Before you ask why your exhaust is broken and why only one side is dirty: READ THIS!

smithf80 · 01-30-2016, 03:02 PM

This question comes up all of the time, so I have asked a moderator, Dackelone, to sticky this so it can be at the top of the forum for everyone to see, although I'm sure this won't stop people from asking still.

It is completely normal for exhaust gas to come out of only one of your two exhaust tips, and for only one to look dirty most of the time.

This is because the exhaust on our cars is valved, meaning it has a "flap" inside one of the pipes, and can be controlled electronically by the car for various reasons. In most cases, the flap will be closed, and this is the default setting for both Eco Pro and Comfort mode, this is why you see one tip clean and one tip dirty. In Sport and Sport+, it is open.

Here is a summary of the function of the flap (to my best knowledge):

Flap closed on startup to help warm up the cat's faster.
Flap will open itself when the car reaches idle, and will typically open itself when the car is idling.
After driving away in either Comfort or Eco Pro, the flap will close, and remain closed unless you give the car hard throttle.
The flap will remain open in Sport and Sport+ mode.

If you car doesn't do what I described to the T, don't worry, it doesn't mean somethings wrong, the car's computer is very smart, and only under certain conditions will that flap open itself, so if you go out and start your car and it happens to be open, don't worry, maybe your cars already warm, etc, etc.

Hopefully this thread will help put to rest all of the questions about this function so we can all get back to complaining about other small, unimportant things.

Dackelone · 01-30-2016, 03:28 PM

Great write up.

Cross posting this thread...

F32 & F36 435i OEM Exhaust Valve Settings Different?
http://f30.bimmerpost.com/forums/sho....php?t=1156577

Only one exhaust steam?
http://f30.bimmerpost.com/forums/sho....php?t=1217585

ronanz · 02-01-2016, 08:29 PM

.

Project Elite · 02-01-2016, 10:25 PM

FINALLY......... Thanks smith!

otay · 02-02-2016, 11:49 AM

This is great. Maybe this sticky should be expanded / modified to include all FAQs for noobs?

- Exhaust on one side
- No temperature sync button
- Whirring noise when opening car door (fuel pump priming, i believe)
- What happens if I use regular gas

What else?

Blubaron79 · 02-02-2016, 12:23 PM

On my MPE both pipes open up after warm up even in comfort. Which my previous two 35i models did not with the stock exhaust.

Blubaron79 · 02-02-2016, 12:24 PM

Quote:

Originally Posted by otay

This is great. Maybe this sticky should be expanded / modified to include all FAQs for noobs?

- Exhaust on one side
- No temperature sync button
- Whirring noise when opening car door (fuel pump priming, i believe)
- What happens if I use regular gas

What else?

Why does my car beep at 37F..? Ha

Which is better: xdrive or rwd?

How can I change my halogen lights to HIDs or LEDs..?

yoandry · 02-02-2016, 06:13 PM

Quote:

Originally Posted by Blubaron79

On my MPE both pipes open up after warm up even in comfort. Which my previous two 35i models did not with the stock exhaust.

Yeap, same here.

Blubaron79 · 02-02-2016, 10:09 PM

Quote:

Originally Posted by yoandry

Quote:

Originally Posted by Blubaron79

On my MPE both pipes open up after warm up even in comfort. Which my previous two 35i models did not with the stock exhaust.

Yeap, same here.

Moral of the story is: buy the MPE

Brian_R · 02-20-2016, 10:35 AM

So the next question is, with all of this software controlled flap nonsense going on, why not have a binary flag flip on each startup to in essence "rotate" the exhaust path used for warm up on each ignition?

smithf80 · 02-20-2016, 04:39 PM

Quote:

Originally Posted by Brian_R

So the next question is, with all of this software controlled flap nonsense going on, why not have a binary flag flip on each startup to in essence "rotate" the exhaust path used for warm up on each ignition?

Because it's not that big of a deal and if you want to get technical, there's not much soot shooting out when it's at idle I don't think. Most of it comes when you're out driving and you step on it.

Bols · 02-23-2016, 03:50 PM

Quote:

Originally Posted by smithf32

Because it's not that big of a deal and if you want to get technical, there's not much soot shooting out when it's at idle I don't think. Most of it comes when you're out driving and you step on it.

Quote:

Originally Posted by Brian_R

So the next question is, with all of this software controlled flap nonsense going on, why not have a binary flag flip on each startup to in essence "rotate" the exhaust path used for warm up on each ignition?

That would also warrant the need of an extra flap in the second exhaust! Just not possible with the current installation. Don't think that would get past accounting either!

Nice of you to make this a sticky haha did see it being asked frequently!

