Excessive Black Smoke
Several things could be causing black smoke in your 5.9L Cummins:
Dirty air filter (causing a restriction in the air inlet system) Check the air filter and replace it if needed.
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) Treat the fuel system with Diesel Extreme.
If you have any questions, feel free to contact one of our diesel experts.