Abstract: Through the dynamometer tests, variations of tailpipe emissions from a passenger car fueling with 93^# gasoline adding 10 different gasoline detergents were tested, respectively. Furthermore, a qualified physical detergent was chosen from the 10 detergents. The effects of energy saving and emission reduction were tested, and the detergency of the physical detergents in the engine deposits was also evaluated by engine disassembly test before and after driving about 12×10⁴ km with the additive. The results showed that the tailpipe emissions from the test vehicle would have different decrease if using qualified detergents. However, some emissions, such as HC and NO_x, might be increased after using unqualified detergents. The vehicle emissions of HC, CO, NO_x decreased obviously after using the physical detergent, approximately 14.3%, 13.6% and 16.7%, respectively. At the same time, the fuel consumption had a slight decrease of approximately 3.5%. There were some improvements in the deposits on the intake valves and cylinder covers after using the physical detergent. For example, the intake valve deposits (IVDs) decreased by about 6.8%. However, there was no obvious clarifying effect on the deposits on the piston crowns. The test also proved that major repair of the engine might result in the increase of fuel consumption and CO, NO_x emissions, while the vehicle emissions and the fuel consumption would be improved after the deposits being cleaned.