In addition though one question: On the 28i (and possibly also the 35i) I've noticed that cold start RPMS vary sometimes. Sometimes it goes to about 1650 and it starts up LOUD. Other times it goes to about 1450 and it's much quieter.. Engine had the same amount of time to cool down, sometimes days.. Car probably has a reason for it but I can't seem to find a pattern

ASHpro · 02-26-2016, 06:01 PM

Great post as this is a pretty common question.

Rick Hunter · 03-06-2016, 07:55 PM

2016 F36 435xi here. Exhaust valve logic for other F3x does not equate to F36. Tried everything, and CANNOT get the valve to open. If there's another '16 F36 owner that has figured it out... don't bother explaining it to me... I've gone to option 2, and it took less time compared to everything I've done above.

Decided to do the U-Clip disconnect. 10 minutes total DIY, and no need to disconnect any harnesses. Easy to reconnect if I ever need to.

Here's a view of the clip in place from the other side of the exhaust:

Here's the clip (on my work towel :-)

...and the wire that keeps the flap in the open position:

hollandog · 03-07-2016, 10:20 AM

I unplugged the actuator. It's now open all the time.

Anton_RU · 03-10-2016, 03:05 PM

Hi, did you unplug it when the engine was running or no? I tried to unplug it with the engine off, and it let to the flap being always closed, even in the Sport mode.

Quote:

Originally Posted by hollandog

I unplugged the actuator. It's now open all the time.

hollandog · 03-10-2016, 03:08 PM

Quote:

Originally Posted by Anton_RU

Hi, did you unplug it when the engine was running or no? I tried to unplug it with the engine off, and it let to the flap being always closed, even in the Sport mode.

I did it when engine is off. I verified it with a flash light that it's open.

Blubaron79 · 03-12-2016, 04:08 PM

Yes! They made this a sticky!!

smithf80 · 03-12-2016, 04:09 PM

Quote:

Originally Posted by Blubaron79

Yes! They made this a sticky!!

Yeah, has been for a while, I PM'd a mod right after I made it. I was tired of seeing a new thread on this every... single... day.

Blubaron79 · 03-12-2016, 04:13 PM

Quote:

Originally Posted by smithf32

Yeah, has been for a while, I PM'd a mod right after I made it. I was tired of seeing a new thread on this every... single... day.

Yes..., but you know the thread will still pop up.

smithf80 · 03-12-2016, 04:18 PM

Quote:

Originally Posted by Blubaron79

Yes..., but you know the thread will still pop up.

Of course. Some people cannot be helped. I can only hope that it prevents a coupe of these threads from popping up.

SLOWER · 03-16-2016, 09:02 PM

You unplug it at the exhaust? Not in the trunk like the E9x cars?

01-30-2016, 03:02 PM	#1
smithf80 Major General 2916 Rep 5,366 Posts Drives: G80 M3 6MT Join Date: Mar 2014 Location: Long Island, NY iTrader: (1) Garage List 2022 G20 330i [9.00] 2018 F80 M3 [9.75]	Before you ask why your exhaust is broken and why only one side is dirty: READ THIS! This question comes up all of the time, so I have asked a moderator, Dackelone, to sticky this so it can be at the top of the forum for everyone to see, although I'm sure this won't stop people from asking still. It is completely normal for exhaust gas to come out of only one of your two exhaust tips, and for only one to look dirty most of the time. This is because the exhaust on our cars is valved, meaning it has a "flap" inside one of the pipes, and can be controlled electronically by the car for various reasons. In most cases, the flap will be closed, and this is the default setting for both Eco Pro and Comfort mode, this is why you see one tip clean and one tip dirty. In Sport and Sport+, it is open. Here is a summary of the function of the flap (to my best knowledge): Flap closed on startup to help warm up the cat's faster. Flap will open itself when the car reaches idle, and will typically open itself when the car is idling. After driving away in either Comfort or Eco Pro, the flap will close, and remain closed unless you give the car hard throttle. The flap will remain open in Sport and Sport+ mode. If you car doesn't do what I described to the T, don't worry, it doesn't mean somethings wrong, the car's computer is very smart, and only under certain conditions will that flap open itself, so if you go out and start your car and it happens to be open, don't worry, maybe your cars already warm, etc, etc. Hopefully this thread will help put to rest all of the questions about this function so we can all get back to complaining about other small, unimportant things. __________________ Scott, Partner Insight Automotive Consulting Click HERE for all discounted BMW New Car Pricing Click HERE for all BMW In Stock Inventory Specials Call/Text: 516-416-5481 Email: scott@insightautoconsulting.com Last edited by smithf80; 03-12-2016 at 08:33 AM..
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01-30-2016, 03:28 PM	#2
Dackelone European Editor 10772 Rep 22,992 Posts Drives: N54 e82 Join Date: Feb 2010 Location: Bayern, Germany iTrader: (1)	Great write up. Cross posting this thread... F32 & F36 435i OEM Exhaust Valve Settings Different? http://f30.bimmerpost.com/forums/sho....php?t=1156577 Only one exhaust steam? http://f30.bimmerpost.com/forums/sho....php?t=1217585 __________________ Dackel's European Delivery Museum Guide
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02-01-2016, 08:29 PM	#3
ronanz Gettin It Figured Out 1820 Rep 2,669 Posts Drives: 435i FBO PS2 bm3 w/ options Join Date: Jul 2014 Location: Southwest Region iTrader: (3)	. . . . . __________________ . My Build Thread can be found HERE
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02-01-2016, 10:25 PM	#4
Project Elite Captain 144 Rep 647 Posts Drives: F30 Join Date: Sep 2015 Location: Bay Area iTrader: (1)	FINALLY......... Thanks smith!
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02-02-2016, 11:49 AM	#5
otay Major 827 Rep 1,342 Posts Drives: 2015 335i Join Date: Aug 2014 Location: Raleigh, NC iTrader: (0)	This is great. Maybe this sticky should be expanded / modified to include all FAQs for noobs? - Exhaust on one side - No temperature sync button - Whirring noise when opening car door (fuel pump priming, i believe) - What happens if I use regular gas What else?
	Appreciate 2 Quote

