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emohawk11
Newbie


Joined: 01 Aug 2018
Posts: 27



PostPosted: Thu Oct 31, 2019 7:21 pm    Post subject: off side exhaust silencer valve stuck closed Reply with quote

Looking for some advice. I'd asked the OPC to take a look at the exhaust system whilst it was in for its service. The exhaust sounds rougher / throatier / more noisey / out of balance recently when at low speeds or idling in an enclosed area.

OPC checked and found a valvle in the exhaust to be stuck closed. They have advised replacing the rear silencer (£1500). I'm not certain however this will solve the original issue I'd asked them to investigate. It's my limited understanding that with the valvle closed exhaust gasses are diverted to the muffler reducing noise, and it's only over 3k (with PSE) or 4k (without PSE) revs the valve opens to increase noise.

Can someone confirm / give me a steer please as after spending this type of money i'd like to know the exhaust sounds as it should at all speeds.
 
  
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TonyC911
Nürburgring


Joined: 06 Jun 2016
Posts: 391
Location: High Wycombe


PostPosted: Fri Nov 01, 2019 8:15 pm    Post subject: Reply with quote

This is fairly typical of OPC's, why try and repair something when you can just replace it for 5 x repair cost! I would recommend you speak to your local indie if you don't want to tackle it yourself.

I need to caveat my reply by saying that I assume the 991 PSE system works on broadly the same basis as the 997...

The exhaust valves / flaps in the silencers operate via a vacuum. With the ignition off, the exhaust flaps are in the open position = PSE on. With the car started and the vacuum circuit complete, the exhaust flaps are closed = PSE off. When switching PSE on manually via the switch, there is no minimum RPM required, it activates immediately.

It is not uncommon for the valve actuator to fail in some way and this would be my suspicion given your symptoms i.e. the exhaust flap is not closing and consequently sounds louder.

It could be one of 4 things (or a combination of), the actuator has failed, the actuator linkage is broken, the exhaust flap has ceased/broken or the vacuum has failed due to pipework issues. As you can imagine things get extremely hot and are exposed in this part of the engine, so it is not unusual for these things to fail after several years. Replacing the whole box really should be a last resort.

I did a write-up on my 997 issues, which you might find useful, if only for the photos! - http://911uk.com/viewtopic.php?t=132422

Alternatively, someone more knowledgeable will be along to tell me the 991 set-up is completely different! Grin
 
  
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TonyC911
Nürburgring


Joined: 06 Jun 2016
Posts: 391
Location: High Wycombe


PostPosted: Mon Nov 04, 2019 8:04 pm    Post subject: Reply with quote

After my last post, I got rather curious about the set-up of the sports exhaust on the 991.1. Not least because I am considering having one retro-fitted to my car.

A little research and I found these images on an eBay listing. It now makes more sense why your OPC wanted to sell you a complete rear silencer

In the first photo I have highlighted the vacuum actuators which operate the linkage arms (one on each pipe), which in turn open and close the exhaust valves.

In the second/third image you can clearly see the linkage arms with the exhaust fitted to the car. You have good access from under the car, without having to remove anything, much easier than the 997! You should easily be able to diagnose the reason for the failure based on my previous post.

Hope that helps!
 



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emohawk11
Newbie


Joined: 01 Aug 2018
Posts: 27



PostPosted: Tue Nov 05, 2019 8:21 am    Post subject: Reply with quote

Hi,

Yes your observation is correct, the OPC have always in my experience replaced rather than fix.

The exhaust pictures you have are not quite correct for my 991.1. There's no central linkage. Video of system is here:

https://www.youtube.com/watch?v=_1ydTlJl96s

I'll let you know the results once the car is back.

PS - note if the valve is stuck closed I'd expect the exhaust to be quieter as it diverts exhaust gas to the side muffler.
 
  
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Robertb
Dijon


Joined: 01 Sep 2003
Posts: 7222
Location: South Oxfordshire

2002 Porsche 996 Carrera 4S

PostPosted: Tue Nov 05, 2019 12:18 pm    Post subject: Reply with quote

I'd be surprised if they are RPM activated as you could easily game the drive-by noise regs by keeping the revs low (as Ferrari did with the 355/360!).

This thread shows a pic of the standard 991 silencer removed - I'm guessing this is what you have. You can see the exhaust actuators.
https://www.6speedonline.com/forums/991/326435-subtle-exhaust-note-change-991s-3-8l-non-pse.html

You should be able to access the actuators from under the car (engine off and cold, clearly!) and give them a push at the ball joint end. They should move against the spring-loading. If your car sounds odd, I'd guess that the actuator rod is broken, so the exhaust flap is not open or closed properly and is just rattling/buzzing.

