Is a cat necessary for LPG equiped cars?

[marco]

Just a thought, if I run my volvo on lpg all the time can I ditch the cat, as it sometimes smells on short runs. I guess it would pass emmisions fine on lpg without a cat but what is the legal position?

[junkcatcher]

If the car has a down stream lambda sensor it is almost certain to trigger a fault code.
The engine ECU uses the downstream sensor to check if the cat is working.

[tommo2009]

anything after 1992 (i think) must have a cat regardless of wether it is on LPG or not.

[bxman]

I have been thinking on the same lines particularly as efficiency and hence economy would be improved with a plain pipe in place of the cat wouldn't it ?

[marco]

If the car has a down stream lambda sensor it is almost certain to trigger a fault code.
The engine ECU uses the downstream sensor to check if the cat is working.

It's only got a sensor 'pre-cat' as it's a earlyish vehicle.

[martin rowe]

LPG vehicles do not have a 'catalyst' emission test for MOT, so a cat is not required for MOT.

[tommo2009]

get in touch with your local MOT station, anything after 1992 must have a cat regardless of wether it is on LPG or not that is the law.

[martin rowe]

The fitment of a 'cat' or not is not part of an MOT examination, the only thing is the vehicle has to pass the relivant emission test, whish 1993 on is a cat test, only exception is an LPG equiped vehicle, it has a basic 'non cat' emission test for MOT. take that from an Authorised Examiner, a Nominated Tester & a Quality Controler, oh and MOT staton owner.

[marco]

Thanks Martin, that's very helpful information.
So in theory if you could get the emmissions down a 'non-cat' car could pass the mot, although I guess in practice it's not possible on petrol.

[martin rowe]

No an LPG car will not pass 'cat' emissions when running on LPG, but an LPG car dose'nt have a 'cat' emission test for MOT, just the old 'non cat' test ie, CO less than 3.5%, HC less than 1200ppm, and it makes no differance weather its a brand new manefacturer supplies car or a 10 yr old self converted one, just make sure the 'LPG' fuel tab is selected on the MOT computer, the system then tells the MOT tester which type of emission test to perform. This is all because VOSA have not had emission limits developed for LPG vehicles.

[martinpluss]

Do you know where I can find an official vosa document that confirms that an LPG car doesn't have a 'cat' emission test? I'm trying to prove this to my tester... My lpg converted 97 range rover has a cat and he is insisting on doing a cat test...

[kevintourer]

Do you know where I can find an official vosa document that confirms that an LPG car doesn't have a 'cat' emission test? I'm trying to prove this to my tester... My lpg converted 97 range rover has a cat and he is insisting on doing a cat test...

change your mot testing stn, mine always ask which I would like it tested on.

[mat_fenwick]

No an LPG car will not pass 'cat' emissions when running on LPG

I've found that it can in my experience - admittedly just the once but I put a 1994 Discovery V8 through the MOT where the (expensive to replace) cats had been replaced by steel tubes. I explained the situation and they told me the vehicle should be tested on the fuel it was running on when it arrived (in this case LPG) and it passed.

Whether all LPG cars will pass an MOT without a cat fitted is a different question though...

[Gilbertd]

Unless there is something wrong with them and the fuelling is incorrect, they all will. If presented for test running on gas, whether cats are fitted or not is irrelevant (the compulsory fitment is a type approval issue, not an MoT testable one) and it will be tested to the appropriate standard. See http://www.motuk.co.uk/images/non_cat.pdf.

The only tests in the MoT regarding the exhaust system, is does it leak, is it secure, is the noise level not excessive? See http://www.motuk.co.uk/manual_710.htm

[pjpj]

Just for interests sake, does removing the cat. improve economy any?
And, would the post cat. lambda sensor detect there was no cat. whilst running on LPG? Does running on LPG still produce too much Nitrogen and Nitrogen Oxides etc.

[junkcatcher]

Definite Fail

Reasons for failure: Exhaust
a. [b] A part of the system missing [/b] or excessively deteriorated

To me that means the exhaust system must be complete ---- to me that means you can't just throw bits away because you don't like them.

[Gilbertd]

Junkcatcher, taking your logic any car with a non-standard exhaust of any type would immediately fail as parts are missing (in some cases the whole system). So replacing the tailpipe box with an aftermarket one would be an immediate fail as would replacing it with a straight length of pipe. I think you'll find that unless you get an extremely pedantic tester (and you could appeal the fail anyway and I suspect you would win), parts missing means that the tailpipe has dropped off or similar. Actually checking for the presence of a cat isn't in the test, neither for that matter is checking that it has the same number of silencer boxes that it had when it came out of the factory.