Black exhaust smoke simply means that your engine is burning too much fuel. Engines need both fuel to burn and oxygen to burn it with. If there is too much fuel in the combustion chamber and not enough oxygen to burn it with, it can cause black smoke to come from your exhaust.
Clogged air filters with dust blocking the air filter.
With dust blocking the air canaltaronja.cat filter, there are chances that sufficient air amount is not reaching the cylinder. As a result, more fuel is being burnt. And ultimately this causes black smoke from exhaust irrespective of the fact that the fuel injectors are working properly.
Damaged fuel injectors
In this situation, even the amount of air is insufficient for the combustion of fuel due to blocked injectors (and the few opened ones inject only fuel). As a result, solid carbon is formed from the fuel not burnt, which is emitted as black smoke from the tailpipe of the car.
Faulty Massive Air Filter (MAF) sensors.
Over time, the sensor gets covered with a fine dust that escapes the air filter. When this happens, the electronic controller receives false air-flow information leading to incorrect fuel management. This can also lead to black smoke. To solve this look for “MAF Sensor Cleaning Fluid”.
Bad EGR valve.
The EGR helps to re-circulate the engine emission by returning them to the combustion chamber and not sending them directly to the exhaust emission system. The carbon chucks could clog your EGR valve, which will result in loss of power, fuel inefficiency and emission of black smoke from your exhaust.
Damaged piston Rings.
If there is any problem with the piston rings, the engine oil starts flowing into the combustion chamber. The combustion of the mixture of this engine oil and the fuel delivers black smoke.
Over-fueling is the primary cause of black smoke from the exhaust of a heavy-duty diesel engine. Excessive oil consumption due to worn valves and valve stem seals, worn or stuck/sluggish rings from deposits, and worn cylinder liners contribute to black smoke.