Yamaha XMAX 125, Service Manual

Page: 12 / 498

FEATURES
1-3
EAS37P1141
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 (2.50 kgf/cm², 36.3 psi). Accordingly,
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. There-
fore, the longer the length of time the fuel injector is energized (injection duration), the greater the vol-
ume 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, coolant temperature sensor, lean angle sensor, crankshaft position sensor, in-
take air pressure sensor, intake air temperature sensor, speed sensor and O
2
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
3
4
13
14
16
17
6
B
5
11
2
7
9
8
10
C
12
15
A
1. Fuel pump
2. Pressure regulator
3. Fuel injector
4. Ignition coil
5. Coolant temperature sensor
6. ECU (engine control unit)
7. ISC (idle speed control) unit
8. Throttle position sensor
9. Lean angle sensor
10. Speed sensor
11. O
2
sensor
12. Catalytic converter
13. Crankshaft position sensor
14. Intake air pressure sensor
15. Throttle body
16. Intake air temperature sensor
17. Air filter case
A. Fuel system
B. Air system
C. Control system