Electronic Control Module (ECM) Opel Campo I

Electronic Control Module (ECM)

The ECM controls the air - fuel ratio via the mixture control solenoid. This ECM controlling signal is continuously cycling the solenoid between on and off time (duty cycle) due to the signal voltages from the sensors.

1 cycle equals 50 ms. The percentage of the valve opening during 1 cycle is defined as 'Duty'.

By changing this duty cycle, the ECM controls the air fuel ratio.

The ECM controlling signal is selected from four operating modes as follows:

· Inhibit - A fixed control signal sent to the mixture control solenoid.

· Wide open throttle (WOT) - A pre - selected duty cycle based on engine speed.

· Open loop - A pre - selected duty cycle based on the following conditions:

- Engine speed less than 1600 rpm.

- Engine coolant temperature below approximately 40 °C / 104 °F.

- ECM timer less than 2.5 minutes.

Following a cold engine start, the timer within the ECM gives the oxygen sensor time to reach its operating temperature of 370 °C / 698 °F. Until the sensor reaches this temperature, it will send incorrect voltage signals to the ECM. The ECM timer uses the 2.5 minutes as the interval it takes for the O2 sensor to warm up.

The ECM is programmed to go into closed loop when all of the above conditions no longer exist.

· Closed loop - A calculated duty cycle based on oxygen sensor and other sensor inputs.

As the oxygen sensor voltage increases and passes the ECM threshold set point, the duty cycle changes so that the mixture control solenoid provides a leaner air / fuel mixture. The duty cycle also changes until sensor voltage decreases and passes through the ECM threshold set point. The mixture control solenoid duty cycle is again changed to provide a richer air / fuel mixture. By continuously trying to keep the O2 sensor voltage near this threshold set point, excess emissions are kept at a minimum. The selection of gain rates by the ECM is based upon engine operating conditions (engine rpm and oxygen sensor transition condition). At low speed conditions, gain rates are different for optimum air / fuel ratio control than those at middle or high speed conditions.

The duty cycle currently being used for idle / off - idle conditions is stored by the ECM in an adaptive memory. For example, the engine speed has increased from idle to off - idle, the ECM uses the last known duty cycle for operating the mixture control solenoid. As the duty cycle changes for various engine running conditions, the adaptive memory is updated. When the engine returns to idle, this updated duty cycle is stored and it will be used the next time the engine increases to off - idle.