What happens to oxygen levels during cranking when the TAC system operates correctly?

When the Throttle Actuation Control (TAC) system operates correctly during cranking, oxygen levels typically decrease slightly. This decrease occurs because, during cranking, the engine is not yet producing power, and the air-fuel mixture is drawn into the engine. The combustion process has not yet started, and the engine is effectively consuming air as it attempts to start.

The TAC system ensures that the throttle position is managed appropriately, which helps in regulating the intake of air and fuel. As the engine cranks, the fuel injectors may inject fuel into the combustion chamber, but without ignition, the air is mainly being consumed without being fully utilized, resulting in a slight decrease in oxygen levels in the intake manifold.

This dynamic reflects the engine’s need for oxygen for combustion, which is not happening until the engine begins to run after successful ignition. While other factors can influence oxygen levels, the proper functioning of the TAC system contributes to this controlled decrease in oxygen during the initial cranking phase.