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dcboxster

PSE (Deeper Sound when Fans Cut in)

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Gents,

I had a PSE on a previous 996 (1999) and pursched a newer 996 (2003) recently with a PSE installed (without wiring) and have noticed the following:

Occasionally, when I am sitting in traffic, I will hear what I think is the cooling fans cutting in (after I've been stationary for a while) and if I then blip the throttle, the PSE's are momentarily much deeper in sound.

My PSE sounds great in normal use, but when the above occurs, is f**king awesome!

Anyway, I just wanted to check if this was normal and if anyone has a more technical explanation of why this happens.

Many thanks in anticipation of a response.

Regards,

Dave

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Maybe time to clean the front radiators.

PSE should not change it's tone if no wires are connected - because the mechanical valves are always open when there is no electronic control.

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The only thing that would change that I can think of is the RPM might drop slightly as the fans come on as the alternator load would be increased. No idea why it would change the exhaust note so much.

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I have a '04 996 with the factory PSE fitted - Not sure if this is related but I have noticed that when my engine & exhaust is cold the PSE is quite loud and agressive even at low RPMs (2 to 4K).

When driving around and allowing the engine and exhaust components to fully heat up, the exhaust note is definitely quite a bit different - At high RPM the PSE still sounds fine when the components are hot but it loses the low RPM tone/bark and the PSE sounds very quiet until the engine is wound up past 4K rpm.

Mine is controlled by the switch on the dash - I have been thinking lately that maybe somehow the muffler valves are possibly closing slightly on the mufflers as the whole exhaust becomes hot when driving for 30mins+ ??

I can sometimes also hear a tinny sounding rattle as I accelerate at low speed which I think is one of the vacuum operated valves rattling on the mufflers as I have heard of other cars with similar symptoms in the past - I may need to pop my head under the car and see if I can temporarily physically 'Lock' the muffler valves in the open position to verify this.

Edited by ZX7R

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The valves are closed with engine vacuum (your switch actuates an electrical solenoid). So check operation of the switch and the vacuum lines.

The valves are normally open (loud).

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I'll temporarily disconnect/seal the vacuum lines at the solenoid to see if this has any effect to try and isolate the issue.

I was thinking along the lines that the actual mechanical valve on the muffler(s) may be possibly moving somewhat when hot?

Switch/solenoid are working fine as the PSE note at WOT is unchanged (as far as I can tell) whether the mufflers/engine are cold or hot. It really is only noticeable when accelerating from idle, up through to say 4K rpm - The sound is distinctively different depending on whether the car is cold or hot.

Edited by ZX7R

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Maybe time to clean the front radiators.

PSE should not change it's tone if no wires are connected - because the mechanical valves are always open when there is no electronic control.

Hi Loren,

Checked my radiator ducts and they were both partially occupied by leaves. Used a vacuum cleaner to remove the leaves and radiator fans have not cut in at all over the last couple of days.

Many thanks,

Dave

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I'll temporarily disconnect/seal the vacuum lines at the solenoid to see if this has any effect to try and isolate the issue.

Just for everyone's reference I disconnected the vacuum line(s) from the solenoid leading to the mufflers and this cured the issue I was having.

Looks like for some reason my solenoid is 'leaking' vacuum (through to the muffler valves) when the engine bay gets hot! - I have reconnected the vacuum line back to the solenoid a couple of times to confirm the original problem - and sure enough when my engine bay heats up my PSE system is a lot quieter between 0 and 4K rpm - with the vacuum line disconnected the PSE note under 4K rpm does not alter at all with a hot or cold engine.

Note that I have a dash mounted switch to manually control my PSE valves and I have bypassed the speed sensor wiring at the relay cradle.

Edited by ZX7R

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Looks like for some reason my solenoid is 'leaking' vacuum (through to the muffler valves) when the engine bay gets hot!

So, are you going to replace the solenoid, or simply disconnect the vacuum?

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Gents,

I had a PSE on a previous 996 (1999) and pursched a newer 996 (2003) recently with a PSE installed (without wiring) and have noticed the following:

Occasionally, when I am sitting in traffic, I will hear what I think is the cooling fans cutting in (after I've been stationary for a while) and if I then blip the throttle, the PSE's are momentarily much deeper in sound.

My PSE sounds great in normal use, but when the above occurs, is f**king awesome!

Anyway, I just wanted to check if this was normal and if anyone has a more technical explanation of why this happens.

Many thanks in anticipation of a response.

Regards,

Dave

This happens to mine. It's usually first thing in the morning you drive for a bit and come to a stop light. The fan kicks in for a bit and if you happen to move off at the same time, the exhaust sounds really "gurgly". I personally don't like the sound, but this is normal operation.

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So, are you going to replace the solenoid, or simply disconnect the vacuum?

I'll probably throw on a vacuum gauge on the output (switched) side of the solenoid to verify that when its hot it does allow vacuum through - If that's definitely the case then I'll just purchase a replacement solenoid as its easy to access and swap out (only a 5min job).

I have not noticed any change in note in my PSE when my fans are or are not running though, and there is no physical or electrical connection between these two systems so I cannot see how the note can change which is odd.

I wonder if it could be possible that when the fans cut in - the engine timing etc is also being altered slightly by the ECU which may (possibly?) alter the exhaust note - just guessing here... But like I said, I have not noticed this on my car.

Edited by ZX7R

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