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Engine Control Sequence
NOTICE: The ignition switch is wired directly to both channels of the ACU. When the ignition
switch is set to the ON position (open circuit) the ACU is enabled to supply fuel and
spark to the engine. This switch is the primary means of turning the engine OFF.
If the EECS has power:
1. The Ignition switch is identified in the ON position.
2. The system identifies the engine rotation.
3. As a result, the system supplies fuel and spark to operate the engine. In some cases, this function
can be disabled by the following:
• Fuel flow manually turned off or not available
• Cylinder disabled for overspeed
• Cylinder disabled for overboost
• Cylinder disabled for dead-cylinder detection.
Engine Synchronization
"Engine synchronization" refers to the speed and position of the engine crankshaft. The EECS uses
the crankshaft and camshaft speed sensors to calculate engine speed and position. Although the
engine can operate with full functionality with either sensor, position data from the camshaft sensor
is necessary for full sequential fuel injection.
Fuel Control
The fuel system supplies a mixture of fuel and air to the cylinders under all conditions of operation.
The fuel system will keep the correct fuel pressure during all conditions of normal operation.
The EECS electronically activates fuel injection and adjusts fuel for each cylinder to control the
air/fuel ratio by engine speed and engine load.
Ignition Control
The EECS controls ignition events electronically. The EECS calculates ignition timing based on
engine speed and engine load.
When only one spark plug is operational on a particular cylinder, the EECS adjusts the spark timing
on the remaining spark plug of that particular cylinder to keep power loss to a minimum.
Load Sensing
The EECS calculates airflow by the following redundant methods:
• Venturi-delta-pressure
• Speed density
• Speed throttle.
The EECS compares the different sources of engine airflow to identify sensor failures.
Theory of Operation
Page 16
TEO-540-A1A Engine Installation and Operation Manual
© 2018 Avco Corporation. All Rights Reserved
October 2018
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