What exactly is the law regarding catalytic converters?
Discussion
As a result of a tangent on the DPF\MOT thread I started rambling on about catalytic convertors, and not wanting to derail that thread further thought I'd start a new one.
As I understood it, upto 2012, at MOT time:
but there was nothing in the law mandating a cat for any car, just the reality that it was extremely difficult to pass the stricter emssions test without one.
Relatively recently the MOT rules changed such that if a car "was required to have a cat when it was built", the cat must be present at MOT time (even if the car can now pass the emssions test without it).
Firstly us that understanding right?
And if so where does the 'requirement' to have a cat come from? Can anyone point me to the relevant piece of legislation?
As I understood it, upto 2012, at MOT time:
- cars registered prior to 1st August 1993 must pass one of two emissions tests, one for cars without cats, and a stricter one for cars with cats.
- cars registered on or after 1st August 1993 must pass the stricter of the two tests above
but there was nothing in the law mandating a cat for any car, just the reality that it was extremely difficult to pass the stricter emssions test without one.
Relatively recently the MOT rules changed such that if a car "was required to have a cat when it was built", the cat must be present at MOT time (even if the car can now pass the emssions test without it).
Firstly us that understanding right?
And if so where does the 'requirement' to have a cat come from? Can anyone point me to the relevant piece of legislation?
It's a grey area - or at least it was.
Up to K-Reg cars could be eligible for a non-cat emissions test. Effectively anything goes in one of those. After K-Reg (1993) new cars had to pass a cat emissions test. This was to ensure we adhered to EEC-III regulations. It was a long time ago!
It gets a little complex as some dealers had unregistered stock compliant with the old rules, they were given two registrations' grace to sell it thus some K and L reg cars are eligible for non-cat testing. It's dependent on engine number.
Additionally any non-UK market personal imports were also eligible up to the end of L-Reg, so 1993/4 Skylines and Imprezas get away with de-cats legally.
As for conversions, it's down to whichever is older. So if a non-cat car (pre K-Reg) is fitted with a later engine, no cat is required. Even though the engine would normally have a Cat and possess the systems to run one.
If a cat-equipped car is fitted with a non-cat engine then it will revert to the non-cat test regardless of the age of the car. It's weird but people do it.
This goes for three way catalysts on petrol engines. Prior to EEC-III some cars, especially American, had two way cats. These are much more primitive, and wreck power output. They can, however, work without Lambda sensors and fuel injection. Most older engines are dirty enough to destroy a three way cat. Any car with one of those would be non-cat tested, so they can be removed.
Diesels also have a two-way cat; which have never been mandatory up until now as they don't have any effect on the smoke density test.
Thus we have cat-tests and non-cat tests. There was nothing in the regs to say a cat had to be fitted, only that the car should pass the test. Some cars with small or particularly clean engines were more than capable. I remember my old Nissan Bluebird, both carburettor fed and non-cat, would easily have passed a cat-test. The standards are really quite low! A visual check was never required, maybe that's changed?
Up to K-Reg cars could be eligible for a non-cat emissions test. Effectively anything goes in one of those. After K-Reg (1993) new cars had to pass a cat emissions test. This was to ensure we adhered to EEC-III regulations. It was a long time ago!
It gets a little complex as some dealers had unregistered stock compliant with the old rules, they were given two registrations' grace to sell it thus some K and L reg cars are eligible for non-cat testing. It's dependent on engine number.
Additionally any non-UK market personal imports were also eligible up to the end of L-Reg, so 1993/4 Skylines and Imprezas get away with de-cats legally.
As for conversions, it's down to whichever is older. So if a non-cat car (pre K-Reg) is fitted with a later engine, no cat is required. Even though the engine would normally have a Cat and possess the systems to run one.
If a cat-equipped car is fitted with a non-cat engine then it will revert to the non-cat test regardless of the age of the car. It's weird but people do it.
This goes for three way catalysts on petrol engines. Prior to EEC-III some cars, especially American, had two way cats. These are much more primitive, and wreck power output. They can, however, work without Lambda sensors and fuel injection. Most older engines are dirty enough to destroy a three way cat. Any car with one of those would be non-cat tested, so they can be removed.
Diesels also have a two-way cat; which have never been mandatory up until now as they don't have any effect on the smoke density test.
Thus we have cat-tests and non-cat tests. There was nothing in the regs to say a cat had to be fitted, only that the car should pass the test. Some cars with small or particularly clean engines were more than capable. I remember my old Nissan Bluebird, both carburettor fed and non-cat, would easily have passed a cat-test. The standards are really quite low! A visual check was never required, maybe that's changed?
digger the goat said:
Nice answer thanks..
One question though... Does that mean that an older diesel with a 'cat' can be 'de-catted' with no future probs at mot time ??...say, a 1999 V70 2.5d ?
I don't know what the newest requirements are. Up to last year it would have been fine, the old diesel test was only for smoke output which the cat doesn't effect. De-catting diesels is done but isn't as common as with petrols. I don't think it actually makes much difference to diesel engines so the expense involved with having a de-cat section made probably outweighs the benefits. If it's a turbo diesel it might spool up a bit faster owing to less back pressure. One question though... Does that mean that an older diesel with a 'cat' can be 'de-catted' with no future probs at mot time ??...say, a 1999 V70 2.5d ?
Edited by Futuramic on Sunday 15th December 20:38
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