Efi System Introduction - Sym Joyride 125 Service Manual

5. Fuel Injection System

EFi System Introduction

Based on 4-stroke SOHC engine, displacement 180 c.c. electronically controlled fuel injection.
The O2 sensor enhances the efficiency of the catalytic converter, by dynamically controlling the
Fuel/Air ratio.
Electronic Fuel Injection Device
Fuel supply devices: fuel tank, fuel pump, fuel filter, and fuel pressure regulator.
Fuel control devices: fuel injector, and ECU.
The fuel is pumped from electrical fuel pump in the fuel tank, to the injector on the inlet pipe.
The fuel pressure regulator keeps the pressure around 2.5 Bar. The signals from ECU enable the
injector to spray fuel into the combustion chamber once each two crankshaft-revolutions. The
excessive fuel flows back to the fuel tank through the fuel pressure regulator. Fuel pump is
placed inside the fuel tank to reduce the working noise, and the complicity of fuel pipes.
Electrically controlled ignition and injection system effectively reduce fuel consumption rate and
pollution.
In traditional gasoline engine, carburetor supplies the fuel. The process is done by the engine
vacuum, and the negative pressure in the carburetor mixes fuel with air. Under this condition,
three major processes are done simultaneously in the carburetor: 1. air quantity measurement,
the determination of fuel quantity, the mix of fuel and air.
Electronic fuel injection system separates the three major processes into three different devices:
1. T-MAP sensor measures the air quantity and temperature and sends the signal to ECU as a
reference. 2. ECU determines the amount of fuel to be injected, according to the default A/F rate.
3. ECU enables the injector to spray appropriate fuel amount. The independence of these three
functions will raise the accuracy of the whole process.
EFi engine uses computer-programmed fuel injection, the main features are:
1. The quantity of fuel injected is determined according to the condition of the engine. The engine
RPM, and throttle position determines the fuel quantity and injection time-length.
2. The quantity of fuel injection, and the determination of injection time length, are all controlled
by 16-bit microcomputer.
3. The fuel pressure regulator maintains a 2.5 Bar pressure difference between inlet pipe and fuel
pipe, raising the accuracy of fuel injection.
4. By measuring the air pressure of inlet pipe, this system gives the vehicle better
accommodation to the environment.
5. Air by-pass system supplies fuel and air to stabilize the idle running, and cold starting.
5-2
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