Electronic Ignition (EI) System Description: Operation

The powertrain control module (PCM) uses reference pulses from the crankshaft position (CKP) sensor in order to determine the engine speed. The PCM cannot operate the ignition system or the fuel injectors without the engine speed signal from the CKP. The PCM controls the ignition timing by controlling the ignition coils.

Each ignition coil has a built-in ignition module that controls the current flow in the primary coil winding. When the current flow is interrupted, the electrical field around the primary coil collapses and a high voltage is induced in the secondary coil. The secondary coil voltage travels from the coil output terminal, through the spark plug boot, and across the spark plug gap to the engine block. As a fail-safe function the ignition control module sends an ignition confirmation signal back to the PCM whenever the primary field collapses.

The camshaft position (CMP) sensor input is used to detect an engine misfire. The PCM also uses the CMP sensor signal as an input for modifying the fuel injection timing and for modifying the ignition timing.

The PCM receives information on the engine status from various engine sensors and then selects the most appropriate ignition timing settings from within the PCM's programming. The following are the most important inputs for determining ignition timing requirements:

• The engine speed
• The throttle position (TP)
• The intake air volume
• The engine coolant temperature (ECT)
• The knock sensor (KS) input

Fig 1: Crankshaft Position (CKP) Sensor Component View

Courtesy of GENERAL MOTORS CORP.

The CKP sensor reluctor (3) has 34 teeth and is mounted on the crankshaft behind the timing chain cover and the crankshaft pulley. When the crankshaft rotates, the CKP sensor signal rotor teeth pass by the CKP sensor (2) causing a fluctuation in the sensors magnetic field. The fluctuation in the magnetic field induces a voltage in the CKP sensor circuitry that corresponds to every 10 degrees of crankshaft rotation. The reluctor has one wide tooth (1) that indicates top dead center (TDC) of the number 1 cylinder. With the information that the PCM receives from the CKP sensor, the PCM determines engine speed and crankshaft position.

Fig 1: Intake Camshaft, CMP Sensor Signal Rotor And CMP Sensor

Courtesy of GENERAL MOTORS CORP.

The CMP sensor signal rotor (2) is part of the intake camshaft (1) and has 3 teeth located on the outer circumference. When the CMP sensor signal rotor (2) rotates past the CMP sensor (3), electrical signals are generated. The AC signals that are generated by the CMP sensor are sent to the PCM.