Ignition System Overview
The electronic ignition system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture at the correct time. To provide optimum engine performance, fuel economy, and control of exhaust emissions, the PCM controls the spark advance of the ignition system. The Electronic ignition system has the following advantages over a mechanical distributor system:
• No moving parts
• Less maintenance
• Remote mounting capability
• No mechanical load on the engine
• More coil cool down time between firing events
• Elimination of mechanical timing adjustments
• Increased available ignition coil saturation time
The electronic ignition system does not use the conventional distributor and coil. The ignition system consists of the following components/circuits:
• Eight ignition coils/modules
• Eight ignition control (IC) circuits
• Camshaft position (CMP) sensor
• 1X Camshaft reluctor wheel
• Crankshaft position (CKP) sensor
• 24X crankshaft reluctor wheel
• Related connecting wires
• Powertrain control module (PCM)
Crankshaft Position Sensor and Reluctor Wheel
(1) Crankshaft
(2) Bolt
(3) CKP Sensor
Crankshaft Position Sensor Reluctor Ring
(1) Key
(2) Crankshaft
(3) Crankshaft Position Sensor Reluctor Ring
The crankshaft position (CKP) sensor is located under the front engine cover. The CKP sensor is a dual magneto resistive type sensor. This sensor is not speed dependent. The dual micro switches monitor both notches of the reluctor wheel for more accuracy. The CKP sensor works in-conjunction with a 24X reluctor wheel. The reluctor wheel is mounted on the rear of the crankshaft. The 24X reluctor wheel uses two different width notches that are 15 degrees apart. This Pulse Width Encoded pattern allows cylinder position identification within 90 degrees of crankshaft rotation. In some cases, cylinder identification can be located in 45 degrees of crankshaft rotation. This reluctor wheel also has dual track notches that are 180 degrees out of phase. The dual track design allows for quicker starts and accuracy.
The PCM also receives a 4X signal from the crankshaft position sensor. The PCM utilizes the 4X signal for the following:
• Tachometer output
• Spark control
• Fuel control
• Certain diagnostics
The CKP signal must be available for the engine to start. The CMP signal is not needed to start and operate the engine. The PCM can determine when a particular cylinder is on either a firing or exhaust stroke by the 24X signal. The CMP sensor is to determine what stroke the engine is on. The system will attempt synchronized and look for an increase in the MAF signal. An increase in the MAF signal indicates the engine has started. If the PCM does not detect an increase in the MAF signal, a re-sync will occur to the opposite cam position. A slightly longer cranking time may be a symptom of this condition.
Camshaft Position Sensor
(1) Bolt
(2) Camshaft Position Sensor
(3) Lower Intake Manifold
The Camshaft Position (CMP) sensor is mounted through the top of the engine block at the rear of the valley cover. The CMP sensor works in-conjunction with a 1X reluctor wheel. The reluctor wheel is located under the cap of the camshaft. The CMP sensor is used to determine whether a cylinder is on the firing or the exhaust stroke. As the camshaft rotates, the reluctor wheel interrupts a magnetic field produced by a magnet within the sensor. The CMP sensor internal circuitry detects this and produces a signal which is used by the PCM. The PCM uses this signal in combination with the CKP 24X signal to determine crankshaft position and stroke.
The CKP signal must be available for the engine to start. The CMP signal is not needed to start and operate the engine. The PCM can determine when a particular cylinder is on either a firing or exhaust stroke by the 24X signal. The CMP sensor is to determine what stroke the engine is on. The system will attempt synchronized and look for an increase in the MAF signal. An increase in the MAF signal indicates the engine has started. If the PCM does not detect an increase in the MAF signal, a re-sync will occur to the opposite cam position. A slightly longer cranking time may be a symptom of this condition.
Powertrain Control Module Description
I added this just because. Hmmmmmm 411?
The powertrain control module (PCM) is designed to maintain exhaust emission levels while maintaining excellent driveability and fuel efficiency. The PCM controls the following operations:
• Fuel control
• Ignition control (IC)
• Knock sensor (KS) system
• Automatic transmission shift functions
• Evaporative emission (EVAP) urge
• Exhaust gas recirculation (EGR)
(1) Connector C1 (Red) opposite the manufacturer's logo
(2) Connector C2 (Blue) same side as the manufacturer's logo
The powertrain control module (PCM) is located in the engine compartment.
The PCM constantly looks at the information from various sensors, and controls the systems that affect vehicle performance. The PCM also performs the diagnostic function of the system. It can recognize operational problems. The PCM also alerts the driver through the malfunction indicator lamp (MIL). When the PCM detects a malfunction, it stores a diagnostic trouble code (DTC). A DTC stored, will identify the problem areas. This will aid the technician in making repairs.
The PCM supplies either 5.0 or 12.0 volts to power various sensors or switches. This is done through resistances in the PCM. The resistance is so high in value that a test lamp will not illuminate when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading because its resistance is too low. Therefore, a DMM with at least 10 megaohms input impedance is required to ensure accurate voltage readings.
The PCM controls output circuits such as the injectors, cooling fan relays, etc. by controlling the ground or the power feed circuit through transistors or a device called an output driver module.