Can the muffler exhaust valve malfunction?

Hi, my name is Devin. I am an auto repair expert with the Car Genius team here at RepairPal. I’m sorry to hear you're having trouble with your 535i. The exhaust valve in the muffler, sometimes referred to as the flap or actuator, can malfunction. If it becomes stuck or fails to seal properly, it could allow unburned fuel or soot to exit, leading to a fuel smell and the black mark you see. A fuel smell and residue can also indicate an engine performance concern, so I recommend visiting a qualified shop to have things checked out. If you need more advice, have any other questions about your vehicle, or would like to get connected to a RepairPal Certified shop near you, we have you covered. Give us a call at 877-913-1554, and we will happily help you out!