New 2019 S4 - Only one tail pipe being used at idle
 

Hey Guys

Firstly, I apologies i'm sure this question has been asked a lot and i have searched the web and this forum, but didn't see a definitive answer (found an answer for an S5, not S4).

I just changed from a 2016 S3 to a 2019 S4. On the S3, when using Auto or Comfort only the two inner pipes of the 4 were used. In Dynamic all 4 were used. I could tell based on the soot pattern on the exhaust.

This morning I noticed that of the 4 tail pipes on my new S4 only one, the 3rd from the left (looking from the back) was sooting up. When I parked the car I jumped out and noticed that only that one pipe had warm air coming out of it. I was expecting the tail pipes to behave in the same way as my S3 with the inner two running. So can someone confirm that on an S4, only the 3rd from the left is open at all times ? And in what circumstances do all 4 open ?

Thanks.

Yes, it's true. If you look under the car you can see the 2 valves that open and close to control the flow. If you use dynamic mode or set the engine noise to dynamic in individual mode, then all 4 will be open all the time.

This is the exhaust. The black things are valves and there is a wiring harness that plugs into them. As you can see from the valve locations it can operate with 1, 2, or 4 tips open.

Dynamic mode will cause them to be more open more of the time, comfort the opposite. You can hear the difference. I believe it says right in the manual that it isn't recommended to run the exhaust in comfort mode in performance driving e.g. track scenarios but boy does it help cut the drone out on road trips and every day commuting / making your neighbors not hate you.

It is also possible to unplug the valve controllers and the tips will remain 100% open 100% of the time, there are several threads on this subject with detail on how to do it as the connectors are reportedly a little tricky.

https://cimg0.ibsrv.net/gimg/www.aud...18c08e1f45.png

In Dynamic mode, should all 4 be open, even when in park idling ? Or does it close them until you start driving ?

Wow, thank you, that picture REALLY help !

I've wondered this question myself and I think the answer is no, I believe perhaps for the first ten seconds or so all 4 tips do open (the car is noticeably louder) while it runs its rich startup cycle, but then they partially close and the car quiets down considerably even in dynamic while parked / idling. The computer will open the tips as needed to deal with increased exhaust flow as power output increases under load/acceleration though. It's an intelligent system that takes several conditions into account and the primary one over which you have control, on the stock system at least, is the Drive Select mode (dynamic vs. comfort exhaust sound).

The valves are either opened, or closed. There is no in between. In dynamic mode all of the tips are open all of the time, even in park. You can just look under the car and see it for yourself. I know because I did that with my coworkers one day. Having all four tips open also increases the burble sound it makes when you let off the throttle, but this also slightly reduces your fuel economy.

In other modes the valves are opened or closed (fully) based on engine demand, and yes it does state in the manual to run the valves fully open on the track.

Do all four stay open in Individual mode with the transmission in D, but engine sound set to Dynamic? This is what I have been running for a while because I like the exhaust note and the more equal soot distribution is easier to clean and takes longer to become noticeable.

Yes I believe it does. Even when you are in park. Turn on the car, roll the windows down, then go into individual settings and toggle the exhaust sound. You can hear the valves clicking open and shut.

Correct me if I'm wrong, but I'm fairly certain I'm right here.

Wouldn't the fact that only one tail pipe being used at idle is because the exhaust air volume/heat cannot keep both cats in both pipes at the optimum temperature? I believe my vehicle operates the same way.