What Causes the Unpleasant Smell from a Car's Exhaust Pipe?

[AaronRose]

Car exhaust pipe emits unpleasant smell due to the following reasons: Rich Air-Fuel Mixture: This situation occurs when the car's combustion is incomplete, resulting in an overly rich air-fuel mixture. Oxygen Sensor Failure: It could also be due to a malfunctioning oxygen sensor in the catalytic converter, preventing the engine from accurately detecting the oxygen concentration in the exhaust pipe, leading to an incorrect air-fuel ratio. Oxygen Sensor Malfunction: An oxygen sensor malfunction can also cause foul-smelling exhaust and increased fuel consumption. The oxygen sensor continuously monitors the oxygen content in the exhaust. When the oxygen content is too high, the sensor signals the ECU to reduce the vehicle's fuel injection, making the engine combustion more complete. Therefore, when the oxygen sensor fails, the engine's combustion efficiency cannot be improved, and an overly rich mixture will inevitably lead to an increase in exhaust odor.