[rightrudder]

So, suppose on cold start I immediately select Sport+ mode. Does the exhaust flap open immediately, or is there a warm-up period before it opens?

[SlickShift]

From what I've experienced it still needs to warm up a little before it opens regardless of driving mode.

[rightrudder]

Originally Posted by SlickShift

From what I've experienced it still needs to warm up a little before it opens regardless of driving mode.

Ah, that's probably a good thing for neighbor relations, when I head out early!!

[TheCaptain]

On a cold start, the exhaust flap is OPEN from the beginning, regardless of the driving mode setting. That's why it's loud and burbly and not quiet when you start it up. They've been like this since the N54 engine or maybe even earlier. If you're in comfort mode, it will then close and run quietly after a short period. I've never timed it but it seems like it takes about 15 seconds. If you change it to sport+, the flap will just stay open.

[orangeglim]

Mine is definitely not OPEN when the car turns on. It's closed. I can look in the tail pipe and see this happening. It opens a few minutes later and exhaust comes out of both tail pipes.

[moldcad]

^ This

Piotr

[jmwilson125]

Originally Posted by TheCaptain

On a cold start, the exhaust flap is OPEN from the beginning, regardless of the driving mode setting. That's why it's loud and burbly and not quiet when you start it up. They've been like this since the N54 engine or maybe even earlier. If you're in comfort mode, it will then close and run quietly after a short period. I've never timed it but it seems like it takes about 15 seconds. If you change it to sport+, the flap will just stay open.

Coulda sworn this was correct.

[rightrudder]

A lot of carmakers have a cold-start regimen where the idle is higher, and extra fuel plus retarded timing stoke a nice little fire in the exhaust manifold to light off the catalyst as early as possible. Maybe the higher revs make it sound like it's open?

[Kidu]

I think thats what it is. I have a Dinan Exhaust which does NOT Have a flap and yet cold starts are loud!

[TheCaptain]

Originally Posted by orangeglim

Mine is definitely not OPEN when the car turns on. It's closed. I can look in the tail pipe and see this happening. It opens a few minutes later and exhaust comes out of both tail pipes.

How can you see in the tailpipe when you start the engine? On my car it closes pretty quick, maybe yours is closing within the few seconds it takes to get out and walk to the back of the car.

[orangeglim]

It is closed. That's what I said. It closes immediately on starting the engine.

[TheCaptain]

On my car it's initially open at startup, and then it closes after a few seconds, and you can hear a faint metal "tink" sound when it slams shut if you listen carefully. I initially said it takes about 15 seconds, which is about the right timing for the flap on a 135, but I had a second person watch and it closes on my 235 after only a few seconds.

Also, I'm talking about a genuine cold start where the ambient air temperature is low and the engine hasn't been started since the previous day. The system uses a range of variables to determine the position of the flap, and it will behave differently depending on the conditions.

[Hellrot]

Mine is definitely open on "cold" starts and then closes.

I have the M exhaust, not sure if that matters.

[Maynard]

Originally Posted by TheCaptain

On my car it's initially open at startup, and then it closes after a few seconds, and you can hear a faint metal "tink" sound when it slams shut if you listen carefully. I initially said it takes about 15 seconds, which is about the right timing for the flap on a 135, but I had a second person watch and it closes on my 235 after only a few seconds. ....

This is reassuring - couple of coldest mornings last winter mine made a less encouraging sort of grinding clunk noise, and I was hoping it was these flaps moving about (after about 10 minutes of unsuccessfully trying to provoke the noise again with brakes or U-joints, so I was fairly confident it wasn't s/t real expensive).

[TigerTrump]

When I tested my car, it depended upon the mode the car was in when it was last turned off; so if it was in sport mode when turned off, which it normally is, then the flap starts off open then closes within a few seconds of the cold start, despite Sport mode being pressed as soon as the car is started. The flap then opened again after a few minutes. If the car was last turned off in comfort mode, the flap was already closed and stayed that way after a cold start up for a few minutes despite sport mode being pressed as soon as the car started. The flap then opened once warm.
The above does not happen anymore, I unplugged the exhaust valve when it was open.

[Isolde]

This all makes little sense. On cold starts it is loud but the exhaust only exits the right tip. Then after 15 seconds it suddenly mutes but is still only coming out of right tip - implies change in ignition timing and no valve change. Then once warm if in sport mode the valve opens to allow exhaust through both exits.....

[moldcad]

..., but is hardly louder!

I couldn't have described it better than you did, Isolde

Piotr

[TheCaptain]

Isolde, I'm curious about the point you made, can you elaborate on the ignition timing and how it relates to which side of the muffler the exhaust exits from?

[3.0L]

Originally Posted by TigerTrump

I unplugged the exhaust valve when it was open.

This sounds like the best solution.

Question: Did unplugging the exhaust valve actuator cause a CEL?

[Kolyan2k]

The flap is there to warm up the cats when car is cold. Closed means cats warm up quicker. Unplugging in e90 would throw a shadow code, no CEL, but dealer can still see the error

Secondary function might be to regulate the noise, but I am not sure and haven't tested it.