Operation

Ignition System:

The PCM uses reference pulses from the Camshaft Position (CMP) sensor in order to determine engine speed. The PCM cannot operate the ignition system -or the fuel injectors - without the engine speed signal from the CMP.

The four ignition coils supply spark to each engine cylinder, or spark plug, at precisely the right time. When the PCM sends a signal to the ignition module that is built into the ignition coil, the module responds by interrupting the current flow in the primary coil windings. Interrupting the current flow causes the electrical field around the primary coil to collapse, inducing a high voltage in the secondary coil. The secondary coil voltage travels unhindered to the spark plug, through the high voltage output terminal and boot assembly.

The PCM also uses the CMP sensor signal as an input for control of the fuel injectors and ignition timing. The Crankshaft Position (CKP) sensor signal is used by the PCM for engine misfire detection.

The PCM provides three modes of ignition timing control. Each ignition timing mode provides the most suitable spark advance for optimal engine performance. The following are the 3 modes of ignition timing control:
^ Initial timing control - The initial timing control ignition advance provides better starting performance of the engine at start-up, when engine speed is less than 500 RPM. The PCM sets initial ignition timing advance to 5 degrees Before Top Dead Center (BTDC).
^ Basic timing control - After the engine is running, ignition timing advance is determined by combining basic timing control and compensating timing control. Basic timing control ignition advance is based on engine coolant temperature, engine speed, and intake air volume. The ignition timing advance value, calculated from the Engine Coolant Temperature (ECT) sensor, the CMP sensor, and the Mass Air Flow (MAF) sensor input, is added to the 5 degrees initial advance, and modified by the compensating timing control value.
^ Compensating timing control - The compensating timing control ignition advance is added to the basic timing control value. The following are the most important factors in calculating the compensating ignition advance value:
- Knock sensor input
- Engine coolant temperature
- Intake air temperature
- Engine load

Ignition timing on the 2.0L engine is adjustable. The CMP sensor housing can be repositioned, much like a distributor, in order to adjust the base ignition timing setting. A scan tool must be used to request that the PCM operate the ignition system in the ignition timing check mode. Refer to Ignition System Timing Adjustment Procedure.