Closed Loop Mode

In this mode, the ECM sends an electrical signal to the vacuum control or M/C solenoid based on input from the oxygen sensor and other data sensors. In closed loop, the air/fuel mixture is controlled directly by the ECM in response to oxygen sensor signals.

During any operational mode, the ECM maintains the current duty cycle being used within its memory; for either idle or off-idle operation. When the ECM receives a change in idle position, as signaled by the Idle Position Switch or by the Vacuum Switch, the ECM retrieves data from its memory to operate the engine at the duty cycle last recorded for optimum operation.

After the initial change in idle position, ECM controls the system in 1 of the 4 operational modes. The ECM also controls the operation of the slow cut solenoid valve incorporated in the carbu- retor. When the ECM senses a coasting condition, it opens the circuit to the slow cut solenoid valve (engine speed above a predetermined value).

The circuit to the slow cut solenoid valve is cut off only when the vacuum signal of the vacuum switch is below specified vacuum and the engine speed exceeds a predetermined speed.