996 PSE exhaust going oddly quiet until 3500rpm

[radial]

To all 996 owners with PSE, especially those with a 4S. 

 

I think my 996 C4S exhaust behaves oddly. I think it's a fault but you might tell me it's normal behaviour. The problem is that I've always had this 'fault' on my car so I don't know if it's a fault or intentional behaviour. If you have the same car, perhaps you can shed some light on this.

 

When I start it, it's noisy and sounds great. It quiets down as it runs for the first 5 mins. 

 

I have the PSE system and when I press the button you can audibly hear the exhaust note change - quieter when on and louder when off. Default is off so loud.

 

Here's the rub. Up to around 1500rpm it's got a good noise then it fades out to the point where it's so quiet it's like driving my partners Yaris. If I keep accelerating, when I get to around 3500rpm the exhaust suddenly gets loud again. I mean it's immediate - like someones flipping a switched marked loud. It sounds great. 

It happens in 2nd and 3rd gears most noticeably and the PSE is in the 'off' position. If I have the PSE button on, then it's just quiet all the time and that works fine.

 

So why the silent spot?

I did read somewhere that German market cars might have had a system that turns on and off the PSE at certain speeds to prevent people driving round residential streets with a loud exhaust but information is thin and I don't think I was ever on UK cars. 

 

I have also had a small go at checking vacuum pressure at idle on both sides of the Y piece in the engine bay but both hold good pressure. One side has only a microscopic leak but not enough to cause this kind of issue. 

[JFP in PA]

22 minutes ago, radial said:

To all 996 owners with PSE, especially those with a 4S. 

 

I think my 996 C4S exhaust behaves oddly. I think it's a fault but you might tell me it's normal behaviour. The problem is that I've always had this 'fault' on my car so I don't know if it's a fault or intentional behaviour. If you have the same car, perhaps you can shed some light on this.

 

When I start it, it's noisy and sounds great. It quiets down as it runs for the first 5 mins. 

 

I have the PSE system and when I press the button you can audibly hear the exhaust note change - quieter when on and louder when off. Default is off so loud.

 

Here's the rub. Up to around 1500rpm it's got a good noise then it fades out to the point where it's so quiet it's like driving my partners Yaris. If I keep accelerating, when I get to around 3500rpm the exhaust suddenly gets loud again. I mean it's immediate - like someones flipping a switched marked loud. It sounds great. 

It happens in 2nd and 3rd gears most noticeably and the PSE is in the 'off' position. If I have the PSE button on, then it's just quiet all the time and that works fine.

 

So why the silent spot?

I did read somewhere that German market cars might have had a system that turns on and off the PSE at certain speeds to prevent people driving round residential streets with a loud exhaust but information is thin and I don't think I was ever on UK cars. 

 

I have also had a small go at checking vacuum pressure at idle on both sides of the Y piece in the engine bay but both hold good pressure. One side has only a microscopic leak but not enough to cause this kind of issue. 

 

Actually, it was the Swiss market that led to this.  Factory installed PSE will automatically go to the quiet mode between certain KPH vehicle speeds to spare the neighbors ears.  Normal behavior unless you defeat the control system.

[radial]

Super thanks @JFP in PA

Defeating the system is now my aim :)

Someone else suggested that I can disconnect the speed signal wire to the relay in the passenger footwell?

[JFP in PA]

1 minute ago, radial said:

Super thanks @JFP in PA

Defeating the system is now my aim 🙂

Someone else suggested that I can disconnect the speed signal wire to the relay in the passenger footwell?

 

The quickest, and probably easiest as well, method to disable the system entirely is to disconnect and plug the vacuum lines running to the vacuum chambers on each side of the PSE under the car.  Vacuum is used to close the valves, making the system quiet, unplugged, it will be forever in the loud mode.  Enjoy 🙂

[radial]

Now that sounds like a fun plan @JFP in PA :)

If I wanted to try by temporarily removing the speed sensor wire from the relay do you have any idea where I could find that? Someone told me I can disconnect that also but I'm not sure where it is other than the passenger footwell (or did they mean the right footwell, which on my car is the drivers?).

[Richard Hamilton]

The relay is on the panel in the driver side footwell (RHD).  It has abgasklappen written on the top of it.

 

Check this out. 

 

Edited June 16, 2020 by Richard Hamilton

[Michael Laity]

I added a switch to the top of my relay so if I ever wanted it to go back to normal. I've never touched the switch.

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