Black smoke from the exhaust

I noticed the check engine light come on, the car began to use more gasoline than before, bringing out black smoke and i visited a mechanic. He said i should change the Electrical Control Unit, which i did, but the light was still on. i changed the injector fuel sprayers and the MAP sensor too, but the light is still on. i changed the ECU again, the light went off but black smoke is still coming out of the exhaust. I have tried to check if the car has any Oxygen Sensor, but could not find.
What can i do?