Run Mode

PURPOSE
When the following conditions are met, the engine goes into closed loop operation. When operating in closed loop, the Electronic Control Module (ECM) determines the air/fuel ratio (injector pulse rate, or Mixture control dwell on C-3 systems) based on signals from the Oxygen (O2) sensor. This allows the air/fuel mixture to remain close to the optimum 14.7:1 ratio.

OPERATION
The Run Mode consists of two separate operating conditions; open loop and closed loop. The engine operates in open loop when it is first started and RPM is above 400 RPM. During open loop operation, the ECM disregards the oxygen sensor signal and determines air/fuel mixture based on the inputs from the coolant and Mass Air Flow (MAF) or Manifold Absolute Pressure (MAP) sensors.

Closed Loop Operating Conditions
The engine will continue to operate in open loop until the following conditions are met:
^ The oxygen sensor has varying voltage output, indicating it is hot enough to operate properly.
^ The coolant sensor is above a specified temperature.
^ A specific amount of time has elapsed since the engine was started.

NOTE: The specified values for conditions mentioned above vary from model to model, and are stored in the ECM PROM.