Butatista

Hi!

I am new to this forum but have lurked around for some time reading your opinions and advice as Porsche owners. I recently switched from a 718 GTS to a 2009 997.2 C2 MT6 with stock PSE (Aqua Blue Metallic...I love it).

However, I recently noticed a brief rattle at low revs from the exhaust but only with the PSE engaged. I had a PSC check it out and they concluded that it was the dampers in the active part of the PSE (vacuum controlled) that caused it. They only offered a replacement of the entire exhaust to a whopping cost of approx. 1700 Euros. So I took the car to an exhaust specialist workshop and they offered me to replace only the part with the damper and "vacuum box" for less than half the cost. They did the job and the rattle is now gone! Much joy!

However, driving home from the workshop I of course drow with the windows down to listen if the rattle was really gone and while doing so, I noticed a brief but clearly notable hissing sound (like a short burst of compressed air being released from somewhere in the system) every time I did an upshift. You know, almost like from a bus/truck when they shift gears (but of course not as loud).
It only happens when upshifting with PSE engaged. If I drive with windows closed I cannot hear it, but with windows down it is clearly noticeable.

I have not noticed this before and I wonder if this is normal but I just haven't noticed it before, or if there might be something wrong with the replacement part/repair job?

I write this post in hope of hearing your opinions/advice. Perhaps one of you with a similar setup can check if you experience something similar? Anyone had similar experience?

Thanks in advance!

Best regards
Martin

BLU997

The OEM PSE valves are spring loaded to be continuously open AKA "Normally Open", and only close when vacuum is applied. If you think the noise is related to the PSE, the only time there should be vacuum going to the PSE dampers is when the car is sending a "close" command to the PSE control solenoid.

I have a set of Ebay sourced, vacuum driven exhaust dampers in the shed, interestingly, they are "Normally closed" configuration, opposite of Porsche OEM PSE dampers. Did your tech install "normally closed" dampers opposite of OEM? To make NC dampers work, there has to be a change in the vac system hook up.

To eliminate the PSE dampers as a source of the hissing noise, you can disconnect the vacuum hoses going to the PSE activation solenoid. Be sure to block both hoses with golf tees (or similar) to ensure there is no vacuum loss nedded for other parts on the car.

Test drive car and listen for the noise. if the noise is gone, well, its gone, and the vac driven valves are the culprit.

Butatista

Hi!

Massive thanks for your answer, I really appreciate you taking time to help.

After reading your advice, I checked the data sheet for the newly installed vacuum driven exhaust damper (not OEM since Porsche only provides the entire exhaust as a spare part) and it says "open in neutral position". Based on your answer regarding how the OEM vacuum driven exhaust damper works, that should match without the need to change the vac system hock up, or do I missunderstand?

As I don´t have knowledge about how the vacuum system in the car works, I don´t know what could cause this hissing sound when upshifting. What air related system in the car has a correlation to the clutch/gearbox?

I´ll take a look and see if I can follow your advice to disconnect the vac hose from the PSE solenoid, but honestly I don´t know where they are located. Are they accessible from the engine bay or do I have to lift up the car to reach them from underneith?

Anyhow, it would be of value to me to hear if someone else experience the same hissing sound when upshifting with PSE active...it could be normal just that I haven´t noticed it before...

Thanks.

Best regards
Martin

Petza914

In sport mode, the valves still close at low RPM to boost low rpm torque, so there is vacuum being applied through the solenoid to the valves even when you have Sport mode on the PSE engaged. When you accelerate, vacuum is being removed so the valves go back to the open or sport mode and for some reason you're hearing that or you have leak in one of the lines running to the muffler valves. As mentioned, you can confirm this is related to the PSE system by disconnecting the electrical plug at the PSE vacuum solenoid and seeing if you still hear it. If not you need to test the vacuum line connections.

Butatista

Hi!

Thanks for your input. That sounds like a reasonable explanation to why I hear the hissing sound during upshift with PSE engaged. I don't have sport mode on my C2 (its pretty much a plain vanilla base 997.2 Carrera with the PSE as the only added option), does your theory still applies?

Based on the answers that I have received in this thread, I've spoken to a PSC about it and they suspect that the workshop might have missed to reconnect one of the vacuum hoses correctly when they reassembled the system. That theory is in line with yours so I suspect that is the case. I've spoken to the workshop and they will take a look at it on monday (it's midsummer weekend here now and everything is closed).

Best regards
Martin

Petza914

Yes, I'm talking about sport mode on the exhaust when pushing the button opens the valves.

