MS43 Emission Optimized - Ignition Key Off
"Emission Optimized Ignition Key Off" is a programmed feature of the MS43 ECM.
After the ECM detects KL15 is switched "off", the ignition stays active (ECM Relay/voltage supply) for two more individual coil firings.
This means that just two cylinders are fired - not two revolutions.
This feature allows residual fuel injected into the cylinders, as the ignition key is switched off, to be combusted as the engine runs down.
When KL15 is switched "off" the ECM operating voltage is removed.
The ECM will maintain a ground to the Engine Control Module Relay for a few seconds to maintain ignition coil activation.
The HFM signal represents the amount of intake air volume. This input is used by the ECM to determine the amount of timing advance to properly combust the air/fuel mixture.
The Air Temperature Signal assists the ECM in reducing the risk of detonation (ping). If the intake air is hot the ECM retards the ignition timing. If the intake air is cooler, the ignition timing will be advanced.
As the throttle is closed, the ECM decreases the ignition timing if the RPM is above idle speed (coasting). This feature lowers the engine torque for deceleration. When the engine RPM approaches idle speed, the timing is slightly advanced to prevent the engine from stalling. The amount of advance is dependent upon the engine temperature and the rate of deceleration.
Knock Control allows the ECM to further advance the ignition timing under load for increased torque. This system uses two Knock Sensors located between cylinders 1, 2, 3 and between cylinders 4, 5, 6. Knock Control is only in affect when the engine temperature is greater than 35°C and there is a load on the engine. This will disregard false signals while idling or from a cold engine.
Based on the firing order, the ECM monitors the Knock Sensors after each ignition for a normal (low) signal.
If the signal value exceeds the threshold, the ECM identifies the "knock" and retards the ignition timing (3°) for that cylinder the next time it is fired. This process is repeated in 3° increments until the knock ceases.
The ignition timing will be advanced again in increments to just below the knock limit and maintain the timing at that point.
If a fault is detected with the Knock Sensor(s) or circuits, the ECM deactivates Knock Control. The ignition timing will be set to a conservative basic setting (to reduce the risk of detonation) and a fault will be stored. The "Malfunction Indicator Light" will be illuminated when the OBD II criteria is achieved.