De-cat on tdi's

ashb 130 tdi

Active Member
Jun 11, 2009
31
0
Notts
Had mine done last year, full system with cat and back box removed. No problems at all to report and passed MOT fine. It revs alot better, seems quicker than it was before, doesn't smoke anymore than it used to and sounds awesome! Would defo recommend!!
 

gio

Guest
de cat wont be a problem for the mot test,since the emission test for diesels hasn't changed since 1986!

Did read somewhere on a vag site that decating a standard engine was unwise,and should only be done with a remap, but other diesel cars seem fine and some actually do give a few horses extra too.
 

Dieselman 73

Guest
Hi does anyone know if the de cat pipe from a Fabia VRS 1.9 Tdi will fit the Altea XL 1.9 Tdi? I know when it was fitted to the Fabia the differance it made was significant. I am also thinking of trying the chip fom the Fabia. I know when we set it to setting '8' the Fabia would keep up with a Cupra R but the clutch could not hold the power. It started slipping about 2500 revs. Been Ok on lower chip setting.
 

[RPM]

Active Member
Jun 9, 2009
7
0
In my opinon the biggest gain you will get from a decat will be the
EGT's going down.
and giving a longer life to the turbo.
especially in modified cars
 

spud31

Rail Zip User
Jul 14, 2011
407
2
Guys just to add some info, my mk4 fr TDI had MOT yesterday, and has full Miltek system including the decat downpipe EGR blanked and poss usual boost leak.
Smoke test limit is now 1.50 and mine passed not fully warm at 1.17.
A Passat PD TDI being tested at same time with standard exhaust and cat came in at 1.

So all good
 

epts2008

rule the bends
Mar 19, 2009
281
1
Chelmsford, Essex
Being an mot tester I can tell you that diesel cars do not have a catalytic converter everyone calls them a cat but it is infact just a smoke box to collect soot.
 

Muttley

Catch that diesel!
Mar 17, 2006
4,987
31
North Kent
I'm afraid that diesels do have catalytic converters. They are not as complicated as those on petrol cars, but nevertheless they are still catalytic converters. Diesels are required to have a two-way catalytic converter that catalyses the oxidation of partially burned hydrocarbons (CHx) and carbon monoxide (CO) into water (H2O) and carbon dioxide (CO2). Diesels always have plenty of excess oxygen in the exhaust (except at full throttle, but then there is almost nothing to catalyse).

Because there is no need to tune the fuel injection to ensure excess oxygen in the exhaust, there is no need for lambda probes, which measure the oxygen content in petrol car exhausts.

In the last few years, diesels have also had to have Diesel Particulate Filters installed. These could be viewed as a box to collect soot, although it is a bit more complicated than that. This is in addition to the catalytic converter.
 

john_tdi

mmm 385lbft
Feb 21, 2007
687
0
s wales
god sake, this debate still going? decats will pass the mot.. end of. smoke test only, and it would be pretty poorly to fail it too as the the car isnt even under load!

Just had my decat van mot'd and I've had a look at the new guides inspectors have. Friend of the family is a chief mot inspector for a council where I took said van. Loads of pointless things coming in this year, mainly electrical and light covers etc tints. No cat info.

Plus the new crap paper mot which is a joke.
 
god sake, this debate still going? decats will pass the mot.. end of. smoke test only, and it would be pretty poorly to fail it too as the the car isnt even under load!

Just had my decat van mot'd and I've had a look at the new guides inspectors have. Friend of the family is a chief mot inspector for a council where I took said van. Loads of pointless things coming in this year, mainly electrical and light covers etc tints. No cat info.

Plus the new crap paper mot which is a joke.

the mot tester yesterday told me the cat bit comes in in may just a visual inspection and if your car is meant to have one and its been removed and they see its not there then its a fail
 

john_tdi

mmm 385lbft
Feb 21, 2007
687
0
s wales
the mot tester yesterday told me the cat bit comes in in may just a visual inspection and if your car is meant to have one and its been removed and they see its not there then its a fail

then he's been given the wrong advice then simples...

I've seen and spoke to the chief mot inspector for my local council.

He doesn't run a garage, nor work for one. So its no skin off his nose if you fail or pass. He only fixes council vehicles.

They mot a very small amount of private vehicles and mostly mot taxis etc.

like I said before, changes are coming in like dash error lights, tow bar electrics, and tints applied to headlights, nothing for cats.
 
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then he's been given the wrong advice then simples...

I've seen and spoke to the chief mot inspector for my local council.

He doesn't run a garage, nor work for one. So its no skin off his nose if you fail or pass. He only fixes council vehicles.

They mot a very small amount of private vehicles and mostly mot taxis etc.

like I said before, changes are coming in like dash error lights, tow bar electrics, and tints applied to headlights, nothing for cats.

he had it on a sheet from vosa stuck to the wall in the mot bay with all the dash warning lights and tow bar electrics etc info on it as well
 

john_tdi

mmm 385lbft
Feb 21, 2007
687
0
s wales
Below is the actual revised quote from the 2012 MOT testers manual, its syntax is detached because it comes under the column heading of "Method of inspection"

So the statement would read

Method of inspection
Quote:
3.On vehicles that qualify for a full cat emissions test, check the presence of the catalytic converter.

It seems quite clear that the presence of a cat will only be required on vehicles requiring a "full cat emissions test" and because diesels only require a smoke test, a cat would not need to be present.

That said I wouldnt be supprised some garages failing diesels that didnt have them, as they don't understand the rule!
 
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AJ FR

Guest
you will pass your mot with decat do not worry my brother

decat will make the turb spool up a little quicker and you will notice a little quicker on revs building up
 
Below is the actual revised quote from the 2012 MOT testers manual, its syntax is detached because it comes under the column heading of "Method of inspection"

So the statement would read

Method of inspection
Quote:
3.On vehicles that qualify for a full cat emissions test, check the presence of the catalytic converter.

It seems quite clear that the presence of a cat will only be required on vehicles requiring a "full cat emissions test" and because diesels only require a smoke test, a cat would not need to be present.

That said I wouldnt be supprised some garages failing diesels that didnt have them, as they don't understand the rule!

so at that then the guy that did my mot doesnt understand what it means then