de-catting a diesel

ralph · Post by **ralph** » 29 Aug 2005, 02:52

This is a topic we've discussed several times on the forum, but it seems taking the catalytic converter off an XUD diesel could cause a car to fail an MoT in the UK.
I've been told by an MoT station that the problem is this:
During this year, all MoT stations are going 'on line' whereby the MoT tester is linked directly to the DVLA by computer. Car comes in for a test, and the tester enters the car's number plate into his computer. Records show whether the car left the factory with a cat. If it did, the emissions test will be tougher, and demand lower pollution levels than for a car that never had a cat.
My exhaust on my Xsara had rusted through just behind the cat, and so I was trying to get a garage to remove the cat and fit a through pipe, as XUD motors had before the late 90s. This, I thought, would save me money and release a few BHP. The garage I used was happy to 'bypass' the cat, but I was told I'd never get it through the MoT.
Does anyone know if what I've been told is right??
(Luckily for me, the garage boss passed my car on to his new Latvian mechanic, who mustn't have understood the request for a 'de-cat'. In true communist style, he got out the welder and repaired it.)

Stinkwheel · Post by **Stinkwheel** » 29 Aug 2005, 03:04

When exactly did Cats come in as compulsory.
As i understand it all cars after about K reg must have a cat as standard.
Having said that, my wife owns a nissan, its a laye 93 L reg. Its not got a cat, its certainly never had one either, no sign of lambda wiring etc. (i assume diesel cats have lambda sensrs etc)
The standard exhaust for this model year doesnt have a Car either.

adamskibx · Post by **adamskibx** » 29 Aug 2005, 05:05

It was 1992 adn after that cars had to have one fitted but I dont know about deisels as mine is a K reg and does not have one.

nick · Post by **nick** » 29 Aug 2005, 05:43

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by ralph

I've been told by an MoT station that the problem is this:
During this year, all MoT stations are going 'on line' whereby the MoT tester is linked directly to the DVLA by computer. Car comes in for a test, and the tester enters the car's number plate into his computer. Records show whether the car left the factory with a cat. If it did, the emissions test will be tougher, and demand lower pollution levels than for a car that never had a cat.
<hr height="1" noshade id="quote"></blockquote id="quote">
This will certainly be the case for petrol vehicles, and I expect it could well be introduced for Euro IV diesels at some point in the future, but as far as I know there are no plans to introduce a tougher test for late '90s cat-equiped diesels at this stage.

ralph · Post by **ralph** » 30 Aug 2005, 16:07

Nick - it seems even garages that MoT test don't really know what's going on. I phoned three exhaust centres before gettng the repair, two which were MoT testing stations, and they all told me I 'might' struggle to get it through an emissions test, even though I had told them exactly what the car and its engine was.
By the way, the cost of a de-cat was £45, compared to around £230 for a new cat.

bxbodger · Post by **bxbodger** » 30 Aug 2005, 16:50

All a diesel has to pass is a fairly basic smoke test, which is not the same as a petrol emissions test.
A petrol test checks whats in the emissions, but all a smoke test does is test the density of the emissions- its not the same thing. Technically, a cat is NOT a legal requirement for any car,petrol or diesel, although a lot of testers seem to think it is, but in practice no-one has been able to develop a technology to get a petrol engine through current emissions testing without using a cat.
Its different for diesels- the smoke test is pretty simplistic and archaic, and comes from the days when there was no such thing as a cat for a diesel, and no other technology than a fuelling level screw!!
Its a pretty crude test and wether or not you have a cat will make no difference.
The test may be changed in the future to catch up with the new cleaner diesel emission technologies, but it won't be retrospective, so you have no problem with removing the cat from a diesel!!!
It will be the same as decatted pre 92 petrol cars that originally had a cat- thet don't have to pass the post 92 emission test, much the same as my 68 Vitesse does not have to meet post 75 C.O. levels.

DarkendViper · Post by **DarkendViper** » 30 Aug 2005, 18:02

I decatted my Xantia 1.9TD Estate and it went through the test easily. I did give it a run through the country to get it nice and warm. This was on a 96 model. A lot of places told me that it might not pass but I took the chance and it paid off.

