RESOLVED - De-Cat MOT problems (It passed). - Mercedes Benz SLK Forum

Performance MODS for the R170 Tuning and Performance modifications for your SLK

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#1 Old 03-27-2018
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RESOLVED - De-Cat MOT problems (It passed).

I am in the process of getting a Powerflow exhaust system in the UK.

The new exhaust system is going to go from the 2 inner catalytic converters near the manifold, removing the additional 2 cats further down the exhaust. So I will be left with 2 cats instead of 4.

Has anyone done this and if so, were the MOT fail issues going forward?
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#2 Old 03-27-2018
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I believe the biggest problem you will face is not one of emissions, but whether the tester will allow a pass when two of the four standard cats are not physically present. I am no expert but I think the 'normal' MoT requires all standard cats to be fitted and working.
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#3 Old 03-27-2018
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De-catted ( 2nd cats ) on my SLK 55 AMG and it made zero difference to the emissions.

The MOT operator wouldn't have known how many cats were fitted to a particular car anyway!

Reinstated the system before selling and the new buyer has just put some straight throughs on the car. Sounds brutal!
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#4 Old 03-27-2018
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Keeping the primary cats you should have no problem passing the emissions test! The secondary cats don't do a lot of work. They are there to catch anything the primaries miss whilst they are still coming up to temperature. Plenty of guys on here from the UK have done this on the 55 AMG model without issue. Some even claim to have passed an emissions test on just secondary cats after removing the primaries when fitting long tube headers. MOT testing will always be done with pre-warmed cats. Most MOT testers are ignorant to how many cats cars are supposed to have. I can't see you having an issue unless there's something in the new rules coming out this year?
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#5 Old 03-27-2018
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As has been said, no problem with those of us that have had the secondaries removed (and x-pipe to replace the centre resonator). Not exactly what you have planned, but check out the emissions link in my signature for some before and after numbers...


However, if you're planning a complete de-cat at some point, then that may be an entirely different story.
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#6 Old 03-27-2018
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I'm not trying to start an argument or be Mr. Clever-dick, but just to back up my previous statement have a look at the MoT test manual from the .gov.uk site, section 7.1.3
https://www.mot-testing.service.gov....4s07000101.htm

Whether or not any tester would know how many cats should be in place, the regs allow for failure if they are missing. That was my sole point.
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#7 Old 03-27-2018
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Quote:
Originally Posted by StirCrazy View Post
I'm not trying to start an argument or be Mr. Clever-dick, but just to back up my previous statement have a look at the MoT test manual from the .gov.uk site, section 7.1.3
https://www.mot-testing.service.gov....4s07000101.htm

Whether or not any tester would know how many cats should be in place, the regs allow for failure if they are missing. That was my sole point.
I imagine that, should an inspector's suspicions be roused by obvious changes/adaptions to an exhaust system, they MAY look into things further.

Certainly the new regulations and guidance for testers will be far more strict with regard to removal of DPFs from diesel vehicles.

Would be worth speaking to your local authority MOT station to see what their position is.


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#8 Old 03-27-2018
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Fit dummy or gutted 2nd cats
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#9 Old 03-27-2018
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Quote:
Originally Posted by dbgrn View Post
As has been said, no problem with those of us that have had the secondaries removed (and x-pipe to replace the centre resonator). Not exactly what you have planned, but check out the emissions link in my signature for some before and after numbers...


However, if you're planning a complete de-cat at some point, then that may be an entirely different story.
Quote:
Originally Posted by StirCrazy View Post
I'm not trying to start an argument or be Mr. Clever-dick, but just to back up my previous statement have a look at the MoT test manual from the .gov.uk site, section 7.1.3
https://www.mot-testing.service.gov....4s07000101.htm

Whether or not any tester would know how many cats should be in place, the regs allow for failure if they are missing. That was my sole point.
Mot testing has little profit unless fail work is done at the garage.
Most fails that come up seem to be the quick to fix unless rust/structure is involved.

If dummy boxes fitted, they'd likely get through if emissions test is ok.

But, as stated, if they spot it they can fail.
However, if you have bolt on dummies, you can be quickly road legal on a retest.

Unless they have/will add a rule about complete systems and not bolts.

Often discussed at meets.
I don't recall anyone getting failed. So if there are fails they are few.
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#10 Old 08-10-2018
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Thanks for all of the input guys. The car passed no problems!
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#11 Old 08-10-2018
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Originally Posted by muzTV View Post
Thanks for all of the input guys. The car passed no problems!

Great news!

As yet I have not come across a fail posted since the changes.

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#12 Old 08-10-2018
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Great news!

As yet I have not come across a fail posted since the changes.
Yup, kind of underlines the fact that some emissions equipment fitted by manufacturers was unnecessary in the first place.
Who has been conning who?
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Originally Posted by Windinmyhair View Post
Yup, kind of underlines the fact that some emissions equipment fitted by manufacturers was unnecessary in the first place.
Who has been conning who?
I suspect they looked at Ca, USA (and others).

Build one car for as many markets as possible.

Buyer will pay.
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