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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > do all downpipes smell, throw CELs and fail emissions testing?



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      04-10-2015, 12:49 AM   #1
MountainStone
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do all downpipes smell, throw CELs and fail emissions testing?

Like the title says, are there any downpipes that don't smell, don't throw CELs and will pass an emissions test?

Thanks!
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      04-10-2015, 01:50 AM   #2
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Quote:
Originally Posted by MountainStone View Post
Like the title says, are there any downpipes that don't smell, don't throw CELs and will pass an emissions test?

Thanks!
Stock down pipe. Joke! Have you try hi flo cats?will still throw code though.
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      04-10-2015, 10:39 AM   #3
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You could go catted aftermarket DPs, however there's been reports of them going right back to their smelly ways quickly. Hi-flow cats have a lower cell count, and tend to drop in efficiency rather quick.

Go catless DPs, leave in secondary cats down stream, and install a DPFix when the time comes for inspection. If they use a sniffer, leave stockers in.
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      04-10-2015, 12:03 PM   #4
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In short, yes. All catless downpipes remove a major part of your emissions system, the catalytic converters.

By no accident there will be the smell of raw fuel / unburnt hydrocarbons.

The CEL can be avoided with either a tune like JB4 and Cobb or with a DP Fix. Although if you plan on getting catless downpipes you may as well get a tune. The tune adds a good 50-60WHP where as the downpieps alone won't add much power. With a tune the downpipes will add another 20-30WHP.
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      04-10-2015, 02:10 PM   #5
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Quote:
Originally Posted by MountainStone View Post
Like the title says, are there any downpipes that don't smell, don't throw CELs and will pass an emissions test?

Thanks!
Short answer yes
Long answer not really.
Catless DP do smell, but as long as the car is not sitting in idle for couple minutes you will hardly ever smell it. JB4 or Cobb will autoclear the tune so you wont have to worry about it. Can't give you any advice on how to pass emission testing.
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      04-10-2015, 03:27 PM   #6
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also depends if you have secondary cats in the exhaust. With secondary cats in place there is not much smell, if any.

Mike
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      04-10-2015, 10:33 PM   #7
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Thanks for all the responses. I have a JB4 so the CEL is the least-worrisome issue. I'll leave the secondary cats in place so I'm glad to hear the smell will be less of an issue (though I'd be interested to hear why my sophisticated modern automobile smells like unburned hydrocarbons when my old chevy small blocks never did). My concern becomes passing an emissions test. My town doesn't perform the sniffer on passenger cars and I passed my last test by just turning off the JB4. Will it pass if the JB4 is on and actively deleting the CEL? Do I have to reinstall the stock pipes every year to pass emissions or is there a third option?

Thanks everybody!
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      04-11-2015, 07:39 AM   #8
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Find out the laws on OBD2 readiness. If you can pass with the catalyst system "not ready" then you'll be fine. Otherwise you'll need a dpfix. In my area I'm allowed 1 not ready and it doesnt matter which one it is, so I'm able to pass with aftermarket cats.

BTW, I've had both catless and now have cobb catted downpipes. The catless do still smell but not nearly as bad. The cats also dampen the wastegate rattle noise a lot more.
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      05-03-2015, 09:43 AM   #9
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Quote:
Originally Posted by Mike@N54Tuning.com View Post
also depends if you have secondary cats in the exhaust. With secondary cats in place there is not much smell, if any.

Mike
Does a 2011 e90 335i with OEM PE have secondary cats?
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      05-03-2015, 01:16 PM   #10
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Mine doesn't smell too mad unless I keep it running inside a garage then my eyes will start to burn
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      05-03-2015, 01:44 PM   #11
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What's emissions? Lol. Don't have any in Florida. No inspections either as a side note.
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      Yesterday, 03:34 AM   #12
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Depends on the state. AZ allows one "not ready" for the obd2 scan and it doesn't matter which it is, so with my cobb set to auto clear cat codes I was able to pass just fine.
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