Fuel Control: Notes

The ECM, using input signals, determines adjustments to the air/fuel mixture in order to provide the optimum ratio for proper combustion under all operating conditions. One of 2 types of fuel control systems are used: throttle body injection or port fuel injection. These systems can operate in the "open loop" or "closed loop" mode. Description of these modes is as follows: Open Loop

When engine is cold and engine speed is greater than 400 RPM, ECM operates in "open loop" mode. In "open loop", ECM calculates air/fuel ratio based upon coolant temperature and Manifold Absolute Pressure (MAP) or Mass Airflow (MAF) sensor readings. Engine will remain in "open loop" operation until O2 sensor reaches operating temperature, coolant temperature reaches preset temperature, and a specific period of time has elapsed after engine starts.