The electronic ignition system is of the direct ignition system (DIS) type and is controlled by the powertrain control module (PCM). The electronic ignition system is composed of the following components:
The electronic ignition system provides the following benefits:
The electronic ignition system components cannot be disassembled or repaired. A component that is correctly diagnosed as faulty must be replaced as a complete unit.
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 crankshaft position (CKP) sensor (1) is located in the front cover of the cylinder block near the crankshaft pulley (2). The CKP sensor produces an AC signal that increases in both frequency and amplitude as the engine speed increases. The CKP sensor signal is sent to the PCM in order to indicate the RPM and the crankshaft position. The PCM uses the CKP sensor signal along with the camshaft position (CMP) sensor signal for the following purposes:
The CKP sensor reluctor (2) has 34 teeth and is mounted on the crankshaft behind the timing chain cover and the crankshaft pulley. When the crankshaft (1) rotates, the CKP sensor reluctor teeth pass by the CKP sensor (3) 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 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.
The camshaft position (CMP) sensors are located in the cylinder head cover near the number 4 cylinder. Each CMP sensor is a signal generator. The PCM relies on the information provided by the CMP sensor in order to perform the following:
The 1.8L engine uses two magnetic resistance element (MRE) type CMP sensors. The individual CMP sensors for the intake camshaft and the exhaust camshaft, provide the control module with the information necessary to operate the two CMP actuator systems independently. The intake CMP sensor (1) signal rotor (4) is part of the intake camshaft and has 3 notches located on the outer circumference. When the CMP sensor signal rotor notches rotate past the CMP sensor, the electrical resistance of the sensor's magnetic field changes and the output voltage to the control module changes from High or Low. The exhaust CMP sensor (2) and the exhaust camshaft signal rotor (3) operate the same as the intake CMP sensor and intake camshaft. The MRE design sensors provide a more accurate digital signal for the PCM.
The knock sensor (KS) (2) is located below the intake manifold (1), on the engine block between cylinder 2 and cylinder 3. The KS detects engine detonation and sends a signal to the PCM. The PCM uses the input from the KS to adjust the ignition timing in order to control detonation. For detailed information on the operation of the KS refer to Knock Sensor (KS) System Description.
Consider the following important information when servicing the ignition system:
