Skylark L4-138 2.3L SOHC VIN 3 MFI QUAD 4 (1992)
Ignition Control Module: Description and Operation
Distributor Reference Signal
This system uses similar circuits between the ICM and the ECM that distributor type systems use. Following is a brief description for each of the IC
circuits.
^ 7X Reference - CKT 483 - The CKP sensor generates a signal to the ICM which results in a reference pulse (square wave signal) being sent to the
ECM. The ECM 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 shorted.
^ Reference ground - CKT 453 - This wire is grounded through the module and insures that the ground circuit has no voltage drop between the ICM
and the ECM which could affect performance.
^ Ignition Control 1 & 2 - CKT's 423 & 485 - The ECM sends the Ignition Control (IC) pulses to the ICM on these circuits, and also monitors these
pulses. These signals are similar to the 7X reference pulse square wave except that the ECM uses sensor inputs to determine the pulse timing to
control spark advance.
When the ECM receives the 7X signal, it will determine which pair of cylinders will be fired (1 & 4 or 2 & 3). It will tell the ICM which cylinder
pair will be fired via CKTs 423 or 485.