The actuators are available as separate parts - a good garage should be able to remove the silencer and switch the faulty actuator if that is the problem. The actuator looks very similar to the Designtek one I bought from design911 for £50 the other day. An OE 997 one is £100, and it may well be the same part for the 991.
_________________
"911- the guilt-free supercar"

Current: 2003 C4S Coupe, seal/black

Ex: '02 C4S Coupe, '96 993 Targa, '88 Carrera Sport Coupe

Last edited by Robertb on Tue Nov 05, 2019 12:43 pm; edited 1 time in total
 
  
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TonyC911
Nürburgring


Joined: 06 Jun 2016
Posts: 391
Location: High Wycombe


PostPosted: Tue Nov 05, 2019 12:19 pm    Post subject: Reply with quote

Yep, correct. It would be quieter / normal if the flap was stuck closed, they have likely miss-communicated the fault.

From your original post I had assumed you had the PSE fitted, below would be your back box config.

Good luck, hope it's a quick fix!
 



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gilford
Monza


Joined: 28 Aug 2006
Posts: 247
Location: Anglesey

2014 Porsche 991 Carrera 4S

PostPosted: Tue Nov 05, 2019 1:16 pm    Post subject: Reply with quote

Do you have a standard exhaust or PSE?

I've just had a PSE fitted to my car at an OPC and have the old exhaust sat out in my factory waiting to list it for sale, you can buy it if standard is what you are looking for?

It's of a 15k mile 2014 C4s.
 
  
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Hamster75
Spa-Francorchamps


Joined: 07 Sep 2017
Posts: 337
Location: Chester


PostPosted: Tue Nov 05, 2019 8:13 pm    Post subject: Reply with quote

Thanks for posting this my PSE 991.1 is working good but will save this thread for future reference incase of a problem Thumb
_________________
991.1 C2S Red
997.2 C4 White
924 Blue
 
  
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TonyC911
Nürburgring


Joined: 06 Jun 2016
Posts: 391
Location: High Wycombe


PostPosted: Tue Nov 05, 2019 8:58 pm    Post subject: Reply with quote

gilford wrote:

I've just had a PSE fitted to my car at an OPC and have the old exhaust sat out in my factory waiting to list it for sale


Can I ask how you find the sound of the PSE over standard? Is the difference when driving very noticeable? Do you feel it was good value?

I was also planning to have PSE retro-fitted, but now I am pondering replacing the rear muffler with a Sharkwerks pipe (used), which I could get fitted for around £900. Obviously it will be louder all the time, but I'm not too bothered about that, plus it's not my daily driver Question
 
  
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gilford
Monza


Joined: 28 Aug 2006
Posts: 247
Location: Anglesey

2014 Porsche 991 Carrera 4S

PostPosted: Wed Nov 06, 2019 1:30 pm    Post subject: Reply with quote

TonyC911 wrote:
gilford wrote:

I've just had a PSE fitted to my car at an OPC and have the old exhaust sat out in my factory waiting to list it for sale


Can I ask how you find the sound of the PSE over standard? Is the difference when driving very noticeable? Do you feel it was good value?

I was also planning to have PSE retro-fitted, but now I am pondering replacing the rear muffler with a Sharkwerks pipe (used), which I could get fitted for around £900. Obviously it will be louder all the time, but I'm not too bothered about that, plus it's not my daily driver Question


I'll be brutally honest -

When I bought my car it ticked all the boxes bar the PSE, the I took it out on a test drive and with sort plus engaged I thought I'd be happy without the PSE and bought the car there and then as it was mint with 13k miles.

Move on 6 months and my warranty was up for renewal, this along with an MOT needed gave me some bargaining power with my OPC so asked what would be the best deal they could do me on the PSE.

After a bit of tooing of frowing I got them down to £1800 fitted so pulled the trigger and boy am I glad I did!

The sound of the standard exhaust is fine at high revs but this PSE is just immense! We had a C2s with PSE when the 991 was first released in 2012 and it sounded NOTHING like this one! I'm not sure whether it's a combination of a run in car (now sitting on 17k miles) and a new system but boy does it howl! I test drove a few C4s's with PSE when hunting for this car and none sounded like this, I can't quite put my finger on it but it just sounds better Question

Basically....... I love it!
 
  
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TonyC911
Nürburgring


Joined: 06 Jun 2016
Posts: 391
Location: High Wycombe


PostPosted: Wed Nov 06, 2019 5:24 pm    Post subject: Reply with quote

gilford wrote:
TonyC911 wrote:
gilford wrote:

I've just had a PSE fitted to my car at an OPC and have the old exhaust sat out in my factory waiting to list it for sale


Can I ask how you find the sound of the PSE over standard? Is the difference when driving very noticeable? Do you feel it was good value?

I can't quite put my finger on it but it just sounds better Question

Basically....... I love it!


Many thanks, that's really helpful Thumb
 
  
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