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E90/E91/E92/E93 (2006 - 2013)
The E9X is the 4th evolution of the BMW 3 series including a highly tuned twin turbo 335i variant pushing out 300hp and 300 ft. lbs. of torque. BMW continues to show that it sets the bar for true driving performance! -- View the E9X Wiki

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  #1  
Old 08-15-2014, 10:10 AM
xarmx xarmx is offline
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rattling sound from 335i exhaust

I have a rattling sound coming from my left exhaust. I heard it's a butterfly flap that's causing it. I went to an exhaust shop and they said they can tack weld it open so it doesn't rattle anymore. Is this the only solution? Is this bad for the car on the long run?

It sounds a bit like this
_a__a2_
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  #2  
Old 08-15-2014, 10:20 AM
xarmx xarmx is offline
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rattling sound from 335i left exhaust

M 07 335i exhaust rattles upon start up. Usually when it's cold.
It sounds something like this
I have heard that I can tack weld the butterfly flap and it would stop the rattling.
Is this unhealthy for the car, is there another way to fix it?
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  #3  
Old 08-15-2014, 10:40 AM
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thekurgan thekurgan is offline
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Sounds like the flap actuator has seen better days. It's not unhealthy, purely mechanical noise silencer, it serves no power purpose aside from exhaust sound < 2500 rpm or so.
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  #4  
Old 08-15-2014, 11:20 AM
xarmx xarmx is offline
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Okay, thank you. I think imma get this done today
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  #5  
Old 08-15-2014, 11:30 AM
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thekurgan thekurgan is offline
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Quote:
Originally Posted by xarmx View Post
Okay, thank you. I think imma get this done today
You don't actually have to weld it open, you can do the golf tee mod, or pull the actuator in the trunk compartment. Either trick will leave the flap open; the actuator pull might cause a code to pop up, however.
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Old 08-15-2014, 11:35 AM
xarmx xarmx is offline
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What is better to do? Golf tee mod?

Last edited by xarmx; 08-15-2014 at 11:40 AM.
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  #7  
Old 08-15-2014, 11:42 AM
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Originally Posted by xarmx View Post
What is better to do? Golf tee mod?
I think if you want to leave it open, without service or techs bugging you about it being disconnected, the golf tee mod, or you can zip tie the hose as well.

Is this a sedan or coupe? I ask as the sedan can drone with this open all the time while the coupe has a different exhaust setup.
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  #8  
Old 08-15-2014, 11:48 AM
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CALWATERBOY DUE CALWATERBOY DUE is offline
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Quote:
Originally Posted by thekurgan View Post
Sounds like the flap actuator has seen better days. It's not unhealthy, purely mechanical noise silencer, it serves no power purpose aside from exhaust sound < 2500 rpm or so.

Aha! Increses back pressure @ low rom,
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  #9  
Old 08-15-2014, 11:51 AM
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thekurgan thekurgan is offline
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Originally Posted by CALWATERBOY DUE View Post
Aha! Increses back pressure @ low rom,
It does no such thing, esp. on a f/i car.

Here is the official BMW explination:-

Thank you for your email to BMW Customer Information.

We can advise that the exhaust flaps adjust at differing engine speeds in order to make the most effective use of the exhaust silencer. When the vehicle is running at idle or at low RPM, the flap ensures that the exhaust gases use as much of the silencer's volume as possible, keeping exhaust noise down, e.g. when you're in slow traffic or driving in high gear.

Whereas when the vehicle is running at high RPM, the exhaust flow characteristics are adjusted by the flap to give the exhaust gases a more direct route through the silencer, thus using less of its volume. This also has the effect of allowing the engine to rev more freely as there is less restriction on the exhaust flow.

The primary reason for the flap is to make the most effective use of the exhaust silencer volume at differing engine speeds.

We trust this information is of some assistance to you but if we can help you further at any time, please do contact a member of the BMW Customer Information Team.

Yours sincerely

BMW Group UK

Elfriede McNeal

Product Information Advisor

Ellesfield Avenue

Bracknell

RG12 8TA
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Last edited by thekurgan; 08-15-2014 at 12:00 PM.
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  #10  
Old 08-15-2014, 11:55 AM
xarmx xarmx is offline
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It's a coupe
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  #11  
Old 08-15-2014, 11:59 AM
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thekurgan thekurgan is offline
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Coupe = better sound from leaving the flap open.
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  #12  
Old 08-15-2014, 12:12 PM
MuffinMan91 MuffinMan91 is online now
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exhaust flap is done. i just pick up my 335 today from getting the same thing fixed under warranty. they replaced the left exhaust.

