Black smoke from the exhaust indicates that the fuel combustion is unbalanced. This means that there is too much fuel in relation to the air with which it is mixed inside the combustion chamber. Explanation: either there is not enough air, or there is an excessive amount of fuel.
If your vehicle has fuel injection, it may be that the sensors of the injection system are not well-situated. If any one of the sensors are malfunctioning or not well-situated, it’s possible that too much fuel is being injected into the cylinder, creating too rich of a fuel mixture, resulting in unbalanced combustion and therefore black smoke. In this case, you must bring your vehicle to a garage to have the injection system checked out and any faulty sensors replaced.
It may also be that the air filter needs to be changed. A dirty air filter prevents sufficient levels of air, and will consequently cause the air/fuel mixture to be too rich in fuel. Fuel consumption is therefore unbalanced and black smoke in the exhaust will occur.