Ignition System: Description and Operation

Purpose
The Ignition System is designed to ignite the compressed air/fuel mixture supplied to the engine by the fuel and air systems. The ignition system also provides engine timing information to the Powertrain Control Module (PCM) for proper vehicle operation.

This vehicle uses Coil-Per-Plug, which has one coil for each of the eight cylinders, and also uses a Camshaft Position Sensor (CMP) for the identification of number one cylinder.

Electronic Ignition Components

The Electronic Ignition (EI) system for this engine consists of the following components:

^ crankshaft position sensor (CKP)
^ camshaft position sensor (CMP)
^ Coil-Per-Plug units
^ the spark control portion of powertrain control module (PCM)
^ related wiring

Operation
The Coil-Per-Plug works in the same manner as a standard coil pack. The Coil-Per-Plug systems fire only one spark plug at a time instead of two like the standard coil packs. Since there is one coil on each spark plug, the coils will fire the spark plugs on the compression stroke only. The PCM uses information from the CMP to identify the position of cylinder one in order to synchronize the firing of the coils.
The CKP is used to indicate crankshaft position and engine speed information to the PCM. By sensing a missing tooth on a trigger wheel mounted on the crankshaft damper, the CKP is also able to identify a specific point in the travel of piston number one. The PCM uses the information from the CKP to generate an internal Profile Ignition Pickup (PIP) signal that is sent to the PCM.

Failure Mode Effects Management

During some electronic ignition system concerns, the failure mode effects management portion of the PCM will maintain vehicle operation:

^ If the spark output signal is interrupted, the powertrain control module will automatically turn the Coil-Per-Plug unit ON and OFF using the CKP signal input. This will result in fixed-spark timing (10 degrees BTDC) and fixed dwell time (no CCD).

^ If the powertrain control module does not receive the CMP input during engine cranking, random ignition coil synchronization will be attempted from the powertrain control module. Therefore, several start attempts (cycling ignition switch from OFF to START) may be required to start the engine.

^ If the powertrain control module loses CMP input while the engine is running, the powertrain control module will retain the proper firing sequence and it will continue to fire the Coil-Per-Plug units to maintain engine operation.