Ignition Timing Control System: Notes
Programmed ignition used in this engine provides optimum control of ignition timing. The ECM determines the timing in response to engine speed and manifold vacuum pressure. The input signals are transmitted by the CYP/CKP sensor, TP sensor, radiator fan control sensor, and MAP sensor. This system is capable of setting lead angles with complicated characteristics that cannot be provided by conventional governors or diaphragms.
The ECM has settings for optimum basic ignition timing based upon engine speed and intake manifold pressure. With input signals from the sensors, the system determines optimum timing for ambient conditions and sends voltage pulses to the ICM. Ignition timing is fixed at 5° BTDC for cranking. The cranking is detected by the CYP sensor (cranking RPM) and starter signal. At warm-up, the ECT sensor input is used to adjust lag angle according to warm-up conditions to balance between operating performance and exhaust gas level.
When idling, the CKP/CYP sensor and MAP sensor inputs are used to control ignition timing by compensating according to the idling speed. When engine coolant temperature is high, optimum lead or lag angle timing adjustment is applied. As part of the OBD II misfiring detection system, each of the ignition coils has a built in spark plug voltage sensor. The sensor detects the long duration high voltage which occurs during unfavorable combustion or misfiring. See Fig 1 and Fig 2 .