Ignition Circuits

IGNITION CIRCUITS
The ignition system uses many of the the same ignition module-to-PCM circuits as did previous Delco engine management systems using distributor type ignition. The following describes the PCM to ignition control module circuits:

3X reference PCM input (CKT 430)
From the electronic ignition module, the PCM uses this signal to calculate engine speed and crankshaft position. The PCM compares pulses on this circuit to reference low CKT 453. The PCM also uses the pulses on this circuit to initiate fuel injector pulses. If the PCM receives no pulses on this circuit, no fuel injection pulses will occur and the engine will not run.

Reference low PCM input
This is a ground circuit for the digital RPM counter inside the PCM, but the wire is connected to engine ground only through the ignition control module. Although this circuit is electrically connected to the PCM, it is not connected to ground at the PCM. The PCM compares voltage pulses on the 18X and 3X reference input circuits to any on this circuit, ignoring pulses that appear on both. If the circuit is open, or connected to ground at the PCM, it may cause poor engine performance and possibly a Malfunction Indicator Lamp (MIL) with no DTC set.

(CAM) Camshaft Signal (CKT 630)
The PCM uses this signal to determine the position of the # 1 piston during its power stroke, allowing the PCM to calculate true Sequential Multi-port Fuel Injection (SFI). A loss of this signal will set a DTC P0341. If the CAM signal is lost while the engine is running, the fuel injection system will shift to a calculated sequential fuel injection based on the last fuel injection pulse and the engine will continue to run. The engine can be restarted and will run in the calculated sequential mode as long as the fault is present with a 1 in 6 chance of being correct. Refer to DTC P0341 Camshaft Position (CMP) Sensor Circuit Performance.