Have you done a boost leak test? Blowing out black smoke and knocking simultaneously is a good sign of a good boost leak. Say you've got the boost set at 16psi, but you have a good leak at anything above 9psi, the turbo will spool to all hell to maintain 16psi with the leak, when in actuality it could be spitting out more like 24psi. The constant loss of boost will indeed cause the black smoke, and the overworked turbo shoving superheated air into the engine will cause knock at the same time. Thats how I cracked my #2 ring lands. Anything over 10psi and I could audibly hear detonation, but I had tons of fuel. Turns out when I tested it, I couldnt get the system to hold more than 8psi with a 30 gallon compressor working its ass off. So, I'd check for leaks.