Flap on 2009 35i Z4 exhaust pipe

[louisodwyer]

Hi all,
I have a beautiful 2009 35i Z4, 7-speed gearbox, with 48,000 kms.
On one of the exhausts at the back of the the car there is a metal flap that can block the exhaust and is controlled by what seems to be a vacuum unit.
Can anyone tell me what this is for and why it is on only one exhaust? I thought it might have something to do with the gearbox sports mode?
Many thanks....
Here it is - https://youtu.be/J4OZc2o13io

 

[Anonymous]

The noise flap is there for a few reasons..

It helps in certain drive by noise related tests

It is shut initially on start up to help the catalytic converters get up to temperature to be effective

It is altered by the comfort/sport/sport+ settings and whether the top is up or down

 

[louisodwyer]

Cool, many thanks!

 

[mcbutler]

You might well find it is stuck shut, mine was. You can also mod it so its open all the time, makes the car sound a lot better.

 

[louisodwyer]

Thanks for that - I suppose I need to check that it's working. Pbondar reckons it is closed on startup, that would be a place to start, then check the different conditions Pbondar mentions and see how it is behaving.... I would wonder why it would make a difference if the top is up or down?

 

[Smartbear]

Thanks for that - I suppose I need to check that it's working. Pbondar reckons it is closed on startup, that would be a place to start, then check the different conditions Pbondar mentions and see how it is behaving.... I would wonder why it would make a difference if the top is up or down?

To maximise the sound experience for the driver
Rob

 

[SV8Predator]

It is altered by the comfort/sport/sport+ settings and whether the top is up or down

Can you explain that more? For example, it stays closed on "comfort" and stays open on "sport", or the opposite? And what's happening if the top is down?

 

[Smartbear]

It is altered by the comfort/sport/sport+ settings and whether the top is up or down

Can you explain that more? For example, it stays closed on "comfort" and stays open on "sport", or the opposite? And what's happening if the top is down?

It’s not permanently closed in comfort mode, it just opens more often in sport mode. I think the valve’s open more often with the roof raised, it depends on rpm & throttle position i believe :?
Rob

 

[Anonymous]

Rob is correct there is a ‘map’ of mode setting / rpm / throttle position / top position that determines when it opens ..

As others said / have done you can ensure it’s kept open all the time and/or some people have installed a manual on/off switch..

 

[john-e89]

I had no idea it operated on all those functions. Every days a school day.

 

[bob4333]

If you want to experiment search "Golf Tee Mod" on google, or take a look at this vid for the mod. https://www.youtube.com/watch?reload=9&v=NYfZ5ZOW1cg

Simple to do and reversible if you change your mind. It lets a little more of the soundtrack out at low revs by allowing the valve to always remain open.

 

[SV8Predator]

Rob is correct there is a ‘map’ of mode setting / rpm / throttle position / top position that determines when it opens ..

Thanks for replying. But I'm not really any further ahead.

As I said in my original question: "For example, it stays closed on "comfort" and stays open on "sport", or the opposite? And what's happening if the top is down?"

Does anyone know what is happening at specific settings? You say there is a "map"? Do we know what changes to the flap (open or closed) due to the different settings? For example, I'm very surprised that the valve is open "more" with the roof raised? I would have thought the opposite.

 

[Anonymous]

It’s a multi dimensional issue...hence the expression ‘map’

The valve opens at certain different percentage throttle settings, certain RPM settings etc etc..

I’m not aware of anyone that has decoded the map and/or re-coded it..

The valve opens with the top down as the extra fresh air / noise helps dilute what could be a drone inside with the roof up...

If it’s any consolation you don’t have the active sound design which is fitted to the 18i, 20i, 28i 4 pots that injects fake engine noise into the speakers..

 

[SV8Predator]

the valve’s open more often with the roof raised,

The valve opens with the top down

Which is it?

If it’s any consolation you don’t have the active sound design which is fitted to the 18i, 20i, 28i 4 pots that injects fake engine noise into the speakers..

How do you know if this gadget is fitted?

 

[R.E92]

There's quite a bit of logic to when the exhaust valve opens, not really a simple answer to the question.

It stays closed during a cold start to reduce the noise generated by the increased idle speed and reduced engine timing, this lasts 1 minute. It then opens and remains open until the vehicle gets over 10mph at which point it closes again. Above 10mph the flap then uses a 3D map to determine if the flap should be opened or not which depends on gear, engine RPM and accelerator pedal position. There's 2 different maps, one for when the roof is up and one for the roof down. The flap opens more often when the roof is down.

You can customise all this behaviour with an ECU map. You can even make it so the flap remains always open in sport mode and such. I prefer just to keep it open at all times so change the speed threshold from 10mph to 180mph. I think it's a neater solution than sticking a golf-tee in a vacuum pipe

 

[Anonymous]

the valve’s open more often with the roof raised,

The valve opens with the top down

Which is it?

If it’s any consolation you don’t have the active sound design which is fitted to the 18i, 20i, 28i 4 pots that injects fake engine noise into the speakers..

How do you know if this gadget is fitted?

The ASD was only fitted to N20 ie 4 cylinder versions 18i 20i 28i..

It sits on the left rear bulkhead as you view it from the boot next to the comms unit..35i/23i30i don't have it..

https://www.newtis.info/tisv2/a/en/e89-z4-sdrive20i-roa/ned/03-body/01-noise/speakers-interference-noise/audio-output-fault-patterns/stereo-speaker-system/GaRdAReW

refers


On the N20 the exhaust flap has similar logic but conversely remains opens for a about 15-25 seconds on start-up due to different type of cat emission system

https://www.newtis.info/tisv2/a/en/e89-z4-sdrive20i-roa/ned/10-types-of-fault/01-noise/engine-noise/repair-instructions-n20/1VnXwJi6bC

refers

Picture of ASD unit in N20 here.. its the silver cigarette sizedbox to the left of the commbox