Efi System Introduction - Sym RV 250i Service Manual

4. Fuel Injection System

EFi System Introduction

Based on 4-stroke SOHC engine, displacement 250 c.c. electronically controlled fuel injection, fuel vapor
absorbed by activated carbon canister. The engine burns off the blow-by fuel-gas in the crankcase
through the fuel-air separating device. The O
by dynamically controlling the Fuel/Air ratio.
Electronic Fuel Injection Devices
Consist of fuel supply devices: fuel tank, fuel pump, fuel filter and fuel pressure regulator.
And fuel controll 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 fuel pressure around 294±6kPa. The signals from ECU enable the injector to
spray fuel into the combustion chamber once every two crankshaft revolutions. The excessive fuel flows
back to the fuel tank through the fuel pressure regulator. Fuel pump is placed within the tank to reduce the
working noise, and the complicity of fuel pipes. Electronically controlled ignition and injection system
effectively reduce the fuel consumption rate and pollution.
In the traditional gasoline engine, the carburetor supplies the fuel. The process is done by the engine
vacuum and the negative pressure in the carburetor by mixing fuel and air. Under this condition, three
major processes are done simultaneously in the carburetor: 1. Air quantity measurement. 2. Fuel quantity
determination. 3. Mixing of fuel and air.
Electronic Fuel Injection System distributes the three major processes to three different devices: 1. MAP /
TA 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 decided according the condition of the engine. The engine RPM, and
throttle position determines the fuel quantity and injection time-length. This throttle-controlled fuel
injection is better responding and more accurate.
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 294±6 kPa pressure difference between intake pipe and fuel
pipe, raising the accuracy of fuel injection.
4. By measuring the air pressure of intake pipe, this system gives the vehicle better accommodation to the
environment.
5. Idle air by-pass system supplies fuel and air to stabilize the idle running, and cold starting.
6. O sensor feeds back the signal to minimize the exhaust pollution.
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sensor enhances the efficiency of the catalytic converter,
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