this is interesting may be of help
http://www.autoguide.com/auto-news/2015/04/what-does-the-smoke-from-my-exhaust-mean-.html
What does BLACK smoke from my exhaust mean?
Black exhaust smoke means the engine is burning too much fuel. The first think you should check is your air-filter and other intake components like sensors, fuel injectors and the fuel-pressure regulator. Other reasons could be a clogged fuel return line. Black smoke is usually the easiest issue to diagnose and fix, but burning unnecessary fuel will definitely affect your fuel economy, so don’t think of avoiding this one to save money, it won’t work.
Any smoke coming from your car’s exhaust pipe is a sign that your car is in distress. Pay attention to what it needs to ensure more miles for your vehicle.