Service Manuals, User Guides, Schematic Diagrams or docs for : . Car Manuals Subaru Impreza 2001-2002.2004-2007 Approved Subaru Impreza 2004 WRX STi 08. MECHANISM AND FUNCTION 12. FUEL INJECTION (FUEL SYSTEM) 02. Air Line
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W1860BE.book Page 3 Tuesday, January 28, 2003 11:01 PM
AIR LINE
FUEL INJECTION (FUEL SYSTEM)
2. Air Line
A: GENERAL
The air filtered by the air cleaner enters the throttle body where it is regulated in the volume by the
throttle valve and then enters the intake manifold. It is then distributed to each cylinder where the
air is mixed with fuel injected by the injector. During idling operation, air flows into the cylinder
through the idle air control solenoid valve, bypassing the throttle valve. This enables controlling the
engine idling speed properly.
B: MANIFOLD ABSOLUTE PRESSURE SENSOR
The manifold absolute pressure sensor is attached to the top of the throttle body, and continuously
sends to the engine control module (ECM) voltage signals that are proportional to intake manifold
absolute pressures. The ECM controls the fuel injection and ignition timing based on the intake
manifold absolute pressure signals in addition to other signals from many sensors and other control
modules.
(1) (2)
(A)
(3) (B)
FU-00343
(1) Connector (A) Output voltage
(2) Terminal (B) Absolute pressure
(3) O-ring
FU(H4DOTC)-3
W1860BE.book Page 4 Tuesday, January 28, 2003 11:01 PM
AIR LINE
FUEL INJECTION (FUEL SYSTEM)
C: THROTTLE BODY
In response to operation of the accelerator pedal, the throttle valve in the throttle body opens/clos-
es to regulate the volume of the air drawn into the combustion chamber.
During idling the throttle valve is almost fully closed and the volume of air passing the throttle
valve becomes less than the amount of air that pass through the idle air control solenoid valve.
More than half of the air necessary for idling is supplied to the intake manifold via the idle air con-
trol solenoid valve which controls properly the engine idling speed, so the idling speed needs not
be adjusted.
D: THROTTLE POSITION SENSOR
The throttle position sensor is mounted in the throttle body and linked to the throttle valve.
The throttle position sensor sends the ECM voltage signal corresponding to the opening of the
throttle valve. When the sensor's output voltage exceeds a predetermined level, the ECM interprets
it as complete closure of the throttle valve. When the output voltage is at another predetermined
level, the ECM recognizes that the throttle valve is at a wide open position. Since the output char-
acteristics of the sensor change over years, the ECM is provided with a learning function to be able
to interpret signals into throttle valve angles always correctly.
(3)
(1)
(4)
(2)
(5)
FU-00344
(1) Connector (4) Return spring
(2) Terminal (5) Terminal
(3) Wave washer
FU(H4DOTC)-4
W1860BE.book Page 5 Tuesday, January 28, 2003 11:01 PM
AIR LINE
FUEL INJECTION (FUEL SYSTEM)
E: IDLE AIR CONTROL SOLENOID VALVE
The idle air control solenoid valve is located in the throttle body and regulates the amount of in-
take air that flows bypassing the throttle valve into the intake manifold during engine idling. It is ac-
tivated by a signal from the ECM in order to maintain the engine idling speed at a target speed.
The idle air control solenoid valve is a solenoid-actuated rotary valve consisting of a coil, rotary
valve, spring and housing. The housing is an integral part of the throttle body and provided with a
bypass air port whose opening area is changed by the rotary valve.
(4)
(1)
(1)
(2)
(3)
FU-00345
(1) Connector (3) Inlet port
(2) Outlet port (4) Terminal
FU(H4DOTC)-5
W1860BE.book Page 6 Tuesday, January 28, 2003 11:01 PM
AIR LINE
FUEL INJECTION (FUEL SYSTEM)
F: MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR
The mass air flow and the intake air temperature sensors are integrated into a single unit. The unit
is mounted on the air cleaner case and measures the amount as well as the temperature of the in-
take air.
The measured amount and temperature are converted into electrical signals and sent to the ECM.
The ECM uses these signals to control injection and ignition timing as well as the fuel injection
amount.
(1)
(2)
(3)
(A)
FU-00346
(1) Mass air flow and intake air temperature sensor (A) Air
(2) Mass air flow sensor
(3) Intake air temperature sensor
G: TUMBLE GENERATOR VALVE
A tumble generator valve is provided on each engine bank, between the intake manifold and in-
take air ports. The right bank tumble generator valve has butterfly valves for the #1 and #3 cylinders
and the left bank tumble generator valve has those for the #2 and #4 cylinders. The two butterfly
valves in each tumble generator valve are fitted on a single shaft that is driven by an actuator.
The tumble generator valves are controlled by the ECM according to the coolant temperature and
the time elapsed after start of the engine. When the engine is started, the butterfly valves are moved
to the closing ends. In this state, the intake air flows at very high speeds passing through narrowed
passages in the directions determined by the individual intake air ports in the cylinder head. This
creates tumbling air motions in the cylinders, which enables lean mixtures to be ignited and thus
harmful exhaust emissions to be reduced during engine start. The tumble generator valves are fully
open when the engine is operating at an ordinary driving speed, allowing intake air to flow without
being changed in direction and velocity.
FU(H4DOTC)-6
W1860BE.book Page 7 Tuesday, January 28, 2003 11:01 PM
AIR LINE
FUEL INJECTION (FUEL SYSTEM)
(3)
(1)
(2)
(A) (4) (B) (4)
(5) (6) (5) (6)
(3) (3)
(9) (9)
(7) (7)
(8) (8)
(10) (10)
FU-00998
(A) Activated
(B) Not activated
(1) Actuator (6) Tumble generating air passage
(2) Tumble generator valve position sensor (7) Intake main air passage
(3) Tumble generator housing (8) Piston
(4) Intake manifold (9) Injector
(5) Tumble generator valve (10) Cylinder Head
FU(H4DOTC)-7
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