Distributor Operation

Distributor Assembly:

The distributor assembly is mounted directly to the camshaft assembly next to the water pump assembly. It directs the spark from the ignition coil assembly to the proper spark plug secondary wire through a rotor. The secondary output connectors in the distributor cap are each connected to an individual spark plug. The connectors in the cap are arranged for convenience in routing spark plug wire harness assemblies. The corresponding cylinder number is molded into the distributor cap next to each output connector.

The distributor assembly also contains a signal disk and two optical camshaft position (CMP) sensor assemblies that provide signals to the ECM for timing control. One CMP sensor assembly senses 360 equally-spaced slots in the signal disk to provide 720 signals per camshaft revolution for high-resolution timing control. The other CMP sensor assembly senses eight disk slots of variable length, providing a low-resolution signal that tells the ECM which spark plug is being fired. Power for the optical CMP sensor assemblies, a system ground, and the two CMP sensor assembly signals are transferred between the ECM and the distributor assembly through a shielded harness connected to the four-terminal connector on the distributor.

The ignition system supplies two timing inputs to the ECM, a high resolution signal (360 pulses per one camshaft revolution) and a low resolution signal (eight pulses per one camshaft revolution). The ECM can determine if one of the timing inputs is not being received by comparing the two inputs. If the ECM detects one timing pulse without detecting the other timing pulse, diagnostic trouble code 16 will set.

The reference signals toggle between 0 and 5 volts as the camshaft assembly turns. Therefore, an open, a short to voltage, a short to ground, or a defective sensor inside the distributor assembly can prevent the voltage from pulsing at the ECM.