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Decat on TDi - Fail MOT?
- Thread starter trebormint
- Start date
brad1
Guest
They are talking b0llocks, ive got straight through, no cat or back box and mine passed a mot fine 
dont need cat for mot on a derv , they dont check emmissions , just the soot levels or so i was told
In England you can drive, pass an MOT, have an accident and do what the hell you like with the CAT removed from a diesel car and it is all legal. It is different in other countries like all other laws are differnt but in England you have no worries.
Not true, Its any car newer than a certain date requires a cat.
The date itself escapes me however this is the case.
^^
Information provided by an ex officer of the law
Not true - he's lying if he's referring to MOT it might be true at point of production but on a diesel it is NOT an MOT requirement as none of the emissions tests they do test any emission that is affected by a Catalytic Converter.
Visual smoke test and C02 test only - that's it. Mine has sailed through 2 MOTs now and that's with the tester noticing the exhaust each time, with no silencers and no Cat it's not like you can miss that it's not standard.
The Cat on our cars is not active, it's passive and as such has no input to the engine management system, all it functions as is a glorified soot catcher - mine actually runs better and smokes less without the stupid thing. To be entirely honest, Cats only work in countries where the exhaust temperatures are high enough to activate the material inside the Cat - short journeys in the UK will never achieve that temperature and as such .... most of the time having a catalytic converter is pointless.
Source here.
No catalytic converter test for diesel engined vehicles.
However, "The MOT Inspection Manual" states: -
Source here.
Now you can take that any way you choose. Either the exhaust must be complete and as designed from the factory (including the cat) or that the exhaust must be complete with no part missing (a complete exhaust rather than one which has a section such as the tail pipe not present).
As my MOT station removed the cat on my van earlier this year when it corroded, and fitted a straight through pipe instead, then I'm inclined to think that come MOT time it's going to pass.
Now more confused!
Seems that you could pass the MOT if it passes the smoke test and CO2 test.
But could fail if the examiner notices it doesn't have a CAT when it should???
Seems that you could pass the MOT if it passes the smoke test and CO2 test.
But could fail if the examiner notices it doesn't have a CAT when it should???
Now more confused!
Seems that you could pass the MOT if it passes the smoke test and CO2 test.
But could fail if the examiner notices it doesn't have a CAT when it should???
yes and if unlucky to get a sharp-eyed and bad day having tester then yes it could fail on a technicality
although not 100% by any means the suggestion of it being broken on a speed hump and the pipe is a repair usually will get you by if you keep it polite
for you big blowers watch yaselves UncleFester wrote
The Cat on our cars is not active, it's passive and as such has no input to the engine management system, all it functions as is a glorified soot catcher - mine actually runs better and smokes less without the stupid thing.
Sorry, but that's not right.
A catalyst increases the rate at which a chemical reaction take place without actually being involved in the reaction.
In a petrol car, the catalyst promotes the decomposition of three pollutants:
http://auto.howstuffworks.com/question66.htm
http://www.answers.com/topic/catalytic-converter
http://www.eurocats.co.uk/technical.php
The catalyst does not filter out particles. If it did, it would soon clog up and stop your engine from running.
Diesels produce less pollutant gases, as the engine cycle is more efficient and diesels are almost always running lean, so there is plenty of oxygen present to ensure complete combustion. To meet emission reglations, diesels use a simpler two-way oxidation catalyst which doesn't affect NOx. NOx is controlled in the TDI engine by EGR.
In a petrol car, the oxygen content of the exhaust is monitored by the ecu at points before and after the catalyst, and the petrol-air mixture is adjusted to ensure that the correct proportion of oxygen remains in the exhaust gas for the balance of oxidation reactions and reduction to be maintained.
To be entirely honest, Cats only work in countries where the exhaust temperatures are high enough to activate the material inside the Cat - short journeys in the UK will never achieve that temperature and as such .... most of the time having a catalytic converter is pointless.
Exhaust temperature is only trivially dependent on outside air temperature, and the catalyst is warmed by the reactions taking place inside it, the ones that it catalyses. That's why some petrol cars have secondary air pumps, to pump extra clean air into the exhaust so the catalyst has oxygen to work with to burn up the hydrocarbon and CO produced at startup. The catalyst itself is working all the time, hot or not.
The Cat on our cars is not active, it's passive and as such has no input to the engine management system, all it functions as is a glorified soot catcher - mine actually runs better and smokes less without the stupid thing.
