Ignition System: Description and Operation

Description
This system uses similar circuits between the ICM and the PCM that a distributor type system uses. Following is a brief description of the IC circuit. The PCM sends the Ignition Control (IC) pulses to the ICM on the ignition control A & B. The signals are similar to the 7x reference pules square wave except that the PCM uses the sensors inputs to determine the pules timing to control spark advance. When the PCM receives the 7x reference signal, the PCM determines which pair of cylinders to fire 1 and 4 or 2 and 3.


Operation
Crankshaft Position (CKP) Sensor Activity (7X reference) - The CKP sensor generates a signal to the ICM which results in a reference pulse (square wave signal) being sent to the PCM. The PCM uses this signal to calculate crankshaft position, engine speed and injector pulse width. The engine will not start or run if this circuit is open or grounded.

Reference Low - This wire is grounded through the ICM and insures that the ground circuit has no voltage drop between the ICM and the PCM which could affect performance. The PCM compares voltage pulses on the 7X or reference input to those on this circuit, ignoring any pulses that appear on both. A pulse that appears on the reference low circuit alone is assumed to be caused by Radio Frequency Interference (RFI).

Ignition Control (IC) 1 & 2 - The PCM sends the ignition control pulse to the ICM on these circuits. These signals are similar to the 7X reference pulse square wave except that the PCM uses sensor inputs to determine the pulse timing to control spark advance. When the PCM receives the 7X signal, it will determine which pair of cylinders will be fired (1 & 4 or 2 & 3). It then tells the ICM which cylinder to fire through the ignition control circuits.