Electronic Spark Control Module: Description and Operation

The Electronic Spark Advance (ESA) computer with On-Board Diagnostics controls the air-fuel ratio of the carburetor and the ignition timing. The computer receives signals from various sensors and processes them to determine the air-fuel ratio of the carburetor and ignition timing.
The Electronic Spark Advance/Electronic Fuel Control (ESA/EFC) computer is programmed to monitor several different component systems. If a malfunction in a monitored circuit is detected often enough to indicate an actual problem, a corresponding ``fault code'' is stored in the computer. If the malfunction is repaired or ceases to exist, the code will be erased from the computer's memory after 20---40 ignition key on/off cycles.
Fault codes that are stored in the computer must be called up and displayed by using a diagnostic readout tool (tool No. C-4805 or equivalent). The diagnostic readout tool is used to check out one of four different modes: the Diagnostic Test Mode, the Circuit Actuation Test Mode (ATM), the Sensor Test Mode and the Switch Test Mode.