Omni's and Horizon's are equipped with the Electronic Fuel Control system. This consists of a spark control computer, various engine sensors, and a specially calibrated carburetor with an electronically controlled fuel metering system. On fuel injected engines, the computer controls the total amount of fuel injected by slightly modifying the pulses that operate the injectors. The function of this system is to provide a way for the engine to burn a correct air-fuel mixture.
The spark control computer is the heart of the entire system. It has the capability of igniting the fuel mixture according to different models of engine operation by delivering an infinite number of different variable advance curves. The computer consists of one electronic printed circuit board, which simultaneously received signals from all the sensors and within milliseconds, analyzes them to determine how the engine is operating and then advances or retards the timing.
For 1988, this system has been renamed the Single Module Engine Controller (SMEC) system. It functions similarly to the Electronic Fuel Control system, using coolant temperature, engine rpm, and available manifold vacuum for inputs. On turbo engines, it synchronizes the injection pulses with the ignition pulses by reading signals from the Hall Effect pickup in the distributor. Both systems use the oxygen sensor to fine-tune the mixture to actual operating conditions.