Run Mode

The Run Mode has two conditions, called "Open Loop" and "Closed Loop." When engine is first started and RPM is above 400 RPM, system goes into "Open Loop" operation. In "Open Loop", ECM ignores signal from Oxygen (O2) sensor, and calculates air/fuel ratio based on inputs from Coolant and MAP sensors.

The system will stay in "Open Loop" until the following conditions are met:

1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly (This depends on temperature.)
2. The Coolant Sensor is above a specified temperature.
3. A specific amount of time has elapsed after starting engine.

The specific values for above conditions vary with different engines, and are stored in PROM. When these conditions are met, system goes into "Closed Loop" operation. In "Closed Loop", ECM will calculate air/fuel ratio offset (injector on-time) based on signal from O2 sensor. This allows air/fuel ratio to stay very close to 14.7:1.