Component Systems

Ignition and Timing Systems
The ignition system provides spark control to the engine during all modes of operation. The ignition system consists of three subsystems: primary ignition, secondary ignition, and timing advance.

Primary Ignition Components
The primary ignition components include the coil primary circuit, the power transistor, and the ignition switch. When the ignition switch is turned on, it charges the primary coil windings. When the engine is running, the Powertrain Control Module (PCM) sends a signal to the power transistor. The power transistor grounds the negative side of the coil primary circuit, generating the proper voltage in the secondary circuit which induces spark.

Secondary Ignition Components
The secondary ignition components include the spark plugs, the spark plug wires, the distributor cap, the rotor, and the coil secondary circuit. When the power transistor grounds the primary circuit, the inductive charge built up in the secondary circuit sends a spark from the coil to the rotor. The rotor and distributor cap then send a spark to each spark plug.

Timing Advance Components
The spark advance and retard functions are controlled by the Powertrain Control Module (PCM). The PCM receives signals from various switches and sensors and then sends the spark timing signal through the power transistor and the ignition coil.

Camshaft Position Sensor

Camshaft Position (CMP) Sensor:

The Camshaft Position (CMP) sensor (Figure 1) is mounted inside the distributor housing. The CMP sensor has a rotor plate and a wave-forming circuit. The rotor plate has 360 slits for 1 degree signals and 6 slits for 120 degree signals. When the rotor plate passes between the Light Emitting Diodes (LEDs) and the photo diode built into the wave-forming circuit, an input signal is generated and sent to the Powertrain Control Module (PCM). This signal notifies the PCM of the engine speed at 1 degree intervals and the crankshaft position at 120 degree intervals.

Knock Sensor

Knock Sensor (KS):

The Knock Sensor (KS) (Figure 2) detects engine knocking conditions and sends a signal to the Powertrain Control Module (PCM). A knocking vibration from the engine block is applied as a pressure to the piezoelectric element of the KS. This vibrational pressure is then converted into a voltage signal which is delivered to the PCM. The PCM then retards the ignition timing to compensate for the condition. The KS is attached to the engine block between the cylinder banks. The MIL will not be illuminated for a KS fault.

Power Transistor

Power Transistor:

The ignition timing is controlled by the Powertrain Control Module (PCM). The PCM detects information such as the injection pulse width and Camshaft Position Sensor (CMP) signal which varies every moment. Then, responding to this information, an ignition signal is sent to the power transistor 'which is combined with the Camshaft Position Sensor (CMP) as one component (Figure 3). The power transistor amplifies this signal and turns the ignition coil primary circuit on and off, inducing a high voltage in the secondary circuit. The ignition coil is a small, molded type.