[airjoe]

Hi, so i put M5 mufflers on my 550. For the first few days, all was good - played around with valves tied open and hoses plugged vs connected; and decided i like it quieter - ie with the hoses connected and letting the valves open up at higher load/RPM.

Well, a few days in, i notice the valves are open all the time. Idling, cruising at 40mph (can tell because of the slight drone), etc.

What would cause the valves to stay open? They are closed when the car is shut off. As i understood the system, they are opened on demand by a vacuum pump (???), and therefore should NOT be open all the time, especially at idle.

Looking for ideas...