movie 125 s afi Workshop-manual : Page 58

          5. FUEL INJECTION SYSTEM
                                                                            MOVIE S 150i


Oxygen Sensor

Functional description, type and construction
It uses DC-8-16V Battery Power with 4 pins: one power pin, one
heater pin, one signal output pin and one earthing pin. The sensor is
installed to t he front pipe of exhaust pipe to detect the oxygen
concentration of exhaust gas for determining if ECU shall instruct
to increase or reduce fuel supply for meeting waste gas emission
standard of environment legislation. When the temperature of
exhaust is less than 350, the sensing portion can not be activated
and there is no signal output, and ECU will turn on the heater inside
sensor to accelerate the temperature rise of sensor and cause the
Oxygen Sensor to work normally. In normal hours, the impedance
of heater is 8 +/- 1.5 ohm and can be told with multimeter. Output
of sensor after the engine is warmed up is
A/F <14.7 (mixing ratio too thick) >0.7V
A/F > 14.7 (Mixing ratio too thin) <0.18V

Function: Detecting the oxygen concentration in waste gas, the slight voltage signal generated
will be passed t o computer to determine the level of thickness of mixing ratio to feed back to
mixing ratio control and catalyst transformer coordination.


Close Loop System

  Sensor        ECU          Regulator        Engine         Exhaust Pipe (O2 Sensor)

                                                                    In Idle O2 Sensor at the front
                                   Modify A/F
                                                                    pipe of Exhaust pipe


What is Close Loop System

When Electronic Injection System is meeting the following two conditions, it is called Close
Circuit
System:
      with O2 Sensor
      O2 sensor starts to work
When at Close Loop status, O2 Sensor start to detect the Oxygen concentration in waste gas and
feed back the signal to microcomputer control unit for modifying fuel injection to attain the
air/Fuel ratio for full combustion:
 Air/Fuel ratio = 14.7 (equivalent to mixture of 14.7 air and 1 kg fuel)

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