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Basic functions of engine control system
Basic functions of the engine control system include fuel injection control, idle speed control and ignition timing control
that are synthetically controlled by ECM which has a built–in microcomputer.
Outline of engine control functions Electronic fuel injection
The electronic fuel injection control system controls injection timing and injection time (amount of injection). As ECM has
an operation expression for injection time stored in its memory, it calculates the optimum injection time according to the
input signals (amount of intake air, engine speed, cooling water temperature, etc.) from sensors.
Idle speed control (ISC)
ECM has target idle speeds for various engine conditions stored in its memory. When it receives signals (including cool-
ing water temperature, D–range signal of A/T vehicles, etc.) from each sensor, it controls so that the idle speed becomes
the target speed.
Electronic spark advance (ESA) control
ECM has optimum ignition timing for various engine conditions stored in its memory. When it receives signals (including
engine speed, amount of intake air, cooling water temperature and throttle opening) from each sensor, it controls the
ignition timing based on such signals.
Self diagnosis function
The self–diagnosis function is used to diagnose a trouble. When an abnormal signal is fed to ECM, it detects the
abnormality, stores that data in its backup RAM and indicates what the trouble is by using code numbers and diagnosis
lamp when probed.
Fail–safe function
When an abnormal signal is fed to ECM, the fail–safe function selects the standard value stored in its ROM of ECM to
avoid the engine failure. When a critical abnormality has occurred, however, it makes the engine stop.
Back–up (failsafe) function
The back–up failsafe function executes a certain fuel injection and ignition control when an abnormality has occurred in
the microcomputer in ECM so that driving can be continued long enough to return to the repair facility.
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