Ignition System: Description and Operation

Description

Ignition Timing Control
The programmed ignition system on this engine provides optimum control of ignition timing. A microcomputer determines the timing based on information about engine speed and intake manifold vacuum, which is transmitted by signals from the CKP/CYP sensor, throttle position (TP) sensor, engine coolant temperature (ECT) sensor, and MAP sensor. This system, which is not dependent on a governor or vacuum diaphragm, is capable of providing ignition advance characteristics which cannot be provided by conventional governors.






Basic Control
The PCM has stored within it the basic ignition timing for operating conditions based upon engine speed and intake manifold vacuum. With the compensating signals from sensors, the system determines optimum ignition timing and duration for ambient conditions and sends voltage pulses to the ICM.






Control at Start
Ignition timing is fixed at 5° BTDC for cranking. The cranking is detected by the CKP sensor (cranking rpm) and starter signal.

Misfiring Detection
As part of the OBD II misfiring detection system, each of the ignition coil has a built-in spark plug voltage sensor. This sensor detects the long duration high voltage which occurs in case of unfavorable combustion or misfiring.