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 sensor. 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 accelerator pedal position (APP)
• The intake air volume
• The engine coolant temperature (ECT)
• The knock sensor (KS) input

Fig 1: View Of CKP Sensor Signal Rotor

Courtesy of GENERAL MOTORS CORP.

The CKP sensor signal rotor (1) is an integral part of the crankshaft pulley (3) and is located behind the timing belt cover. 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 tooth on the crankshaft signal rotor. The rotor has 24 evenly spaced teeth, with two teeth missing, indicating top dead center (TDC) and producing 22 electrical pulse per revolution. CKP sensor A and CKP sensor B each provide position signals to the PCM. The PCM relies on the signal from CKP sensor A first, and uses the signal from sensor B only when sensor A is missing or unintelligible.

Fig 1: View Of Camshaft Position (CPM) Sensor

Courtesy of GENERAL MOTORS CORP.

The camshaft position (CMP) sensor (1) is fastened to the backside of the timing belt cover (2) of the left bank cylinder head. The cam gear (4) is attached to the left bank camshaft (3) inside the timing belt cover (2). The CMP sensor signal rotor is integral to the cam gear (4). The signal rotor has three unevenly spaced teeth. When each tooth of the signal rotor moves past the CMP sensor (1), an electrical signal is generated. These AC signals, three per camshaft revolution, are sent to the PCM.