OBD II - Electronic Ignition System (EI High Data Rate)

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

CONSTRUCTION
The EI High Data Rate systems consist of an Ignition Control Module (ICM), a Crankshaft Position Sensor (CKP), a PCM, and connecting wiring harnesses. Six cylinder applications use a six tower coil pack and eight cylinder applications use two four tower coil packs.

OPERATION
This system uses an Electronic Ignition (EI) system with a stand-alone ICM. The EI High Data Rate system eliminates the need for a distributor by using multiple coil packs. Each coil within the pack fires two spark plugs at the same time. The plugs are paired so that as one fires during the compression stroke, the other fires during the exhaust stroke. The next time the coil is fired, the plug that was on exhaust will be on compression and the plug that was on compression will be on exhaust.

The CKP is used to indicate crankshaft position and speed information to the ICM. 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 1. The ICM uses this information from the CKP to generate a Profile Ignition Pickup (PIP) signal that is sent to the PCM.

Once the PCM recognizes the PIP signal, fuel and spark functions are enabled. The calculated spark target is sent from the PCM to the ICM as a pulse width modulated digital signal called the Spark Output (SPOUT). The ICM decodes the SPOUT signal and fires the next spark at the commanded spark target.

Coil firing is initiated by energizing the ICM coils in sequence using the missing tooth as a reference and firing at the commanded spark target.

By energizing the primary side of the coils on proper sequence and connecting the secondary wires in accordance with the engine firing order, a power stroke is achieved on each cylinder. In addition, an Ignition Diagnostic Monitor (IDM) signal is transmitted on each spark firing. This signal communicates information by pulse width modulation and provides a clean, buffered signal with a frequency proportional to engine speed for tachometer operation.

The ICM also serves as an electric switch for a coil primary circuit. When the switch closes, current flows and a magnetic field expands around the primary coil. When the switch opens, the field collapses and causes the secondary coil to fire the spark plugs at high voltage.