I've heard that just doing the golf tee mod will fix the rattle as well. haven't done it myself but from what i understand all you need to do is unplug one wire located somewhere in the trunk
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Old 08-15-2014, 12:17 PM
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Verts4Ever Verts4Ever is offline
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Originally Posted by thekurgan View Post
It's not unhealthy, purely mechanical noise silencer, it serves no power purpose aside from exhaust sound < 2500 rpm or so.
+1

There are also a few public statements from BMW about this over the years, in older owner manuals and even the press release announcing the MY11 E92 and E93 -- e.g., http://www.topspeed.com/cars/bmw/201...e-ar83859.html ("The 335i Coupe and Convertible dual exhaust system runs at both sides of the vehicle. At low loads, a flap channels most gas through one side to reduce low-frequency exhaust 'rumble.'")

Quote:
Originally Posted by thekurgan View Post
Coupe = better sound from leaving the flap open.
I can't speak to the E92, but the N55 E93 has a very annoying drone with the golf tee mod.
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Old 08-15-2014, 12:21 PM
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Originally Posted by Verts4Ever View Post
+1

There are also a few public statements from BMW about this over the years, in older owner manuals and even the press release announcing the MY11 E92 and E93 -- e.g., http://www.topspeed.com/cars/bmw/201...e-ar83859.html ("The 335i Coupe and Convertible dual exhaust system runs at both sides of the vehicle. At low loads, a flap channels most gas through one side to reduce low-frequency exhaust 'rumble.'")



I can't speak to the E92, but the N55 E93 has a very annoying drone with the golf tee mod.
haha, I was just searching for E93 and this mod. I wasn't sure if the drone would be there. Agree on the above, if you were to create backpressure, you wouldn't do it AFTER the muffler
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Old 08-15-2014, 12:25 PM
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Zooks527 Zooks527 is offline
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Quote:
Originally Posted by MuffinMan91 View Post
I've heard that just doing the golf tee mod will fix the rattle as well. haven't done it myself but from what i understand all you need to do is unplug one wire located somewhere in the trunk
For the "golf tee mod", you pull the vacuum line off of the actuator under the car and stick a golf tee into the line to plug it.

Or, you can remove the inner panel on the left side of the trunk by the left brake light. Unplug the connector found at that spot. This will unpower the actuator, but will also set a hidden code (no dash light) that the service techs will see and occasionally ask you about,
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  #16  
Old 08-15-2014, 12:37 PM
xarmx xarmx is offline
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Thanks for all the info guys! Will be leaving it open. The rattling sound really bothers me! And I'd rather have a louder exhaust
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  #17  
Old 08-15-2014, 01:15 PM
roadkillrob roadkillrob is offline
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My N54 E93 sounds great with the golf tee mod, no drone, like someone else reported though, the N55 with the golf tee mod drones more, I did it in my N55 X5 and then undid it as it was annoying.
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  #18  
Old 08-15-2014, 03:39 PM
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CALWATERBOY DUE CALWATERBOY DUE is offline
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Quote:
Originally Posted by CALWATERBOY DUE View Post
Aha! Increses back pressure @ low rom,
Quote:
Originally Posted by thekurgan View Post
It does no such thing, esp. on a f/i car.

Here is the official BMW explination:-

Thank you for your email to BMW Customer Information.

We can advise that the exhaust flaps adjust at differing engine speeds in order to make the most effective use of the exhaust silencer. When the vehicle is running at idle or at low RPM, the flap ensures that the exhaust gases use as much of the silencer's volume as possible, keeping exhaust noise down, e.g. when you're in slow traffic or driving in high gear.

Whereas when the vehicle is running at high RPM, the exhaust flow characteristics are adjusted by the flap to give the exhaust gases a more direct route through the silencer, thus using less of its volume. This also has the effect of allowing the engine to rev more freely as there is less restriction on the exhaust flow.

The primary reason for the flap is to make the most effective use of the exhaust silencer volume at differing engine speeds.

We trust this information is of some assistance to you but if we can help you further at any time, please do contact a member of the BMW Customer Information Team.
.

Now look Big K, and not to put too fine a point on it, but ol' Elfreda said it!

less restriction on the exhaust flow [flap open] = lower back pressure

ergo....

more restriction on the exhaust flow [flap closed] = higher back pressure

By Gum, I done good!

