3-32 ENGINE CONTROL SYSTEM
SYSTEM OPERATION
This system is operated by the vacuum created during engine
operation and controlled by the ECM.
To operate the system (open/close the shut off valve to change
the intake tract), the collector, check valve, vacuum tank, VSV
and depression chamber are connected with hoses as shown in
the illustration.
A rod is used to connect the shut off valve and depression
chamber for opening and closing the valve.
• LOW & MID SPEED RANGE
When engine speed is below the preset value (*), the ECM gen-
erates a signal to turn the VSV ON, applying vacuum to the
depression chamber which closes the shut off valve.
With the valve closed during the engines low to mid speed
range, intake air is supplied through the low/mid speed intake
tract only.
In this operating mode, intake air speed is boosted and, com-
bined with the resonance effect, increases low and mid speed
range engine torque.
*: Preset value;
DF225: approx. 4 200 r/min DF250: approx. 4 800 r/min
• HIGH SPEED RANGE
When the engine speed is above the preset value (*), the ECM
generates a signal to turn the VSV OFF, and vacuum is no
longer applied to the depression chamber.
Without vacuum the shut off valve return spring returns and
holds the valve in its normal open position.
In this operating mode, intake air is supplied to the engine
through the high speed intake tract only.
This enlarges the intake tract volume, improves intake inertia
and efficiency, which increases the engines output power.
LOW & MID SPEED
Shut off valve closed
HIGH SPEED
Shut off valve opened
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