Aug 6 2010
Black smoke from a vehicle¡¦s engine signals over-fuelling and the black colour results from the carbon particles that are unburned during gas combustion. Over-fuelling rarely occurs in petrol engines having fuel-injection feature, and the black smoke from such fuel-loaded engines can be due to defective sensors such as the mass air flow (MAF) sensors and oxygen sensors.
The oxygen sensor that is placed in the exhaust gas pathway plays a major role in fuel control process. By using signals from oxygen sensor, computer maintains a balanced equilibrium in the fuel mixture, maintaining it thick or thin according to the sensor readings. The sensors should get heated to a minimum of 250°C before it starts working and the heating time is reduced with the help of a heating system placed internally in many sensors. The normal longevity of an oxygen sensor is from 50,000 to 80,000km. Upon carbon coating or contamination by silicone it gets exhausted soon, requiring highly expensive replacement.
The MAF sensor is located in the intake air passage which is separated by air cleaner and various inlets. The sensor sends information to the engine¡¦s computer electrically and measures the volume of air that reaches the engine continuously. The computer then maintains the ideal quantity of petrol that has to be injected, in proportion with air/fuel ratio and balances the equilibrium of fuel mixture that was sensed by oxygen sensor.
If the oxygen sensor has not gained proper heat enough to start its work or it is defective, computer seeks data from the MAF sensor so as to maintain the fuel mixture balanced. Reports say that the MAF sensor becomes defective due to fumes or smoke in the air ingested.
Source: http://www.sowetanlive.co.za