Subaru 2002 Impreza Service Manual page 62

FUEL LINE
Fuel injection (Fuel System)
E: FUEL PUMP AND FUEL LEVEL SENSOR ASSEMBLY
1. FUEL PUMP
The fuel pump consists of a motor, impeller, pump casing, pump cover, check valve and filter. It
is located in the fuel tank and combined with the fuel level sensor into a single unit. The operation
of this impeller type pump is very quiet.
Fuel pump
Fuel level sensor
Jet pump
Mesh filter
Fuel temperature sensor
Impeller
Check valve
Pump casing
NF0474
(9) Motor armature
(IO) Suction
(1 1 ) Discharge
(1 2) Vane groove
A: From engine (return line)
B: From sub tank
C: To engine (delivery line)
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When the ignition switch is turned ON, fuel pump relay is activated. Then the motor operates
to rotate the impeller.
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As the impeller rotates, fuel in a vane groove of the impeller flows along the fuel passage into
the next vane groove by centrifugal force. When fuel flows from one groove to the next, a pressure
difference occurs due to friction. This creates a pumping effect.
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The fuel pushed up by rotation of the impeller then passes through the clearance between the
armature and the magnet of the motor and is discharged through the check valve.
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When the fuel discharge pressure reaches the specified level, the relief valve opens and excess
fuel is released into the fuel tank. In this manner, the relief valve prevents an abnormal increase
in fuel pressure.
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When the engine and the fuel pump stop, spring force acts on the check valve to close the dis-
charge port, so that the fuel pressure in the fuel delivery line is retained.
FU-12