discool said:

Correct! 'unless' they can pass without a cat, so nothing has changed for these vehicles in the 2012 MOT regs. but 2002 vehicles have to have a cat fitted for the MOT test even though the may have passed without it.
That's the difference

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Yeah exactly that, I didnt add that bit but post 2002 need to be as the manufacturers made them, also diesels dont need to have a cat at all as long as they past a smoke test. EGR systems dont come into either petrol or diesel testing, there may be a manafacturers rule (i.e. to be produced they must have one fitted) but its not an MOT item...

andyt54 said:

hi all just wondering if a 91 exhaust system with out the cats would fit on my 95 v8, my cats are gone and just been informed im looking at £400 ish, cheers Andy

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I assume you don't have LPG fitted. I present mine for MOT running on LPG.

yes to the above, i have a twin tank lpg fitted.....

I run mine on LPG too so no probs with the emissions test, The proper one will cost you £400 but you can actually pick up a Y pipe with cats new off ebay for £200, much lighter steel but you pay for what you get.

You could just go round a few test centers and ask them if they will fail it for no cats, maybe they should (on emissions but running on LPG you should be ok) but in reality some dont actually care (Ive heard tales of testers plugging the emmisions tester onto a different vehicle whilst doing your test), if they dont care you could go to them but you must ask yourself if they dont care about that what else are they turning a blind eye to? Too much emissions is one thing, an unsafe motor is another.

Another option maybe: cut open the cat boxes, remove the insides and weld back up, it'll still look like cats.

my mate said he would pass it with cats or without, is a de cat straight forward?

well there you go then sorted.

I havent done it myself I bought the cheapies (gonna bite the bullet one day and buy the front half of my stainless Janspeed system when I can afford it, currently its a cat back system).

Presumably it would involve cutting the cats out with the exhaust still attached (if poss), tacking pipe in place, then removing the y pipe and welding around the joins to seal it. The bolts attaching it to the manifold often shear off and that can be a bit of a bitch of a job.

ok thanks for that, i will def look into it

This is a flowchart from the current MOT manual. http://www.motuk.co.uk/images/730_newp9.pdf. If the Vehicle was first used after 1 August 2005, or they have the exact vehicle data in the analyser database, (very likely on a common vehicle like a Discovery) then it will be subject to the CAT test, and will need a cat fitted.

Jongould said:

Yeah exactly that, I didnt add that bit but post 2002 need to be as the manufacturers made them, also diesels dont need to have a cat at all as long as they past a smoke test. EGR systems dont come into either petrol or diesel testing, there may be a manafacturers rule (i.e. to be produced they must have one fitted) but its not an MOT item...

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That's how I understood it! Stopped testing about four years ago so a bit rusty. But haven't they brought in some new regs this year on diesel cats? Basically if it left the factory with one they're meant to just do a visual check to see if it's fitted! It's still the same smoke test so it can just be an empty box?

Diesel Do said:

That's how I understood it! Stopped testing about four years ago so a bit rusty. But haven't they brought in some new regs this year on diesel cats? Basically if it left the factory with one they're meant to just do a visual check to see if it's fitted! It's still the same smoke test so it can just be an empty box?

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In the latest regs EGR systems are specifically mentioned and on diesel engines the lack of them should cause a fail.

Diesel Do said:

That's how I understood it! Stopped testing about four years ago so a bit rusty. But haven't they brought in some new regs this year on diesel cats? Basically if it left the factory with one they're meant to just do a visual check to see if it's fitted! It's still the same smoke test so it can just be an empty box?

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Its the opposite, a diesel doesnt need a cat at all, we have no reference for which vehicles have what, there are cats, DPF's, cleaner systems e.t.c

Basically if it passes then its fine, thats all that matters with diesels, most modern diesels we cant even get readings on so we have to abandon the gas test and do a visual check.

Jongould said:

Its the opposite, a diesel doesnt need a cat at all, we have no reference for which vehicles have what, there are cats, DPF's, cleaner systems e.t.c

Basically if it passes then its fine, thats all that matters with diesels, most modern diesels we cant even get readings on so we have to abandon the gas test and do a visual check.

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Looks like me misreading it
Found this.

Hi, I thought I would post this info up as there has been alot of talk regarding the new MOT rules and DPF removal. The following email came from VOSA and it states that the new MOT test on a diesel DOES NOT require a DPF or CAT to be fitted as long as it passes the smoke test you will pass.




Thank you for your e-mail reply dated 19th December 2011, concerning new MOT test rules.

The fitment of a catalytic converter to petrol engine vehicles is mandatory for vehicles of the specified age and type e.g. passenger car, goods etc. The MOT Inspection Manual can therefore specify exactly what petrol engine vehicles must have a catalyst fitted.

However, whilst diesel engine vehicles are required to meet certain emissions limits for Type Approval, the method used to achieve this is not specified. It was left to the engine manufacturer to decide how to meet Euro 3, 4, 5 etc emissions standards.

For this reason, testers would be unable to readily determine which vehicles are OE fitted with a Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF) or Selective Catalytic Reduction (SCR) system.

It was therefore considered that the introduction of a Reason for Rejection for a missing diesel catalyst at this stage, whilst complying with the Directive, was likely to lead to many incorrect failures, which is clearly unacceptable.

The matter is under review and may therefore change in the future.





Thank you for your e-mail reply dated 20th December 2011, concerning new MOT test rules.

VOSA have proposed an amendment to the Method of Inspection in the Inspection Manual, so that it will read "On petrol engine vehicles that qualify for a full cat emissions test, check the presence of the catalytic converter".

However, this amended wording will not find its way into the Manual until the new testable components become failable in the spring.


Ok to remove on diesels cos there's no way of policing it at the moment!
Thank god for that