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MOT emissions on a decat downpiped 35i

Specific discussion about the E89 2009 Z4 (sDrive35is, sDrive35i, sDrive30i, sDrive23i)
stijohnny
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MOT emissions on a decat downpiped 35i

Post by stijohnny » Mon Aug 07, 2017 4:23 pm

I had my 35i fitted with decat downpipes a couple of months back when it was remapped and today it had the MOT!
Slightly nervous when the phone rang, it was the test center to say that the car had passed with no advisories.
So here are last years emissions (fully catted) compared to this years (decat downpipes).

2016
Fast idle - CO 0.02(limit 0.2), HC 6(limit 200), Lambda 1.0(limit 1.05)
Natural idle - CO 0.01 (limit 0.3)

2017
Fast idle - CO 0.026, HC 39, Lambda 0.996
Natural idle - CO 0.155

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Ducklakeview
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MOT emissions on a decat downpiped 35i

Post by Ducklakeview » Mon Aug 07, 2017 5:22 pm

The decat downpipes are removing the secondary cats, so the primaries - along with their sensors still take care of the emissions to a suitable level.

Mike

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MOT emissions on a decat downpiped 35i

Post by stijohnny » Mon Aug 07, 2017 6:51 pm

Ducklakeview
Thanks for the explanation. I thought we should be ok by just removing the cats in the downpipes, just not 100% certain as I hadnt seen any stats on it.

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MOT emissions on a decat downpiped 35i

Post by Player 1 » Mon Aug 07, 2017 7:53 pm

Ducklakeview wrote: Mon Aug 07, 2017 5:22 pm The decat downpipes are removing the secondary cats, so the primaries - along with their sensors still take care of the emissions to a suitable level.

Mike
Not on a 35i they aren't as far as I'm aware, the downpipes are those fitted directly to the turbo's with the sensors on.
Decat downpipes will require a remap to cancel put the check engine light.

Perhaps some clarification from the OP is required as to which cats are deleted?
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Ducklakeview
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MOT emissions on a decat downpiped 35i

Post by Ducklakeview » Mon Aug 07, 2017 8:12 pm

35i has secondary cats in the downpipes, as well as primaries at the manifold/turbos;
2017-08-07_20-10-33.jpg
2017-08-07_20-10-33.jpg (108.8 KiB) Viewed 1638 times
2017-08-07_20-09-45.jpg
2017-08-07_20-09-45.jpg (83.34 KiB) Viewed 1638 times
If the secondary's are removed (bottom pic) then there will be no codes or errors flagged, and a massive decrease in back pressure if mine were anything to go by!

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MOT emissions on a decat downpiped 35i

Post by Player 1 » Mon Aug 07, 2017 8:43 pm

That's correct however with the N54 engines its the primary cats that are more often removed for the extra power gained by allowing the turbo's to breathe easier. My understanding are that these are the ones referred to as downpipes as below:

https://www.mlperformance.co.uk/product ... y-delivery
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MOT emissions on a decat downpiped 35i

Post by R.E92 » Mon Aug 07, 2017 10:39 pm

Player is correct. Downpipes are where the primary cats are located.

Good to see that you can pass an MOT without them. Which brand of cat-less downpipes did you go for?

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Ducklakeview
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MOT emissions on a decat downpiped 35i

Post by Ducklakeview » Mon Aug 07, 2017 11:12 pm

R.E92 wrote: Mon Aug 07, 2017 10:39 pm Player is correct. Downpipes are where the primary cats are located.

Good to see that you can pass an MOT without them. Which brand of cat-less downpipes did you go for?
Which is exactly what I posted :tumbleweed:

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MOT emissions on a decat downpiped 35i

Post by R.E92 » Tue Aug 08, 2017 8:09 am

Ducklakeview wrote: Mon Aug 07, 2017 5:22 pm The decat downpipes are removing the secondary cats, so the primaries - along with their sensors still take care of the emissions to a suitable level.

Mike
This is what you wrote ^

Note the reference to removing secondaries when op has removed primaries.

Even if swap primary for secondary in that sentence it's wrong. The secondary cats don't use any sensors to take care of emissions, only the primary cats have anything to do with sensors.

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MOT emissions on a decat downpiped 35i

Post by Ducklakeview » Tue Aug 08, 2017 9:37 am

R.E92 wrote: Tue Aug 08, 2017 8:09 am
Ducklakeview wrote: Mon Aug 07, 2017 5:22 pm The decat downpipes are removing the secondary cats, so the primaries - along with their sensors still take care of the emissions to a suitable level.

