This paper describes a microprocessor engine controller designed for onboard control of closed-loop fuel injection, spark advance, and exhaust-gas recirculation. Developed through the preproduction prototype stage, the controller utilizes software subroutines to accomplish such operations as multiplication and interpolation. Ignition is controlled by means of time delays from relatively widely spaced crankshaft-position pulses. Emissions, driveability, fuel-economy, and hardware-cost comparisons are made between the microprocessor engine controller and a 1977 production analog electronic-fuel-injection controller with a mechanical-advance-controlled distributor. Directions for future development efforts are also described.