Why is there a gasoline smell in the exhaust when starting a cold engine?

[DiAlaina]

It is related to the control method of the engine injection system. The specific explanation is as follows: 1. Cause: The injection system has two control methods—open-loop control and closed-loop control. During open-loop control, the system does not reference the data from the oxygen sensor. For a period after the vehicle starts, the engine injection system operates under open-loop control. The high concentration of the air-fuel mixture results in unburned gasoline being expelled with the exhaust, which is why there is a gasoline smell in the exhaust. 2. After the temperature rises: Once the vehicle's temperature increases and the oxygen sensor and catalytic converter function normally, the engine injection system switches to closed-loop control, maintaining the air-fuel ratio at around 14.7:1. This leads to cleaner exhaust emissions, and the gasoline smell in the exhaust naturally disappears.