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      01-30-2016, 05:02 PM   #1
smithf80
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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.
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Last edited by smithf80; 03-12-2016 at 10:33 AM.
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      01-30-2016, 05:28 PM   #2
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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
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      02-01-2016, 10:29 PM   #3
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. . . .


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My Build Thread can be found HERE
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      02-02-2016, 12:25 AM   #4
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FINALLY......... Thanks smith!
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      02-02-2016, 01:49 PM   #5
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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?
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      02-02-2016, 02:23 PM   #6
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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.
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      02-02-2016, 02:24 PM   #7
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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..?
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      02-02-2016, 08:13 PM   #8
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Quote:
Originally Posted by Blubaron79 View Post
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.
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      02-03-2016, 12:09 AM   #9
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Quote:
Originally Posted by yoandry
Quote:
Originally Posted by Blubaron79 View Post
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
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      02-20-2016, 12:35 PM   #10
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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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      02-20-2016, 06:39 PM   #11
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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.
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      02-23-2016, 05:50 PM   #12
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Quote:
Originally Posted by smithf32 View Post
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 View Post
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
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      02-26-2016, 08:01 PM   #13
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Great post as this is a pretty common question.
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      03-06-2016, 09:55 PM   #14
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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, 12:20 PM   #15
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I unplugged the actuator. It's now open all the time.


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      03-10-2016, 05:05 PM   #16
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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 View Post
I unplugged the actuator. It's now open all the time.


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      03-10-2016, 05:08 PM   #17
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Quote:
Originally Posted by Anton_RU View Post
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.
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      03-12-2016, 06:08 PM   #18
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Yes! They made this a sticky!!
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      03-12-2016, 06:09 PM   #19
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Quote:
Originally Posted by Blubaron79 View Post
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.
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      03-12-2016, 06:13 PM   #20
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Quote:
Originally Posted by smithf32 View Post
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.
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      03-12-2016, 06:18 PM   #21
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Quote:
Originally Posted by Blubaron79 View Post
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.
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      03-16-2016, 10:02 PM   #22
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You unplug it at the exhaust? Not in the trunk like the E9x cars?
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