Engine starting: During starting, when engine speed is below approximately 500 rpm (or when STA signal is high), spark advance angle (IGt signal) is fixed at initial timing. A Backup IC located in the ECU generates a reference timing signal which is output to the microprocessor and the IGt line to the igniter. The reference signal represents base timing and is calculated based on inputs from the G1 and Ne sensors.
Engine running: Once the engine starts, timing of the IGt signal is controlled by the microprocessor in the ECU. Based on inputs from various sensors, a basic and corrective advance angle are calculated. The final spark advance angle consists of the sum of the initial, basic, and corrective spark advance angles.
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