Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Electronic Fuel Injection
The PCM, 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.
PCM uses this input information to control fuel injection and operation of other output devices. On Miata, MX-3, MX-6, Protege, 323, 626 and 929, spark timing is controlled by PCM.
PCM has a built-in fail-safe mechanism. If a fault occurs while driving, PCM will substitute pre-programmed values. Driving performance will be affected, but vehicle may still be driven.
PCM 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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.