Electronic Ignition

The electronic ignition system on the 2.2 L Dual Overhead Cam (DOHC) engine provides spark energy to ignite the air/fuel mixture necessary for combustion. The Powertrain Control Module (PCM) controls spark under all engine running conditions. The system components include: the 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 dependent 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.

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

The secondary current for a coil always travels in the same direction and in a series type circuit. For example, when the PCM fires the 1/4 coil, the current will flow out of the #1 coil tower, to the #1 spark plug boot, to the #1 spark plug, through the block, up through the #4 spark plug, though the #4 spark plug boot and back to the #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 the circuit would be completed through the EI module bolts.

In order to determine when to fire a cylinder. The PCM uses the signal from the 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 the position of the camshaft in order to initiate sequential fuel injection. This is accomplished by the use of Compression Sense Ignition.

COMPRESSION SENSE IGNITION (CSI) - The 2.2 liter engine utilizes Compression Sense Ignition, which eliminates the 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 the PCM. The PCM can then correctly synchronize the fuel injectors for sequential fuel injection. If the PCM cannot detect a correct cam signal, it will default to using the Alternating Synchronous Double Fire (ASDF) method to inject fuel.

The EI module uses capacitive pickup plates located above the 1/4 and 2/3 coils to determine when cylinder #1 or cylinder #3 has fired on compression. These plates are used to differentiate the polarity and voltage amplitude difference between the #1 and #4 or #2 and #3 secondary ignition circuits. Since each coil tower is of opposite polarity and the waste spark (2-4 kV) generally fires before the compression spark (10-25 kV), the module can determine when cylinder #1 or #3 is on compression. When the EI module detects a positive to negative polarity sequence and a high negative voltage spike, it will supply 5 volts to the PCM on the 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:
^ During deceleration
^ Very low engine load conditions when engine is running
^ If a primary/secondary ignition problem occurs

The Scan tool displays the cam signal to the PCM as CALC. COMPRESSION OUTPUT. Since the 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 the ignition system or if a cylinder is loosing compression, the bit pattern will intermittently change or stray from the normal pattern.

This bit pattern can be used to determine the cause of a misfire. Refer to DTC P0300 for different bit patterns vs. a specific failure mode.

SPARK KNOCK CONTROL - The PCM uses the 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 the level of knock the sensor detects.

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

The Scan tool displays the 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, the retarding of timing will cause a reduced power condition.