Kowalski · Post by **Kowalski** » 30 Aug 2005, 20:43

If your diesel is too smoky to pass the smoke test without a catalyst, the cat will be so coated with soot/tar from the exhaust and will do absolutely nothing at all, so it wouldn't pass with the cat.

nick · Post by **nick** » 31 Aug 2005, 01:43

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by ralph

Nick - it seems even garages that MoT test don't really know what's going on. I phoned three exhaust centres before gettng the repair, two which were MoT testing stations, and they all told me I 'might' struggle to get it through an emissions test, even though I had told them exactly what the car and its engine was.
<hr height="1" noshade id="quote"></blockquote id="quote">
As I understand it, the computerisation of the MOT system only really affects the admin side. In general the test will still be carried out in the same way and with the same limits for emissions etc.
It will automatically be able to download from a database the emission limits applicable to a particular car, but for non-cat petrol cars registered in 1992-93 this had to be checked manually anyway.
There is no MOT requirement for any car to be fitted with a cat as such, the tester does not have to check for the presence or absence of one, merely that the emissions are within the applicable limits for the vehicle. The limits for diesel engines are set solely on the particulate emissions, which the cat makes no difference to.
It is possible that more stringent limits will be set for the current generation of cleaner diesels when they get old enough to need an MOT, but if there were any plans to introduce a tougher test for older diesels by the end of this year it would have been publicised and testers made aware of it by now.
Incidently, I was told that the UK government and the DVLA have no record of which older diesels are supposed to have a cat anyway. I don't know how reliable the source of this information is though!
I've experimented a bit on Citroen PR net, putting in the details of various different 1.9 atmo & turbo diesel Xantias, and it lists a cat for ALL of them going right back to 1993, regardless of whether they would have been fitted with one originally.
I wonder then, if even Citroen don't know which models are supposed to have one & which aren't ?!

madasafish · Post by **madasafish** » 31 Aug 2005, 02:55

6. Your vehicle has had its catalytic converter removed and replaced by a normal exhaust silencer but passes the emissions Test. Does it fail the MOT because it hasn't got a catalytic converter when it should have one?
a) No, if it passes the emissions part of the MOT that is acceptable.
http://www.motester.co.uk/motquizans.html

Kowalski · Post by **Kowalski** » 31 Aug 2005, 04:09

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by nick
I've experimented a bit on Citroen PR net, putting in the details of various different 1.9 atmo & turbo diesel Xantias, and it lists a cat for ALL of them going right back to 1993, regardless of whether they would have been fitted with one originally.
I wonder then, if even Citroen don't know which models are supposed to have one & which aren't ?!
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I always found Citroen PR net very good. If you put the VIN of any particular car in it finds the details of everything that car has fitted. If you change the engine type, you're modifying just THAT detail in the profile, i.e. you could tell PR.net that the car has options that are incompatable with one another and it just accepts them.
The way car production lines are computerised, a car can be specced differently from the ones before and after it on the production line, and the different parts are delivered specificially for it just in time. Nissan had radio transponders on their cars as they go down the line so the computer knows where a chasssis is and can order the parts and get the automated delivery systems to deliver them to the production line as they're needed, I'd assume Citroen has similar systems. If I were Citroen, I'd be using that production line order information to build the configurations on PR.Net.

nick · Post by **nick** » 31 Aug 2005, 05:03

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Kowalski
I always found Citroen PR net very good. If you put the VIN of any particular car in it finds the details of everything that car has fitted. If you change the engine type, you're modifying just THAT detail in the profile, i.e. you could tell PR.net that the car has options that are incompatable with one another and it just accepts them.
<hr height="1" noshade id="quote"></blockquote id="quote">
Yes, with a VIN its spot on. Trouble is I only had a couple of VINs to try and without a VIN its quite possible to choose combinations that could never exist, (eg it'll quite happily specify parts for a Xantia 1.6i V6 diesel auto estate [:D])
What I tried to do was put in the bare minimum details, such as 1.9D base manual saloon, and it still came up with the part no of a catalyst even for that. Maybe either that model did have a cat in some countries, or it just tries a sort of "best guess" if you select a part thats not normally fitted?