Electronic Ignition (EI)

The Electronic Ignition (EI) system is responsible for producing and controlling a high energy secondary spark. This spark is used to ignite the compressed air/fuel mixture at precisely the correct time. This provides optimal performance, fuel economy, and control of exhaust emissions. This ignition system uses one coil for each pair of cylinders. Each pair of cylinders that are at Top Dead Center (TDC) at the same time are known as companion cylinders.
The cylinder that is at TDC of its compression stroke is called the event cylinder. The cylinder that is at TDC of its exhaust stroke is called the waste cylinder. When the coil is triggered both companion cylinder spark plugs fire at the same time, completing a series circuit. Because the lower pressure inside the waste cylinder offers very little resistance, the event cylinder uses most of the available voltage to produce a very high energy spark. This is known as waste spark ignition. The ignition coils and Ignition Control Module (ICM) are contained within one assembly. The ignition coil/ICM assembly is mounted in the center of the engine camshaft cover, with short boots connecting the coils to the spark plugs. The coil driver modules within the ICM are commanded ON/OFF by the powertrain control module (PCM).


Crankshaft Position (CKP) Sensor
The CKP sensor is a permanent magnet generator, known as a variable reluctance sensor. The magnetic field of the sensor is altered by a crankshaft mounted reluctor wheel that has seven machined slots, six of which are equally spaced 60 degrees apart. The seventh slot is spaced 10 degrees after one of the 60 degree slots. The CKP sensor produces seven pulses for each revolution of the crankshaft. The pulse from the 10 degree slot is known as the sync pulse. The sync pulse is used to synchronize the coil firing sequence with the crankshaft position. The CKP sensor is connected to the PCM by a signal circuit and a low reference circuit.

Ignition Control Module (ICM) and Ignition Coils
Each ignition coil is responsible for supplying secondary energy to a pair of spark plugs. The ignition control signals output by the PCM am amplified by the ICM in order to fire each coil. The spark events are triggered by the ICM, but the module has no influence on spark timing. The ICM is also responsible for detecting and supplying a Camshaft Position (CMP) signal pulse to the PCM to be used for sequential fuel injection. This ignition system does not use a conventional CMP sensor that detects valve train position. The ICM detects when either cylinder 1 or cylinder 3 has fired on the cylinders compression stroke using sensing circuitry integrated within each coil. The sensing circuit detects the polarity and the strength of the secondary voltage output, the higher output is always at the event cylinder. The ICM sends a CMP signal to the PCM based on the voltage difference between the event and waste cylinder firing energy. This system is called compression sense ignition. By monitoring the camshaft position and Crankshaft Position (CKP) signals the PCM can accurately time the operation of the fuel injectors.

Powertrain Control Module (PCM)
The PCM controls all ignition system functions, and constantly corrects the spark timing. The PCM monitors information from various sensor inputs that include the following:
^ The Throttle Position (TP) sensor
^ The Engine Coolant Temperature (ECT) sensor
^ The Mass Air Flow (MAF) sensor
^ The Intake Air Temperature (IAT) sensor
^ The Vehicle Speed Sensor (VSS)
^ The transmission gear position or range information sensors
^ The engine Knock Sensors (KS)

Modes of Operation
There is one normal mode of operation, with the spark under PCM control. If the CKP pulses are lost the engine will not run. The loss of a CMP signal may result in a longer crank time since the PCM cannot determine which stroke the pistons are on. Diagnostic trouble codes are available to accurately diagnose the ignition system with a scan tool.