Electronic Ignition System

The Electronic Ignition (EI) system produces and controls a high-energy secondary spark. This spark is used to ignite the compressed air/fuel mixture at precisely the correct time. This provides optimal performance, fuel economy, and control of exhaust emissions. This ignition system uses an individual coil for each cylinder. The ignition coils and the driver modules are contained within 2 assemblies, one for each cylinder bank. The assemblies are mounted in the center of each camshaft cover with short boots connecting coils to the spark plugs. The driver modules within each ignition coil are commanded ON/OFF by the ECM. The ECM primarily uses engine speed and position information from the Crankshaft Position (CKP) sensor and the Camshaft Position (CMP) sensor. This controls the sequence, dwell, and timing of the spark. The EI system consists of the components listed below.

• Camshaft Position Sensor
  
  The Camshaft Position (CMP) sensor signal is a digital ON/OFF pulse, output once per revolution of the camshaft. The CMP sensor does not directly affect the operation of the ignition system. The CMP sensor information is used by the ECM to determine the position of the valve train relative to the crankshaft. By monitoring the CMP and CKP sensor signals, the ECM can accurately time the operation of the fuel injectors. The ECM supplies the CMP sensor with a 12-volt reference circuit and a low reference circuit. The CMP sensor signal is an input to the ECM. The CMP sensor is protected from electromagnetic interference by the same shielding circuit used by the CKP sensor.
• Crankshaft Position Sensor
  
  The Crankshaft Position (CKP) sensor is a permanent magnet generator, known as a variable reluctance sensor. The CKP sensor is mounted in left rear of cylinder block. A crankshaft mounted reluctor wheel that has 60 slots, 2 of which are missing, alters the magnetic field of the sensor. This arrangement results in the CKP sensor output of 58 pulses per crankshaft revolution. The 2 missing slots represent the position of cylinder No. 1 and 4 pistons 84 degrees Before Top Dead Center (BTDC). The CKP sensor is connected to the ECM by a signal circuit and a low reference circuit. Both CKP sensor circuits are protected from electromagnetic interference by a shielding ground circuit. The shielding circuit is grounded through the ECM. Using the CKP signals in conjunction with those from the CMP sensor the ECM determines the engine position with great accuracy.
• Ignition Coils
  
  The ignition system uses a ignition coil assembly for each bank. Each ignition coil assembly consist of 3 ignition coils. The ignition coil assemblies consist of the ignition voltage circuit, ground circuit and Ignition Control (IC) circuit for each ignition coil.

  The ignition coil assemblies are mounted in the center of each camshaft cover with short boots connecting the coils to the spark plugs. The ECM primarily uses engine speed and position information from the CKP sensor and the CMP sensor to control the sequence, dwell, and timing of the spark. The ECM can command each ignition coil ON/OFF by grounding the IC circuit of the ignition coil. The IC circuits are Pulse-Width Modulated (PWM) in order to precisely control the spark events.

• Engine Control Module
  
  The ECM controls all ignition system functions and constantly corrects the spark timing. The ECM monitors information from various sensor inputs that include the following components:
  • TP sensor.
  • ECT sensor.
  • MAF sensor.
  • IAT sensor.
  • VSS.
  • Knock sensor.
  • Transmission gear position or range information sensors.
• Modes Of Operation
  
  There is one normal mode of operation, with spark under ECM control. If CKP sensor pulses are lost, engine will not run. The loss of a CMP sensor signal may result in a longer crank time since the ECM cannot determine which stroke the pistons are on. DTCs are available to accurately diagnose the ignition system with a scan tool.