MOT emission fail. Catalytic converter at fault?

[k.alle]

Hi,


So I took the car for MOT over here and failed with 0.9% CO (Limit 0.3%) and likewise 0.9% CO (Limit 0.5%) at 2500RPM.
HC was at 100 (Limit 200) Lambda 1.0.

I have recently fitted a MaxxECU and tuned both idle (ign ~8 deg) and fast idle area to be @ lambda 1 on E85.

To me this seems to indicate that the 3" 100 cell race cat is not "igniting", we got the engine so hot it almost boiled but still no luck.
I fitted it after a successful MOT emission test and since then it has failed (also on motronic, similar numbers as now).
Previous cat was a 3" sports cat unknown cell number but I'm guessing ~300 cells or above.
Reason for changing to the new one was for less restriction obviously.

If I need to change cat again I would like to do it before mapping, since introducing more back pressure after mapping seems like a bad idea.
I have mild power targets, ~380-400hp on RS2 billet turbo setup.

Is my logic sound regarding that it is the cat at fault?

What sort of cat should I go for to performance / emission wise?
Race, sports, 200 cell, 300 cell etc.

Thanks for any advice.

[Henkjan]

I have a race kat (200 iirc, not sure) under my S2; after some years it failed MOT emissions test (4 gas), had to replace it. looking at the test results, the degradation of the cat was clear, it slowly erformed worse every year until it was so bad it needed to be replaced.

[k.alle]

Thanks for the reply Henkjan.
So 200 cell race cat should suffice for me I guess?

[Henkjan]

it did for me. our MOT procedure looks similar to yours

[k.alle]

Sounds good, I've ordered one now.
Lets hope that 200 cell cures it.

[audiman]

depending on the quality of the race cat, they tend not to last very long.
My recommendation would be to have your exhaust modified, so that you can simply bolt in a cheap 200 cell race cat for emissions tests and then remove afterwards and keep in the garage. That way it will last for several years

[k.alle]

I've got a home made 3" stainless turbo-back system on with v-bands all the way, so your recommendation should not be hard to do.
I'll keep it in mind if this cat gets me through emission testing.

[k.alle]

Good news, passed MOT emission test with a new 200 cell race cat.

New values,
Idle CO: 0.2
2500 RPM CO: 0.3 (a close call on that one)
HC 30
Lambda 0,99

I expect the 2500 RPM to improve somewhat with proper mapping.
Same goes for the idle CO I guess when I can get the idle properly dialed in.

Obviously the 100 cell version was flowing a bit too good or were too far from the turbo for proper heating.

[Wrath]

Kalle, what brand of the catalytic converter did you buy?
i think mine is scrap. And do you run around 8 degree ign on both idle and 2500 rpm? I have to run lambda 1.03 to clear hc and after a cylinder head rebuild it became better but not good. So I think my race cat that’s 6 years is to blame. Don’t know if it’s 200 or 300 cells

[k.alle]

Hi wrath,
I got a generic one from this place:
https://www.hova.com/race-katalysato...ell-universal/

I do 8 deg on idle, don't know if that is correct for E85 but it got me through at least.

Don't know for sure on 2500 but I would assume it is higher, I haven't messed with the supplied ignition map in areas above idle. I can check when I get home next week, I'm in Greece on holiday now.

If you know all else is all right then it should be the cat, no?

[Wrath]

Thank you

yeah it should be, Also have rebuild my head so i believe its the no name cat

[k.alle]

Wrath
Just checked the ign angle at 2500 rpm for you, seems to be 22-24 deg.