.




I felt it when did my Golf Tee Mod. But there was the unavoidable loss of torque and some other mildly adverse effects....I undid the deed....then she ran sweet!


.

Last edited by CALWATERBOY DUE; 08-15-2014 at 03:47 PM.
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Old 08-15-2014, 03:55 PM
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thekurgan thekurgan is offline
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Quote:
Originally Posted by CALWATERBOY DUE View Post
.

Now look Big K, and not to put too fine a point on it, but ol' Elfreda said it!

less restriction on the exhaust flow [flap open] = lower back pressure

ergo....

more restriction on the exhaust flow [flap closed] = higher back pressure

By Gum, I done good!

.




I felt it when did my Golf Tee Mod. But there was the unavoidable loss of torque and some other mildly adverse effects....I undid the deed....then she ran sweet!


.
I dig the comic, where do you find these things?

High rpm, not the same as low rpm, there is no way, something after the muffler (a single unit, btw), helps with low end torque in a turbocharged vehicle, hell, there aren't many BMWs that need two exhaust outlets anyway.

This is nothing more than a noise/drone suppressor. Ever wonder why aftermarket exhausts don't have a flap?

If you felt a difference, then there really is something in the bay area water, which is why I avoid our corp office.
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Last edited by thekurgan; 08-15-2014 at 04:43 PM. Reason: bad speller, really bad speller
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  #20  
Old 08-18-2014, 09:04 AM
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Verts4Ever Verts4Ever is offline
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Originally Posted by thekurgan View Post
Ever wonder why aftermarket exhausts don't have a flap?
Including the non-Euro spec BMW PE. Pretty sure die Ingenieure would have put a flap on all the PE versions if it aided performance.

Last edited by Verts4Ever; 08-18-2014 at 01:00 PM.
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  #21  
Old 10-10-2014, 09:09 AM
cwadebrickhouse cwadebrickhouse is offline
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I unplugged the connector on my 335i coupe. No issues whatsoever and a pleasant sound.
However I am trouble locating the connector on our 335i convertible. Anyone have a suggestion? the panels are completely different, I did remove the one behind the tail light alas no plug.

Thank You
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  #22  
Old 10-10-2014, 09:22 AM
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Verts4Ever Verts4Ever is offline
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However I am trouble locating the connector on our 335i convertible. Anyone have a suggestion? the panels are completely different, I did remove the one behind the tail light alas no plug.
You can also use a tie wrap to crimp the vacuum tube for the flap actuator. Same result, and (if you're still under warranty) it won't throw a shadow code visible to a potentially butthead service advisor.
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  #23  
Old 10-10-2014, 09:23 AM
jiveturky1 jiveturky1 is offline
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Quote:
Originally Posted by CALWATERBOY DUE View Post
.



I felt it when did my Golf Tee Mod. But there was the unavoidable loss of torque and some other mildly adverse effects....I undid the deed....then she ran sweet!


.
Why does the golf tee mod cause a loss of torque? Perhaps I'm reading it wrong.

-T
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  #24  
Old 10-10-2014, 02:20 PM
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Verts4Ever Verts4Ever is offline
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Why does the golf tee mod cause a loss of torque?
Long-running debate around here... Cal insists the flap is necessary for turbo back-pressure at low RPMs, others of us argue that it's only for noise reduction.

Cal is wrong, of course.
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  #25  
Old 10-10-2014, 03:29 PM
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floydarogers floydarogers is offline
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Back pressure sometimes good...

On newer cars (F3x) the flap is monitored and the SES will go on if you do the golf tee mod. BMW wouldn't have gone to that much trouble unless there were some measurable affect on the emissions.

One thing that has been brought up on the diesel forums is what happens to the turbo controls when the DPF (Diesel Particulate Filter) is eliminated/cored (sits right after the turbos). At least one tuner has noticed (or experienced) turbo overspeed/destruction after DPF removal. That's because the lower back-pressure screws up the boost control that depends upon pressure sensors before/after the turbos. That tuner refuses to sell a DP in place of the DPF unless they buy a tune that takes that into consideration.

Obviously, elimination of the flap will have a lesser affect than the DPF removal, but I could construe some effect on the pressure sensors for the gas engines, too. Speculation on that is beyond my job description...

Last edited by floydarogers; 10-10-2014 at 03:30 PM.
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