Sorry, but that's not right.
A catalyst increases the rate at which a chemical reaction take place without actually being involved in the reaction.
In a petrol car, the catalyst promotes the decomposition of three pollutants:
- Hydrocarbons (HC) i.e. unburnt fuel. Become water (H20) and carbon dioxide (CO2)
- Carbon monoxide (CO) from incomplete combustion. Becomes carbon dioxide.
- Nitrous oxides (NOx) produced at high combustion temperatures. Becomes nitrogen (N2) and Oxygen (O2)
http://auto.howstuffworks.com/question66.htm
http://www.answers.com/topic/catalytic-converter
http://www.eurocats.co.uk/technical.php
The catalyst does not filter out particles. If it did, it would soon clog up and stop your engine from running.
Diesels produce less pollutant gases, as the engine cycle is more efficient and diesels are almost always running lean, so there is plenty of oxygen present to ensure complete combustion. To meet emission reglations, diesels use a simpler two-way oxidation catalyst which doesn't affect NOx. NOx is controlled in the TDI engine by EGR.
In a petrol car, the oxygen content of the exhaust is monitored by the ecu at points before and after the catalyst, and the petrol-air mixture is adjusted to ensure that the correct proportion of oxygen remains in the exhaust gas for the balance of oxidation reactions and reduction to be maintained.
To be entirely honest, Cats only work in countries where the exhaust temperatures are high enough to activate the material inside the Cat - short journeys in the UK will never achieve that temperature and as such .... most of the time having a catalytic converter is pointless.
Exhaust temperature is only trivially dependent on outside air temperature, and the catalyst is warmed by the reactions taking place inside it, the ones that it catalyses. That's why some petrol cars have secondary air pumps, to pump extra clean air into the exhaust so the catalyst has oxygen to work with to burn up the hydrocarbon and CO produced at startup. The catalyst itself is working all the time, hot or not.
You know far too much about this for your own good - i just know the cat came from california and that's definitey hotter than here
TThat said on a short trip ( say a 5 mile commute) you're never going to get EGT high enough for the cat to work effectively, perhaps i should have been more specific.
By active / passive, i meant that what goes on in a diesel cat is not measured by the cars ECU and as such has no overall effect on the engine mamagement or how it runs.
TThat said on a short trip ( say a 5 mile commute) you're never going to get EGT high enough for the cat to work effectively, perhaps i should have been more specific.
By active / passive, i meant that what goes on in a diesel cat is not measured by the cars ECU and as such has no overall effect on the engine mamagement or how it runs.
A diesel car does not require a Cat to pass the MOT, as as only a smoke test is carried out.
Infact a petrol car doesn't actually need a cat to pass the MOT, so long as it passes the BET test, some modern engines, that are running correctly, are clean enough to go through the BET test without the need for a Cat.
The Cat itself isnt part of the test, its just the gases that are produced from the car that are tested. (other than excessive blowing, excessive noise and excessive corrosion that is)
Infact a petrol car doesn't actually need a cat to pass the MOT, so long as it passes the BET test, some modern engines, that are running correctly, are clean enough to go through the BET test without the need for a Cat.
The Cat itself isnt part of the test, its just the gases that are produced from the car that are tested. (other than excessive blowing, excessive noise and excessive corrosion that is)
So basically it breaks down like this.
In order to pass the tests all cars are subject to, it will pass with flying colours all TDI's will.
HOWEVER
If your pulled over by a particuarly arsey police man he CAN fine you for it and take your car off the road.
or
If your MOT'er decides he wants to make some extra money he CAN say your car isnt road legal.
Basically, if you know someone whos pretty good and does MOT's or people who are lazy, Just do it.
The police PROBABLY wont notice, their inspections are normally of the tyres, washer jets etc.
and an MOT'er PROBABLY wont fail you for it.
The chances are always there however.
In order to pass the tests all cars are subject to, it will pass with flying colours all TDI's will.
HOWEVER
If your pulled over by a particuarly arsey police man he CAN fine you for it and take your car off the road.
or
If your MOT'er decides he wants to make some extra money he CAN say your car isnt road legal.
Basically, if you know someone whos pretty good and does MOT's or people who are lazy, Just do it.
The police PROBABLY wont notice, their inspections are normally of the tyres, washer jets etc.
and an MOT'er PROBABLY wont fail you for it.
The chances are always there however.
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