<div class="htmlview paragraph">An electronic engine control system that uses a microcomputer has been developed. It combines four control systems - fuel injection, ignition timing, EGR and idle speed control - utilizing the engine speed and intake air quantity for its main parameters.</div> <div class="htmlview paragraph">The control circuit is composed of an 8-bit microcomputer combining an 8k byte ROM, RAM, a custom designed input/output LSI, and two hybrid integrated circuits, one has voltage regulators and another has input/output interface circuits.</div> <div class="htmlview paragraph">The control program consists of a main program, a fail-safe program for noise protection and a check program for diagnostic functions.</div> <div class="htmlview paragraph">The main program uses interrupt techniques to control effectively the four items by one microcomputer. The interrupt requests occur from crankshaft position signal and interval timer signals.</div>