Subaru 2002 Impreza Service Manual page 80

CONTROL SYSTEM
Fuel Injection (Fuel System)
C: FUEL INJECTION CONTROL
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The ECM receives signals from various sensors and based on them, it determines the amount
of fuel injected and the fuel injection timing.
It
performs the sequential fuel injection control over
the entire engine operating range except during start-up of the engine.
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The amount of fuel injected depends upon the length of time the injector stays open. The fuel
injection duration is determined according to varying operating condition of the engine. For the
purpose of achieving highly responsive and accurate fuel injection duration control, the ECM per-
forms a new feedback control that incorporates a learning feature as detailed later.
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The sequential fuel injection control is performed such that fuel is injected accurately at the time
when the maximum air intake efficiency can be achieved for each cylinder (i.e., fuel injection is
completed just before the intake valve begins to open).
1. FUEL INJECTION DURATION
Fuel injection duration
i s
basically determined as indicated below:
During engine start-up:
The duration defined below is used.
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Duration of fuel injection during engine start-up .
.
. . . Determined according to the engine cool-
ant temperature detected by the engine coolant temperature sensor.
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During normal operation:
The duration is determined as follows:
Basic duration of fuel injection x Correction factors
+
Voltage correction time
Basic duration of fuel injection
.....
The basic length of time fuel is injected. This is determined
by two factors -the amount of intake air detected by the manifold pressure sensor and the en-
gine speed monitored by the crankshaft position sensor.
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Correction factors
.....
See the next section.
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Voltage correction time ..... This is added to compensate for the time lag before operation of
injector that results from variation in the battery voltage.
FU-30