Mike
This is what you wrote ^

Note the reference to removing secondaries when op has removed primaries.

Even if swap primary for secondary in that sentence it's wrong. The secondary cats don't use any sensors to take care of emissions, only the primary cats have anything to do with sensors.
The OP has not yet confirmed WHICH cats he has had removed.

Mike

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MOT emissions on a decat downpiped 35i

Post by stijohnny » Tue Aug 08, 2017 10:34 am

R.E92 wrote: Mon Aug 07, 2017 10:39 pm Player is correct. Downpipes are where the primary cats are located.

Good to see that you can pass an MOT without them. Which brand of cat-less downpipes did you go for?

The downpipes I used are by VRSF and I bought them from https://www.mlperformance.co.uk
These are the only ones I could find in the UK and the garage told me they were really awkward to fit.

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MOT emissions on a decat downpiped 35i

Post by Ducklakeview » Tue Aug 08, 2017 10:44 am

stijohnny wrote: Tue Aug 08, 2017 10:34 am
R.E92 wrote: Mon Aug 07, 2017 10:39 pm Player is correct. Downpipes are where the primary cats are located.

Good to see that you can pass an MOT without them. Which brand of cat-less downpipes did you go for?

The downpipes I used are by VRSF and I bought them from https://www.mlperformance.co.uk
These are the only ones I could find in the UK and the garage told me they were really awkward to fit.
Thanks for the confirmation - The sensors will either have deactivated during the remap, of a bypass module fitted if there is no error. Your secondary cats are now doing all the work, which is why the emissions are higher than last year, but still acceptable. They will be working "dumb" just processing the exhaust like an old "open loop" system, ie no monitoring of the pre and post cat gas.

Mike

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MOT emissions on a decat downpiped 35i

Post by R.E92 » Tue Aug 08, 2017 11:01 am

Ducklakeview wrote: Tue Aug 08, 2017 9:37 am
R.E92 wrote: Tue Aug 08, 2017 8:09 am
Ducklakeview wrote: Mon Aug 07, 2017 5:22 pm The decat downpipes are removing the secondary cats, so the primaries - along with their sensors still take care of the emissions to a suitable level.

Mike
This is what you wrote ^

Note the reference to removing secondaries when op has removed primaries.

Even if swap primary for secondary in that sentence it's wrong. The secondary cats don't use any sensors to take care of emissions, only the primary cats have anything to do with sensors.
The OP has not yet confirmed WHICH cats he has had removed.

Mike
Just read the initial post.

"I had my 35i fitted with decat downpipes"

Secondary cats are way down-stream from the downpipes!!
Last edited by R.E92 on Tue Aug 08, 2017 11:06 am, edited 1 time in total.

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MOT emissions on a decat downpiped 35i

Post by R.E92 » Tue Aug 08, 2017 11:05 am

Ducklakeview wrote: Tue Aug 08, 2017 10:44 am
stijohnny wrote: Tue Aug 08, 2017 10:34 am
R.E92 wrote: Mon Aug 07, 2017 10:39 pm Player is correct. Downpipes are where the primary cats are located.

Good to see that you can pass an MOT without them. Which brand of cat-less downpipes did you go for?

The downpipes I used are by VRSF and I bought them from https://www.mlperformance.co.uk
These are the only ones I could find in the UK and the garage told me they were really awkward to fit.
Thanks for the confirmation - The sensors will either have deactivated during the remap, of a bypass module fitted if there is no error. Your secondary cats are now doing all the work, which is why the emissions are higher than last year, but still acceptable. They will be working "dumb" just processing the exhaust like an old "open loop" system, ie no monitoring of the pre and post cat gas.

Mike
There still is monitoring of the gasses for the closed loop fuelling. The remap just removed the error code associated with primary cat efficiency.

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MOT emissions on a decat downpiped 35i

Post by jleckenby » Mon Feb 26, 2018 6:49 pm

Impressed you passed, how did you get around the readiness check? I had to fit a BMS fix to get it to show as ready.

I still failed miserably on emissions though!
Z4 35is, 438bhp
Cobb Stage 2 (Aggressive), VRSF Catless Downpipes, BMS DCI, NGK Iridium Spark Plugs, Eibach Springs

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