Electronic Fuel Injection Control Unit

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.

The ECU/ECA uses this input information in controlling fuel injection and the actuating of other output devices. On Miata, MX-6 turbo, 626 turbo and all 929 models, spark timing is controlled by the ECU.

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

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