Air By-Pass Valve; Fuel Injector; Fuel Pump - Sym ATTILA RS-21 EFi 150 Service Manual

Air By-pass Valve

Air by-pass valve
Description:
The ECU that received all sensors' signals to control the throttle valve openness with PWM so that
can adjust air-flow into the by-pass valve of the intake manifold. And then adjust idle speed and have
a stable and normal running engine.
1. When engine starting---the by-pass valve open for a while to increase air-flow and then enhance
engine idle speed to prevent from unstable engine running and misfired within initial starting.
2. Warm-up---when engine oil is in low temperature condition, the by-pass valve adjusts air-flow
according to engine temperature (engine oil temperature) so that have a fast idle speed.
3. Speed Decreasing---with the ECU controlling, the by-pass valve also corresponds with
acceleration operation to provide intake manifold with proper air-flow quantity. Such operation
will let engine rpm reduce slowly to prevent from engine misfired, negative pressure in intake
manifold increasing, and then to reduce HC emission.

Fuel Injector

The 2-hole fuel injector provides two intake valves with one fuel injection so that can reduce HC
emission. A short mounted nut can lock the fuel injector easily and receive fuel from the fuel pump.
The mounting bracket can limit the fuel injector rotation in left or right motion. The fuel injection
quantity is controlled by the ECU signal. The fuel pressure regulator can keep pressure difference in
between fuel pressure and manifold vacuum around 2.5bar by means of diaphragm and spring.
Therefore, with such operation, the fuel injector can control its fuel injection quantity by injection width
(time) under different engine loads.

Fuel Pump

The electrical fuel pump is powered by battery and controlled by the ECU for on or off. The pump can
output 14 l/h fuel quantity in 2.5 bar.
This chapter Contents
4. FUEL INJECTION SYSTEM
Fuel injector
TPS
air temperature
engine oil temperature
engine speed
ECU
manifold pressure
throttle openness
4-15