cmyachtie

Question about a strange issue I have been having for some time now is that it appears my exhaust valve (near the tailpipes) which is vacuum operated to open at higher RPMs to reduce back pressure and reduce exhaust noise at idle, is opening up and I am puzzled why that would be happening.
It sounds like all of a sudden you have a hole in your muffler.....
First few times it happened was thinking it was just the wheel well noise from water but yesterday when I drove slowly thru a slushy road it also happened and I opened my window and while driving in neutral hit the gas pedal and it is definitely the exhaust.
It usually only last for up to 30 seconds and then goes away and am concerned maybe my intake is getting restricted and the increased vacuum opens the valve.
NE1 else experienced this?
Looking for some help here...
Thanks

dingolfing

Maybe your rubber hose connecting your vacuum pump to the exhaust valve has an air leak?

cmyachtie

You maybe right, will have a look,when car is dry and warm.....must be under car somewhere where the splashing water plugs the leak and restores the vacuum, as there is vacuum on that line all the time before the switch in the trunk.
BUT that still leaves me questioning why the flap is open at idle as it supposed to only open above 3000rpm.
Nevertheless good suggestion, thanks may just get to fix this finally

DanielFD

The flap is controlled by vacuum, but the solenoid in the trunk is what signals the flap to open and close (by opening a small valve that allows the vacuum to reach the flap). It is closed with no vacuum (unlike the e90 which is open with no vacuum). The ECU controls the opening of the flap. I remember there is a couple of reason the flap opens when i read about this, its not just about driving over 3000rpm.

cmyachtie

So today's weather here made it possible for me to have a good look at the muffler flapvalve and the vacuum arrangement no leaks and flap is functioning as it should so what I did is disconnected the switch for the valve (just connected the vacuum hose direct to the valve) and now I have a bit of a rumble all the time as I discovered my noise when driving thru heavy rain is much louder than just the flap opening and will see how that goes for now.
Only ran the engine a bit in the garage so will decide and keep an eye on things as it goes for the next few days., as I am still miffed at the loud V8 rumble I have been experiencing in a downpour.....sounds like all of a sudden having a broken muffler and then goes back to normal in a minute or so.