TerryO

The sound symposer on my 991 TT emits a constant-frequency drone in the cabin under throttle pressure. It is neither the sound of the engine nor the sound of the exhaust (both of which are desirable); it is just an annoying drone.

Has anyone plugged the symposer port on their 991 Turbo, as many have reported successfully doing on their 991 C2 and C4?

Is their something different going on with the Turbo that suggests another type of fix is required?

Thanks.

Terry

rjn1

Open rear boot, remove the plastic panel and fans, then disconnect the symposer pipe where it attaches to the rear bulkhead and where it attaches to the manifold pipe. Its attachments are squeezy oval shaped rings, which if you squeeze become circular and let you remove the pipe. Takes 60 seconds and no detriment other than getting rid of the whine.

LexVan

This has been done on the 991 Forum. Search there, too.

TerryO

rjn1, thank you for the "tubal ligation" directions. Most appreciated. Now, shouldn't I also plug the opening going into the cabin (to keep out noise, moisture, ....)? [Most of the 991 non-turbo forum posting describe leaving the tube in place, and just plugging/capping the opening from the cabin side.]


LexVan, thanks for the suggestion - I have read all of the posts in the 991 forum, prior to my original post, here. I am trying find out if there is anthing that needs to be done differently for the Turbo. So it would be great if several 991Turbo owners could weigh-in on their success/issues.

Also, does anyone know if the tube removal/capping has any impact on the various engine vacuum pressure sensors?

Thanks, folks. Keep the suggestions coming.

Terry

rjn1

Definitely no vacum issues.

You could put some tape over the hole in the bulkhead wall. It won't get any moisture in given its location.

On the manifold side the pipe is after the sound diaphragm so no issues there with ingress etc.

TerryO

rjn1: Thanks for the further info.

Now, when the sound diaphragm "opens", is their any problem it being exposed? i.e. would it be better to try to find a way to NOT have the diaphragm opening at all? [Now I am getting into a lot bigger set of issues. What would Porsche say?]

Terry

rjn1

My OPC didn't even notice I had removed the pipe. That probably says more about them though.

Given the bulkhead end of the pipe is exposed to atmospheric pressure all the time, don't see any issue with the manifold end port being exposed all the time either. When the valve opens that's further upstream of the diaphragm so it should be no issue.

Carcam

rjn1- thanks for the advice on how to disable the fake sound but I can't find which tube to disconnect...
I removed the fans and there was so little space to see and lots of tubes and connectors
Which side is it on- left or right? Can you take a picture or 2 to help out my simple mind Thanks!

speed21

Has your car had the symposer software upgrade yet?

TerryO

Speed21:
I do not know if my 991 TT has had the sound symposer upgrade. I bought the car a few weeks ago as a CPO. (It is a 2014 model year; delivered to the original owner last June; with very few miles on it when I received it) I was told by the dealer that the CPO process included software updates.

Can you tell me more about the Sound symposer upgrade? When was it first implimented? (My TT was probalbly build in April, and may or may not have had the update from the factory.) What did the update do?

Thank your for your help.

Terry

speed21

It entailed fitting longer pipes and changing the software. Apparently the original pipes from the engine to the symposer were a bit too short and some had reportedly popped off on certain cars causing vacuum leaks. Not sure if that affected the sound if they came off though (as it didn't happen to mine so I was told) but the S/Ware change did alter certain sound characteristics. I found that the snap crackle and pop on the over run disappeared on the normal mode entirely and was slightly muted in the sports mode as well if not by a great deal. Not sure if all that will help with your current issue as I had changed my exhaust at that stage so cant make any direct comparison there. I do know what you are referring to with the stock exhaust having an annoying drone at cruising speeds though, but whether these changes will cure that I can't say as I no longer have the stock system on my car thankfully. The most noticeable upgrade and improvement was the recent S/W upgrade involving the ECU idle settings. Now that one has noticeably reduced the cold idle volume, which was rather course and loud, and has also improved certain sound characteristics in the rev ranges where you are experiencing the drone. These changes are subtle but nice enough to be noticeable.

TerryO

Thanks, Speed21, for the insight. Most helpful for me in going back to a Porsche service center.

Anyone else with 991 Turbo sound symposer experiences? (There are a lot of postings for non-turbo 991s with symposer issues and solutions, but very few 991 Turbo positings.)

Terry

rjn1

You can check if all campaigns have been done by entering your VIN here:
https://recall.porsche.com/prod/pag/...f/VIN?ReadForm

I'm guessing that unless your dealer is proficient (yet to meet one, but it must be possible), there are various campaigns still live. Note that these are not safety recalls, which the replacement bonnet latch is, but just campaigns so the dealer has no obligation to notify you.

Three pics attached. First being the whole pipe, second being the bulkhead end - you can see how its ovaled and needs to be rotated 45 degrees to release from the bulkhead.

Third is the manifold end. You can see how the connector is oval shaped, and squeezing on the serrated parts makes it circular thereby releasing it.

The modified post campaign part no.s are 991.110.282.03 for the bulkhead end, which is connected to 991.110.019.70, which connects to the manifold and has the flexible corrugations as part of the tube.

If you are at the rear of the car looking forward with trunk open, fans removed and air intake snorkel removed (30 seconds), the pipe is on the left of center line and is the only pipe heading upwards to connect to the firewall. It's black plastic, 3.5 cm in diameter. Release the manifold end first, so you can rotate the whole pipe laterally (ie not twisting), to release from the bulkhead.

Carcam

Perfect rjn! Thanks a lot for going through the trouble. I was looking for a little tube. Out to the garage now

speed21

Good info there rjn! I take you have removed this tube now? Can you give us all a description of the sound changes and volume levels inside the cabin with it removed?
Is the snap crackle and pop all still there or is it reduced in volume? If so by how much in percent? With the stock system is all the drone gone once you remove the tube ? Or is it reduced by a certain percent? TIA.