E023 Part 2 of 2

Diagnostic Chart.:

Wiring Diagram.:

DESCRIPTION:

The EST distributor produces one 5 volt Distributor Reference Pulse each time that a cylinder reaches 10° BTDC (base timing). The reference pulses are sent from the distributor to the PCM/ECM on circuit 430 (the distributor reference signal). The PCM/ECM adds spark timing information to the reference pulses received from the HEI and sends out 5 volt Electronic Spark Timing pulses (EST) on circuit 423. The PCM/ECM can choose to control spark timing. The HEI bypass circuit 424 is turned on by the PCM/ECM (approximately 5 volts) when the PCM/ECM wishes to control timing. When the PCM/ECM wants the HEI module to control timing, the HEI bypass circuit is turned off and the HEI module grounds circuit 423 (EST). The PCM/ECM sends EST pulses to the HEI; the HEI module shorts the EST pulses to ground when the bypass signal from the PCM/ECM to the module is low (less than .5 volts).


CIRCUIT DESCRIPTION:

Possible causes of code E23 are:

1. Reference pulses are being received by the PCM/ECM and the bypass line is low, but the PCM/ECM detects pulses on the EST line. This could be caused by the bypass line shorted to voltage at the distributor.

2. Reference pulses are being received by the PCM/ECM and the bypass line is high, and the PCM/ECM does not detect a signal on the EST line. This could be caused by an open or shorted to ground on the EST line or the bypass line open or a shorted to ground.