Excessive Black Smoke
Several things could be causing black smoke in your 6.0 Powerstroke:
Cause: Clogged EGR valve (causing too much backpressure into the cylinder)
Solution: Clean or replace the EGR valve.
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.
Cause: Stiction in injectors
Solution: Treat the oil system with Stiction Eliminator.
The EGR valve can be removed and cleaned out in some instances, but it may need to be replaced. The 6.0 Powerstroke was the first Ford diesel to have an EGR system, and they were prone to failure. To stay ahead of the game, clean out your EGR on a regular basis. There are delete kits available, but these will cause your truck to fail an emissions test, potentially resulting in a hefty fine. Excessive black smoke can also be caused by a dirty air filter (causing a restriction in the air inlet system). Check the air filter, and replace it if needed.