Electronic Fuel Injection

The Electronic Control Unit/Assembly (ECU/ECA), through various input sensors, monitors battery voltage, engine RPM, intake air volume, cranking signal, crankshaft angle, intake air temperature, radiator and engine coolant temperatures, exhaust oxygen content, throttle position, atmospheric pressure, gearshift lever position, clutch engagement, braking, power steering operation, and A/C compressor operation.

ECU/ECA uses this input information in controlling fuel injection and operation of other output devices. On Miata, MX-3, MX-6 turbo, Protege, 323, 626 turbo and 929, spark timing is controlled by ECU.

ECU/ECA has a built-in fail-safe mechanism. If a fault occurs while driving, ECU/ECA will substitute pre-programmed values. Driving performance will be affected, but vehicle may still be driven.

ECU/ECA has a self-diagnostic function, which allows unit to store a number of trouble codes in its memory. A Malfunction Indicator Light (MIL) informs the driver of system problems. MIL is in center of instrument cluster, under engine symbol marked CHECK.