Exhaust Valve Vacuum Information

Smudgemanuk

Smudgemanuk

Zorg Guru (II)
British Zeds
Joined
Dec 1, 2024
Points
104
Location
Bicester, Oxford
Model of Z
2.8l TU pre-facelift z3
I am trying to get the exhaust valve working on my 98 z3 (I know people have said not to bother, but I quite like the idea of it!)

The vacuum pipe that comes off of the vacuum tank goes into a right angle piece, and then enters into the fuse box??

This confuses me quite a bit, and makes the path of this pipe to the back of the car hard to trace.

The pipe entering the fuse box can be seen in the photo below:
(the right angle joiner than can be seen in the diagram below this photo, is just before this pipe enters the fuse box)

IMG_7570.jpg


Part Diagram below to help:
Number 6 right angle T piece is just before the pipe enters the fuse box
Screenshot 2025-04-29 at 20.22.33.png


My questions are:

Is the vacuum actuator in the fuse box?
If not what is in there?
Is it difficult to get to?
Is there anything I should look out for?
Where does this pipe exit?

Thanks Chris
 

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I have looked into this a fair bit still dont have an answer.

So easy way to check all the vacuum pipes and valves.

First make sure flap actually moves you should be able to put your hand up above the pipe find actuator rod out of vacuum unit makes sure all moves.

Next remove left side boot trim look down you will see the actuator ( 5 in pic above) and the 2 vacuum lines plugged into it one from front and one to flap unit on exhaust.


When the engine is running you should have permanent vacuum on the pipe from the front ( saves check on everything forward of boot)
Now if you take the 2 vacuum pipes bypass the solenoid and join them
With the engine running that should then shut the flap and keep it shut which lets you know all vacuum side ok.

So next obvious choice was faulty solenoid in boot as that is what switches the vacuum to allow flap to open and close
So you check the part number discover common used vacuum switch still used on current models as things like egr vacuum control so readily available around £30 so bought one fitted still doesn't work.

Now the solenoid has 2 wires one should be an earth and the other will be the pulse live to switch the solenoid position.
Can't find where the live runs to and also cand find anything about what tells the car to switch the solenoid open and closed.
So gave up again and still have stuck open.
Stephen.
 
Thank you Stephen for the information above, much appreciated.

I think the next idea is to follow the same process you did and see what happens!

Just to confirm, does your vacuum line also run through the fuse box?

Did you replace/get at any of the exhaust valve vaccum pipes forward of the boot and before the fuse box?

I am rather keen to replace any and all vacuum lines on my car as the ones I found in my engine bay were more holes than pipe!

Chris.
 
With engine running i had good constant vacuum in boot at solenoid from pipe at front and when the 2 pipes joined flap shuts and stays shut so didn't really persue the route of the hose as far as i was concerned vacuum side of things was functional the problem lay elsewhere.
Stephen.
 
If it helps, the flap opens at about 2500rpm so the signal to switch the solenoid probably originates from the ECU.
 
Stevo7682 said:
With engine running i had good constant vacuum in boot at solenoid from pipe at front and when the 2 pipes joined flap shuts and stays shut so didn't really persue the route of the hose as far as i was concerned vacuum side of things was functional the problem lay elsewhere.
Stephen.
Click to expand...
Yeah I thought that might be the case
 
If all else fails I might put a Arduino controlled solenoid on it and bypass the ECU doing it
But we will see
 
@Eddie Zedder I am following this thread with interest. I have chatted with @Stevo7682 often on the workings of this exhaust flap. So what actually moves or alters in order to change the engine note at 2500rpm .
 
My understanding is that there is a constant vaccum in the pipe that run from the engine bay to the exhaust value. However there is a solenoid in the boot that when open, it allows the vacuum to pull on the valve, closing it. However when the solenoid shuts it stops this vaccum from getting through so the springs on the valve, holds the flap open. I think the solenoid is just controlled by electrical signal
 
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I figured out why the line ends up in the fuse box!
Because it travels with the main loom, through the car. And the main loom ends up both in the boot and in the fuse box!
 
