Excessive Black Smoke
Several things could be causing black smoke:
Cause: Dirty air filter (causing a restriction in the air inlet system)
Solution: Check the air filter, and replace it if needed.
Cause: Incorrect fuel spray pattern or extra fuel dripping out of the injector (causing the ratio of fuel to air in the combustion chamber to be too high)
Solution: Treat the fuel system with Diesel Extreme. Treat the oil system with Stiction Eliminator.