E89 Z4 20i Exhaust Flap

[E89Pilot]

Hi Folks,

What’s the normal operation of the exhaust flap for the 20i, in other words how do I know if it’s working or stuck open?

I can see mine is open when parked and stays open when I start the car. When can I expect to see it move?

TIA

[SV8Predator]

Hi there and welcome to the forum!

I asked the very same question when I first bought my 20i three years ago. I'm still none the wiser.

I've done the (in)famous "golf-tee" mod now, and it is a little bit noisier. Maybe there some new information for you.

[E89Pilot]

Hi,

Thanks My gut feeling is that the flap is stuck open on my car, I’ve never seen it closed. I have to investigate to see if it’s seized or if it’s been modified. It’s really hard to find any info on the normal operation - most threads I’ve found are how to modify flap so that it stays open! It sounds ok, but I’d like it to work as intended.

[Pondrew]

The flap should be open pretty much whenever you can see it. It is vacuum operated via a little tube from the engine (unless it's been unplugged AKA 'the golf tee mod').
The valve will be open when the engine/ exhaust cools down so it is ready for the next 'cold start'. On cold start the valve is open to get rid of the rich gases quickly. As the engine/ exhaust warms it will shut. During 'normal' driving it will stay shut (although you can't see it obviously) until you give the throttle some 'beans'. Then it will open to prevent back pressure build-up in the exhaust and to get rid of the increased gases quickly through both outlets.

I don't know what controls the vacuum pipe to the valve, but the above is a very basic idea of what is going on.

An easy way to check it is working is to start the car, let it idle for a few minutes, then you should see the valve shut.

[E89Pilot]

That’s great info! Thanks! I’ll let it idle a while and see what happens

[jamesgarbett]

"thread resurrection"

does anyone have a photo of the exhaust with the flap in the open and closed positions?
I assume it's in the right most pipe ?

[jamesgarbett]

ok now i've discovered that Bimmerlink enables you to open and close the flap i can see whats happening

basically my flap is always closed unless i help it open with a screwdriver (when Bimmerlink is set to "Open")
I can see the actuator mechanism moving but it looks like this isnt enough to open the flap unless i poke at it
i've tried some WD40 to see if that helps free it up

[Pondrew]

i've tried some WD40 to see if that helps free it up

That will burn off as soon as the exhaust gets warm TBH.
I would try some high temperature lubricant if it's a bit sticky.

You could have a leak in the vacuum hose somewhere, of course.

[jamesgarbett]

thanks - could be
i don't think it's jammed as it moves easily with a slight push from a screwdriver once set to Open
i think maybe the vacuum isnt providing the required force to open it - the flap "axle" is definitely moving though
anyway i just drove the car with the flap open all the time and can barely hear a difference so not going to bother now!