General System

System Diagram:

The Mazda 3.0 liter, V-6 cyl. gasoline engine is equipped with a computer controlled electronic fuel injection, ignition and emission control system. The Engine Control Unit (ECU) is the central processor for all engine management functions. The system maintains an air/fuel mixture as close as possible to the ideal stoichiometric ratio, to maintain good driveability and reduce emissions for all operating conditions. The ECU monitors various sensors mounted on the engine, including an exhaust gas oxygen sensor, then uses this information to modify fuel injector duration ("ON" time), regulate ignition timing, and operate certain emission control devices. Fuel is supplied to the injectors at high pressure and the computer energizes the injectors (either all at once or in pairs) for varying lengths of time, depending on the amount of fuel required for any given engine speed and load.

To provide a margin of safety by maintaining driveability in the event of certain system failures, the ECU has a fail-safe mode of preprogrammed values. The output of the ECU will automatically switch to fail-safe mode if a fault is detected in any of these components and/or systems:

^ Airflow meter
^ Atmospheric pressure sensor
^ Feedback system
^ Intake air thermosensor
^ Oxygen sensor
^ Throttle sensor
^ Water thermosensor

The system incorporates self-diagnostic capability monitored via a dash mounted malfunction indicator lamp (MIL). When the system detects a fault in a monitored component and/or circuit, the lamp will light and stay on (while the engine is running), alerting the driver to seek service. The technician can then extract trouble codes from the ECU to aid in the performance of efficient troubleshooting and repair.

Components can be grouped as ECU input and output devices. Input devices control or produce voltage signals monitored by the ECU. Output devices are components controlled by the ECU. Not all of these devices are monitored by the on-board diagnostic system.

INPUT DEVICES
^ A/C switch
^ Airflow meter (code 08)
^ Atmospheric pressure sensor (code 14)
^ Distributor "G1" and "G2" signals (codes 03 and 04)
^ Engine Control Unit (ECU)
^ Feedback system (code 17)
^ Idle switch (in throttle sensor)
^ Ignition pulse (code 01)
^ Ignition switch ("START" position)
^ Inhibitor switch (A/T)
^ Intake air thermosensor
-In airflow meter (code 10)
-In dynamic chamber (code 11)
^ Neutral and clutch switches (M/T)
^ Oxygen sensor (code 15)
^ Power steering pressure switch
^ Stop light switch (M/T)
^ Test connector
^ Throttle sensor (code 12)
^ Water thermosensor (code 09)

OUTPUT DEVICES
^ A/C relay/cut-off
^ Bypass air control (BAC) valve
-Air valve
-Idle speed control (ISC) valve (code 34)
^ Fuel injectors/injection timing
^ Igniter
^ Malfunction indicator lamp (MIL)
^ Oxygen sensor heater
^ Pressure regulator solenoid valve (code 25)
^ Purge control solenoid valve (code 26)
^ Switch monitor function
^ VRIS solenoid valve (code 41) [1]

[1]Variable resonance induction system