BillyB said:
@Eddie Zedder I am following this thread with interest. I have chatted with @Stevo7682 often on the workings of this exhaust flap. So what actually moves or alters in order to change the engine note at 2500rpm .
Click to expand...
As @Smudgemanuk says, with the engine running there is a constant vacuum to the valve that keeps it shut. There is an electronic pulse generator for the tacho (on the crankshaft I believe) that feeds engine speed information to the ECU. At 2500rpm the ECU will send a signal to operate the solenoid to shut off the vacuum and the valve will open hence the change in exhaust tone. If the vacuum fails i.e. split pipe, the valve will failsafe to the open position, hence the valve is always open when there is no vacuum i.e. engine off. if the valve is closed when there is no vacuum it must be stuck.
 
Thanks for info, what I am getting is , flap open engine off , flap still open engine running , good vacuum to solenoid but solenoid shut , join both vacuum hoses together and flap shuts ok. Solenoid not working or no volts / message to keep it closed until 2500rpm , how then do I still get a change of engine tone at 2500rpm .All info appreciated
 
Could be the Vanos kicking in that changes the tone. I think this happens around 2900rpm though.
 
Ah, that would explain it possibly, it's definitely about the 2500 area. Ok going to get the solenoid and the feed checked sometime. Thanks for feedback.
 
BillyB said:
Ah, that would explain it possibly, it's definitely about the 2500 area. Ok going to get the solenoid and the feed checked sometime. Thanks for feedback.
Click to expand...
No worries, happy to help.
 
Just found this on Pistonheads.

That is called the Active Exhaust System Actuator (AESA). The AESA consists of the following:

Exhaust flap with vacuum actuator
Solenoid actuator valve
Vacuum reservoir with check valve
MS 41.1 control module
The electrical function of the exhaust flap operation is controlled by the MS 41.1 module.

At idle speeds, up to 2500 RPM: the exhaust flap is closed with vacuum applied to the actuator. This causes the exhaust gas to pass through the long resonator pipe, reducing the low frequency noise that is generated.

Above 2500 RPM: the exhaust flap opens. This allows the exhaust to pass through the short pipe which maximizes the back pressure effect to provide the best performance.

In the event of electrical or vacuum failure the flap will rest in the open position providing maximum exhaust throughput.
 
Right guys having read up to date my question now is going to be does the Zed 3 2.8 m52 tu have a Ms 41.1 module and if so any takers on location.
Everything works on mine i have the multiplug and a length of wiring if i start my zed flap is open ( vacuum checked and new solenoid) if i unplug the car loom and plug mine in connect to a power supply i can ( with engine running) open and shut the valve by energising the solenoid so for me im certain the issue is the live signal to the solenoid.

Stephen.

Edit .
Scratch that just looked up what the
MS41.1 module is
So its the DME engine control unit so for me if issue stems back to that then its game over not worth pursuing further.

Stephen.
 
Hi Stephen, that's the assumption I have that the power is not getting to the solenoid to make it open therefore shutting the flap. Keep going lol
 
Checked mine today out of curiosity, it appears I have the same problem. Ran engine but flap stays open. Vacuum is there, flap works when connected directly, pulled the solenoid out and put 12v across it and that also works as it should. I'm wondering if there is some other trigger to close it, maybe engine up to working temperature or something similar. Not had it out for a long run so will have to test that theory. Also planning to rig up a test light from the solenoid plug onto the dash to see if it lights up if and when the DMS signal is there.
 
RIGHT!

I followed the same steps as most others have above and got the exact same results. GRR

Stock: Valve stays open
Pipes Joined: Valve Closed
Solenoid test: Works fine

Surely the only other thing it could be is a dodgy feed! But it can't be if it is happening to all of us. Surely!

I like the logic of, engine has to be at working temp, or other variation of that

Too bad I can't drive my car till July to test it !

If someone else could that would be much appreciated
 
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