The electronic ignition system on the 2.2 L dual overhead cam (DOHC) engine provides spark energy to ignite air/fuel mixture necessary for combustion. The powertrain control module (PCM) controls spark under all engine running conditions. The system components include: PCM, electronic ignition (EI) module/ignition coil housing/spark plug boots, spark plugs and knock sensor.

The spark dwell (On-time) and degrees of spark advance are dependant upon engine speed, manifold absolute pressure (MAP), and engine coolant temperature (ECT). The PCM can vary spark advance from 60° BTDC to 3° ATDC under all engine running conditions when no spark knock is present.

The primary function of EI module is to charge and discharge coil packs based on PCM control. The PCM has two control circuits, one for 2/3 coil and the other for 1/4 coil. The PCM uses a high control signal of near 5 volts to charge up coil and a low control signal of near 0 volts to discharge coil. If coil is charged and control signal is low, coil will fire through its secondary towers. The secondary voltage across spark plug can reach a maximum of 37,000 volts.

The secondary current for a coil always travels in same direction and in a series type circuit. For example, when PCM fires 1/4 coil, current will flow out of #1 coil tower, to #1 spark plug boot, to #1 spark plug, through block, up through #4 spark plug, through #4 spark plug boot and back to #4 coil tower. Therefore, when a coil fires, both cylinders tied to it fire simultaneously. If one of the boots/plugs were to open, the other mating cylinder would still fire out of its coil tower because circuit would be completed through EI module bolts.

In order to determine when to fire a cylinder PCM uses signal from crankshaft position (CKP) sensor. The crankshaft has 7 machined notches, 2 of which are close together representing a double pulse. The PCM uses this double pulse to identify cylinder #4 top dead center (TDC). However, the PCM still has to identify position of camshaft in order to initiate sequential fuel injection. This is accomplished by use of Compression Sense Ignition.

The 2.2 liter engine utilizes Compression Sense Ignition, which eliminates need for a camshaft position sensor. The EI module has sensing circuitry that detects when cylinder #1 or cylinder #3 has fired on its compression stroke and relays this information to PCM. The PCM can then correctly synchronize fuel injectors for sequential fuel injection. If PCM cannot detect a correct cam signal, it will default to using alternating synchronous double fire (ASDF) method to inject fuel.

The EI module uses capacitive pickup plates located above 1/4 and 2/3 coils to determine when cylinder #1 or cylinder #3 has fired on compression. These plates are used to differentiate polarity and voltage amplitude difference between #1 and #4 or #2 and #3 secondary ignition circuits. Since each coil tower is of opposite polarity and waste spark (2-4 kV) generally fires before compression spark (10-25 kV), the module can determine when cylinder #1 or #3 is on compression. When EI module detects a positive to negative polarity sequence and a high negative voltage spike, it will supply 5 volts to PCM on cam signal circuit. The PCM knows which cylinder has just fired on its compression stroke when this transition occurs.

The EI module, however, cannot always detect when cylinder #1 or #3 has fired on compression. These occurrences include:

The scan tool displays cam signal to PCM as CALC. COMPRESSION OUTPUT. Since engine firing order is 3-4-2-1, a normal compression output bit pattern will be 00000110 or 00001001 during engine crank, idle, cruise or accel. If a fault is occurring in ignition system or if a cylinder is loosing compression, the bit pattern will intermittently change or stray from normal pattern. This bit pattern can be used to determine cause of a misfire. Refer to DTC P0300 for different bit patterns vs. a specific failure mode.

The PCM uses knock sensor to determine when spark knock exists and can retard timing up to a maximum of 15°. The knock sensor is a piezoelectric flat response (wide resonant band) device that produces an AC voltage of different amplitude and frequency based on engine mechanical vibration. The amplitude and frequency are dependent on level of knock the sensor detects.

The PCM learns an average noise level from knock sensor (based on a calibrated average) and monitors signal to verify that it stays above a minimum value. The knock sensor signal is only used during top dead center combustion event of firing cylinder. When in a combustion event, PCM filters knock signal and compares it to normal calibration noise level for that RPM. If PCM has determined that knock is present during combustion event, it will retard timing on next firing cylinders until knock is eliminated. The PCM will always try to work back to a zero compensation level or no spark retard.

The Scan tool displays actual amount of spark advance degrees and actual amount of spark retard degrees as SPARK and SPARK RETARD CYL #1-4. If excessive spark knock is detected, retarding of timing will cause a reduced power condition.