Yamaha 2004 YP400, Service Manual, Page: 14 / 417

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GEN
INFO
FEATURES
EAS00897
FI SYSTEM
The fuel pump delivers fuel to the fuel injector via the fuel filter. The pressure regulator maintains
the fuel pressure that is applied to the fuel injector at only 250 kPa (2.5 kg/cm
2
, 35.6 psi). Accord-
ingly, when the energizing signal from the ECU energizes the fuel injector, the fuel passage opens,
causing the fuel to be injected into the intake manifold only during the time the passage remains
open. Therefore, the longer the length of time the fuel injector is energized (injection duration), the
greater the volume of fuel that is supplied. Conversely, the shorter the length of time the fuel injector
is energized (injection duration), the lesser the volume of fuel that is supplied.
The injection duration and the injection timing are controlled by the ECU. Signals that are input from
the throttle position sensor, crankshaft position sensor, intake air pressure sensor, intake tempera-
ture sensor and coolant temperature sensor enable the ECU to determine the injection duration.
The injection timing is determined through the signals from the crankshaft position sensor. As a
result, the volume of fuel that is required by the engine can be supplied at all times in accordance
with the driving conditions.
1
Fuel pump
2
Fuel injector
3
Ignition coil
4
ECU
5
Catalytic converter
6
Coolant temperature
sensor
7
Crankshaft position
sensor
8
Intake air pressure
sensor
9
Throttle body
0
Intake air temperature
sensor
A
Air filter case
B
Throttle position sen-
sor
C
ISC (idle speed con-
trol) valve
È
Fuel system
É
Air system
Ê
Control system
1
2
3
C
B
5
6
7
8
9
0
A
4
È
É
Ê
Illustration is for reference only.