Subaru 2002 Impreza Service Manual page 47

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CONTROL SYSTEM
Fuel lniection (Fuel Svstem)
Crankshaft position sensor
b
Camshaft position sensor
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Engine coolant temperature sensor
*
Atmospheric pressure sensor
e
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D: IGNITION SYSTEM CONTROL
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The ECM determines operating condition of the engine based on signals from the pressure sen-
sor, engine coolant temperature sensor, intake air temperature sensor, crankshaft position sensor
and other sources. It then selects the ignition timing most appropriate for the condition thus deter-
mined from those stored in its memory and outputs at that timing a primary current OFF signal to
the ignitor to initiate ignition.
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This control uses a quick-to-response learning feature by which the data stored in the ECM
memory is processed in comparison with information from various sensors and switches.
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Thus, the ECM can always perform optimum ignition timing taking into account the output, fuel
consumption, exhaust gas, and other factors for every engine operating condition.
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Ignition control during start-up
Engine speed fluctuates during start of the engine, so the ECM cannot control the ignition timing.
During that period, the ignition timing is fixed at 10" BTDC by using the IO" signal from the crank-
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Knock sensor b
Throttle position sensor
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Intake air temperature and
pressure sensor
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ECM
Neutral position switch (MT)
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ParWNeutral position switch
(AT)
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NC switch
1
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Ignition coil and
ignitor assembly
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NF0031
FU-31