I am on my 3rd BMW straight - 6 (Z4 MC, 335i, 128i), I will say that the engine is fantastic. However, as far as being easy to work on...I disagree. Partly due to the location but, mostly due to the specialized tools required.
From the picture, I could not tell if the smoke was coming from inside the cat or the heat shield around the cat.
1. smoke is coming from AC drain that is leaking on cat
2. the weld on the cat is broken and exhaust is leaking out
3. head gasket leak and coolant is getting into the...
Without any codes, I would think that maybe you have coolant leak that is getting into the cylinders and is causing a misfire and the coolant is leaking out of the cat.
Check the oil for coolant
Buy a iCarsoft LR II scanner and check the codes
I should point out that you will probably need to do a software update on it the device (unless seller has already did one), not very hard but you will need a laptop or some device that accepts a USB port and is connected to internet
It shows the fault code and generic description of fault code, you can also access the SLABs unit to read and clear codes, turn on and off some accessories, and of course monitor real time data.
The only draw back for me is that it is slightly bulky and does not like to stay connected. I...