De-Catting

Has anyone de-catted a fronty?

Ive got a bad feeling that my cat may have deteriorated in my multiple headgasket failures with all the oil and water blowwing through it.

The Cat went on my E36 BMW so i decatted it as a cheaper option and it all worked well.

Would it cause massive problems with sensors etc.?

Cars registered after 1st August 1992 require a cat to be fitted by law

if you can get emmissions down and they don't spot you dont have a cat you might get away with it but would it run right

Exhaust system

Test Description

The exhaust system will fail the MOT if:

Part of the system missing or excessively deteriorated
A mounting is missing or damaged so it does not support the system
There is a major leak
The system is excessively noisy.
Emissions

These are checked using specialised equipment, the details of the check depending on the year that the vehicle was first used on the road. Excessive smoking (checked visually) is a reason for failure.

Diesel smoke emissions are checked by using a smoke meter

http://www.motester.co.uk/mot-cog.html

Good posting there John,very useful to know the date involved :ggod post:

the car will run perfectly fine (if not better) without the cat :lol:

...unfortunately the mot would be a failure on emissions alone,

and there's no legal way around that one.

We have had cars in where the exhaust has been replaced in "quick-fit" type places and the cats thrown out, the garage having fitted an earlier system without realising, the emissions read +1.5%,0%, +1.5% CO as the lambda (oxygen) sensor works.....some performance systems do away with the cat and need "jumper" wires to by-passs the sensor, but they still need a cat for mot.
Of course, if its not used on the road....throw it away!

Am not an MOT tester but from poking around on tinternet it looks like a cat is not an MOT test requirement for diesels. It does however still have to pass the smoke/emissions test.

Decatting a car will only foul the ecu if there is a lambda sensor after the cat. To decat these systems the ecu will have to be remapped. On systems where there is only a lambda sensor before the cat, decatting is an option and will give UP TO a 20bhp or so increase BUT will more then likely fail the MOT as stated above due to emissions as the cat in most modern cars is essential for keeping emissions low. Best bet is to go for a stainless steel cat with a stainless steel monolith hi-flow (performance) cat. These will last for years providing your engine is kept in good nick. and give you UP TO 10 to 12bhp extra (depending on the car. These are available for fronteras but cost about £250.

Bugger, just wrote a long reply and bloody lost it!

Basic points were that if it is a problem ive got with the cat, then i would think to de-cat it, but keep hold of the existing cat for MOT time (for those that would worry about it, of course it would only be used offroad in the meantime!) It passed its MOT a month or so ago with that cat AND with the problem. I think its the contents of the cat shifting around so sometimes its clear and does its job, then other times it rocks into the wrong position and blocks the flow.

My Diagnostic tool is reporting an oxygen sensor problem so the mention of lambda sensors does make me think that there is some problem exhaust wise. Perhaps i'll change the sensor and see.

Anyway, thats not my BIG problem because thats not bringing on the EML. The EML only comes on intermittently on a run when i get loss of power, and as my diagnostic tool doesnt recover old fault codes, ive got to go out on a drive with the lap top and scan it as soon as the light comes on.... fun!!!

buy a 2.8 and de cat it . i done it a long time ago with no probs . also no lambda sensors or ecu on a 2.8 .
so no worries my. swb 2.8 is getting motd this week and i fully expect it to pass.

hi all, first post n all that :lol:

Used to work in a custom stainless exhaust company and I can tell you that as stated, a PETROL car registered after 1st aug 1992 DOES have to have a cat fitted, however a DIESEL does NOT need one fitted to pass an mot. it isnt even a cat on a diesel it is a particulate filter which over time, like all filters do, they get clogged up and will one day block up your exhaust and leave you stranded! (sods law dictates as far away from home as possible :twisted:

)

Yesterday i had the cat took out of my 2.8tdi and straight away noticed that the turbo spooled up a lot quicker (boost guage fitted) and revved a lot more freely uptop end, with absolutely no more visible smoke from the exhaust than with the cat left in place.

if you have a diesel with a cat in, get it cut out, your truck will do more to the gallon and go better to boot! and if you have a petrol, why not consider getting a de-cat pipe made up (or DIY) so you can slip the cat back in for tests? having the cat out will probably make it a tiny little bit louder but not much.

hope this helps somebody

cheers, Neil.

i got mine done by the professionals (bodie was good ) no more noise than usual
i recommend it . :wink:

Is it ok to cut the box out of the system and replace with a length of flexi pipe?

Dont see why not, so long as it goes back on again come MOT time, especially if its a petrol.

2.8 so no probs with mot (I hope).

DERV's don't require a Cat come MOT Time. So long as they pass the soot test then it'll pass.

Cheers.

Matt

after my little venture into home diagnostics, its emerged that the cat seems ok. I replaced the lambda sensor and everything is a lot smoother with no EML

Glad the thread brought out a few opinions though

yes from experience as long as your emmisions are ok :wink:

it cannot fail the mot

but you can be prosicuted by our friends in blue under the design and manufacture regulations (highly unlickly they would know it though) :wink: