Features; Outline Of The Fi System - Yamaha XT660Z 2008 Service Manual

EAS00019

FEATURES

EAS00896

OUTLINE OF THE FI SYSTEM

The main function of a fuel supply system is to provide fuel to the combustion chamber at the opti-
mum air-fuel ratio in accordance with the engine operating conditions and the atmospheric temper-
ature. In a conventional carburetor system, the air-fuel ratio of the mixture that is supplied to the com-
bustion chamber is created by the volume of the intake air and the fuel that is metered by the jet used
in the respective chamber. Despite the same volume of intake air, the fuel volume requirement varies
with the engine operating conditions, such as acceleration, deceleration, or operation under a heavy
load. Carburetors that meter the fuel through the use of jets have been provided with various auxil-
iary devices, so that an optimum air-fuel ratio can be achieved to accommodate the constant changes
in the operating conditions of the engine. As the requirements for engines to deliver more perform-
ance and cleaner exhaust gases increase, it becomes necessary to control the air-fuel ratio in a more
precise and finely tuned manner. To accommodate this need, this model has adopted an electroni-
cally controlled fuel injection (FI) system in place of a conventional carburetor system. This system
can achieve an optimum air-fuel ratio required by the engine at all times by using a microprocessor
that regulates the fuel injection volume according to the engine operating conditions detected by var-
ious sensors. Adoption of the FI system has resulted in a highly precise fuel supply, improved engine
response, better fuel economy, and reduced exhaust emissions. Furthermore, the air induction sys-
tem (AI system) has been placed under computer control together with the FI system in order to re-
alize cleaner exhaust gases.
1. Fuel tank
2. Engine trouble warning light
3. Ignition coil
4. Spark plug
5. Fuel pump
6. Idling adjustment screw
7. Throttle position sensor
8. Intake air pressure sensor
9. Air filter case
10. ECU
11. Lean angle cut-off switch
12. Catalytic converter
13. Fuel injection system relay
14. Battery
15. Intake air temperature sensor
16. Coolant temperature sensor
17. Fuel injector
18. Crankshaft position sensor
19. O 2 sensor
20. Air induction system solenoid
21. Air cut-off valve
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FEATURES