Butatista

Thanks!

Butatista

Hi,

Since I first started this thread, the situation has become worse. I took the car to the workshop who had installed the new vacuum controlled exhaust dampers and had them check the installation and the hoses. They found nothing wrong but said that the sound was not caused by release of compressed air, they thought it actually was a high pitch rattling sound. Their theory was that it was the original Porsche vacuum damped on the other side that was causing the sound. So, I let them change that one as well...more money out of the pocket.

Driving home from the workshop some day later, the sound was still there. I took the car to a Porsche Service Center and let them have a look at it. They concluded that the sound came from the new vacuum dampers and that it was caused by some play in their assembly. So I took the car to the company that sells the dampers in my country (Sweden) and was treated very well. They offered to take a look at it and try to solve the issue. However, they could not find the cause to the sound, they found nothing unusual that could explain the sound. They test drove the car several times and could of course also hear the sound loud and clear, they had never heard anything similar before (and they are specialists at exhaust systems).

So here I am, now facing the whopping cost of approx 4 000 Euro letting a PSC change both sides to original Porsche exhaust (they only change the entire exhaust, not just the vacuum controlled dampers) or to live with the annoying sound. As you understand, nobody wants their 911 to sound like a bus shifting gears.

Tonight I filmed one of the new dampers at stand still in my garage, from startup (the damper closes as soon as vacuum is built up after startup) and then switching the PSE on and off. It is clear from the video that the return to open (no vacuum position) is not smooth, here is a link to the video:
The noise happens when rpm is falling below 2 200 rpm (even when shifting and the rpm falls below 2 200 for a short while before the next gear is engaged) and is very brief. Speed doesn't matter, the noise happens at first gear below 30 km/h and at higher speeds in all gears. There is also a rattling noise when driving very slowly (maneuvering a car park looking for a free spot) at low rpm.

Does anyone know the logic of how the PSE works when it is active? Is it in some way controlled by speed, rpm, gear...? The Porsche technician explained to me that the valves only are open below approx 2 500 rpm and that is why the noise happens when falling below that rpm, every singel time. To me, it sounds like the vacuum controlled dampers gets some serious work out if they open and close every time you fall below 2 500 rpm (change gear or just let the rpm fall below 2 500 with a gear engaged), is that really so?

As you understand, I am grateful and desparate for any advice that can help me in this bad situation that I am in.

Thank you

Best regards
Martin

Petza914

Here's a simple test to do. Disconnect the electrical plug from the vacuum solenoid in the enginencompartment. This will stop all vacuum from going through the lines to the exhaust valves. See if the noise is still there. If it is, then it's not related to the exhaust. If the noise is gone, then it is related to the exhaust.


Yes, even in sport mode, the PSE will close the exhaust valves at lower rpms. It does this to increase low end torque and then openz them at higher rpms to increase flow and HP, so if the valves aren't closing and holding vacuum, yiu could be hearing that air escaping as the driving situation varies and if not holding vacuum or requiring more vacuum than normal, yours are probably doing it more often than most.

Butatista

Thanks for the advice. I just tested to disconnect the electrical plug from the vacuum solenoid in the enginencompartment and and all rattle at low rmp and the strange sound when falling below 2 200 rpm is totally gone. I also filmed the damper on the right hand side at stand still afterwards and it doesn´t move when the PSE-button is pushed.

I´m not sure I understand how my car could open/close the dampers automatically more often than most, isn´t that controlled by some kind of computer controlled logic and should be exactly the same on all cars of this model? Hmm...if my car open/closes the dampers more often than others, that could explain why the original damper had to be replaced after just 65 000 km, it must be some extraordinary wear and tear if the vacuum controlled damper opens and closes with EVERY gearshift when the PSE-button is activated.

Best regards
Martin

Petza914

Now you know the cause of the issue. My point about yours doing it more than most related to a vacuum leak at that valve, which would be the cause of the noise. It takes a properly working valve very little vacuum to pull the springs in those valves. If yours has a vacuum leak or a stronger spring, the spring will override the vacuum earlier so your valves may open and close more easily with any change in vacuum from the solenoid. The commands from the system and controller would be kije every other PSE car, but the reaction from your exhaust different.

BLU997

Hi Martin,

have you simply tried to use wire and tie the actuator arms into the open position so they can't move?

In the open position, exhaust gas will pass freely past the valve butterfly and should not create any velocity related vibration from the butterfly sitting in closed position.

If the noise stops, you could have your answer.