02-02-2016, 12:23 PM	#6
Blubaron79 Brigadier General 1437 Rep 4,728 Posts Drives: 2021 M340i xDrive Join Date: May 2009 Location: PA iTrader: (0)	On my MPE both pipes open up after warm up even in comfort. Which my previous two 35i models did not with the stock exhaust. __________________ Current: 2021 M340i xDrive Previous: '18 340i xDrive; '15 335 xDrive; '14 435i xDrive; '09 335 E92 xDrive
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02-20-2016, 10:35 AM	#10
Brian_R Private 30 Rep 91 Posts Drives: 16 340, 08 H3 Alpha, 04 TSX Join Date: Dec 2011 Location: PA iTrader: (0)	So the next question is, with all of this software controlled flap nonsense going on, why not have a binary flag flip on each startup to in essence "rotate" the exhaust path used for warm up on each ignition?
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02-26-2016, 06:01 PM	#13
ASHpro The General***** 12 Rep 45 Posts Drives: M440xi GC Snapper Rocks Blue Join Date: May 2015 Location: GTA iTrader: (0)	Great post as this is a pretty common question.
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03-06-2016, 07:55 PM	#14
Rick Hunter Skull Squadron Leader 309 Rep 2,031 Posts Drives: '07 M Coupé & '16 435xi GCoupé Join Date: May 2007 Location: The Emerald City iTrader: (20)	2016 F36 435xi here. Exhaust valve logic for other F3x does not equate to F36. Tried everything, and CANNOT get the valve to open. If there's another '16 F36 owner that has figured it out... don't bother explaining it to me... I've gone to option 2, and it took less time compared to everything I've done above. Decided to do the U-Clip disconnect. 10 minutes total DIY, and no need to disconnect any harnesses. Easy to reconnect if I ever need to. Here's a view of the clip in place from the other side of the exhaust: Here's the clip (on my work towel :-) ...and the wire that keeps the flap in the open position: __________________
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03-07-2016, 10:20 AM	#15
hollandog Major 448 Rep 1,056 Posts Drives: F30 Join Date: Nov 2011 Location: nyc iTrader: (0) Garage List 2016 BMW 340i [9.00]	I unplugged the actuator. It's now open all the time. __________________ 2016 340i \| Estoril Blue \| Coral Red \| M Sport
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03-12-2016, 04:08 PM	#18
Blubaron79 Brigadier General 1437 Rep 4,728 Posts Drives: 2021 M340i xDrive Join Date: May 2009 Location: PA iTrader: (0)	Yes! They made this a sticky!! __________________ Current: 2021 M340i xDrive Previous: '18 340i xDrive; '15 335 xDrive; '14 435i xDrive; '09 335 E92 xDrive
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03-16-2016, 09:02 PM	#22
SLOWER Lieutenant Colonel 310 Rep 1,733 Posts Drives: 2003 M3 Join Date: Apr 2013 Location: MA iTrader: (8) Garage List 2024 BMW X5 M60i [0.00] 2003 M3 Convertible [0.00]	You unplug it at the exhaust? Not in the trunk like the E9x cars?
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