass, was originally reading about 1% CO and between 300 and 500 on the HC.

After a bit of reading it looks like the tester should have put it on the analyser as a non-cat vehicle due to the LPG so the limits are quite a bit higher (3% and 1200?)

Anyone able to confirm this?
 
As far as I see it, the vehicle is tested on the fuel system is was driven to the MOT station on...

If the vehicle as standard had a CAT from the factory, regardless of fuel system fitted, it gets tested as such.

LPG does have a cleaner CO output but usually the Hydro-Carbons are elevated, this is just due to the burn characteristics of LPG against Petrol....but it should still not be high enough to fail...might be time to have the LPG system serviced!

EDIT:
Vehicles which run on more than one fuel(e.g. petrol and LPG) should be tested on the fuel they are running on when presented. There is a slight difficulty with LPG vehicles: the hydrocarbons emitted are propane rather than hexane. So the HC reading obtained must be divided by the “propane/hexane equivalency factor” (PEF) marked on the gas analyser. For example: An LPG vehicle gives a reading of 700 ppm. The PEF marked on the machine is 0.48. So the actual MOT value is: 700 0.48 = 1458 i.e. fail

Some exhaust gas analysers have an automatic facility for doing this
Click to expand...
 
Last edited:
readings on a recently passed LPG V8 petrol were as follows:

at 2500-3000 RPM
CO: 0.10 (limit is 0.20%)
HC: 20 (limit is 200 ppm)

at idle (up to 1500 rpm)

CO: 0.03 (limit is 0.30%)


hope this helps.
 
Last edited:
Thanks for the replies guys.
Have done less than 10k on gas but it runs very well, will have to look into it some more.

@saintV8 - I saw that page previously...but saw this as well:
http://www.motuk.co.uk/images/non_cat.pdf
Though like you said if it has cats as standard that's how it gets tested.

@dolphinboy - Those readings are well under the limits eh, I was wondering if this is down to the analyser and wether it adjusts automatically for the LPG or not.

Will have another look at the setup at some point and maybe head back to the garage for a quick chat about the analyser.
 
JD said:
Thanks for the replies guys.
Have done less than 10k on gas but it runs very well, will have to look into it some more.

@saintV8 - I saw that page previously...but saw this as well:
http://www.motuk.co.uk/images/non_cat.pdf
Though like you said if it has cats as standard that's how it gets tested.

@dolphinboy - Those readings are well under the limits eh, I was wondering if this is down to the analyser and wether it adjusts automatically for the LPG or not.

Will have another look at the setup at some point and maybe head back to the garage for a quick chat about the analyser.
Click to expand...
The issue date of that PDF extract was June 2010...MOT Rules changed since then!
 
If your vehicle was manufactured in or after 1992 is has a full cat test as i understand it. However it can be tested on the fuel it is present on if it is dual fuel. Calculations are then done to arrive at the generated emissions. The vehicle VIN number will dictate which test is required. Unless you have fitted an earlier engine, then it is tested on the regulations and limits applicable at time of engine manufacture. In which case you have to show documented proof. A change was made in 2012 that even if a car presented on LPG is tested on LPG and passes it MUST have a cat fitted if one was fitted as standard. Many removed cats then presented on LPG. Can't be done any longer.
 
Last edited:
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