European E60 540i / 8cyl - noticed black residue in exhaust but only in one of the exhaust tips. Also, only one of the tips gets hot while driving and only that one actually produces visible exhaust. Should the exhaust actually function like this or is something wrong woth it?

Thanks.

As far as I know, the second exhaust flap opens only after a period of time (2-5 minutes?), after warming up the catalysator or catalyc converter. It has to do something with warming up the catalysator faster, because a cold catalysator can break quickly. Notice how smelly the exhaust is during a cold start (one flap open, catalysator probably off), but never when the engine is hot (both flaps open, catalysator working).

I've read about that somewhere but can't find the article anymore.

If the second flap never produces exhaust, there may be some issue. Try heating up the car by driving it hard for 15 minutes and have someone look at the exhaust while you push gas pedal in N/P mode (or capture it with a camera) to see if it's open.