Oxygen Sensor Feedback System
General
This is a self-adjusting engine control system designed to reduce emissions and improve fuel economy. An exhaust gas sensor, (oxygen sensor, also called Lambda sensor, or Lambda Sond) monitors the oxygen content of the exhaust gases leaving the engine. The exhaust gas analysis is fed into a closed loop feedback system. This continuously adjusts the air-fuel ratio to provide optimum conditions for combustion and efficient elimination of all three of the major pollutants (hydrocarbons, carbon monoxide and oxides of nitrogen) by a 3-way catalytic converter.
IMPORTANT: Small amounts of lead are sufficient to damage the Lambda Sond. Unleaded gasoline must be used at all times.
Advantages:
- Allows nearly 100% combustion by the catalytic converter.
- Relatively clean exhaust gases.
NOTE: Not all components appear on all models; designs may vary.
Lambda Sond (Oxygen Sensor)
Measurements are taken by a ceramic sensor in the Lambda Sond. It produces a small voltage (90 - 100 mV) in proportion to the difference between the oxygen content of the exhaust gas and the oxygen content of the ambient air. Exhaust gases heat up the sensor which begins to operate at 350°C = 660°F. In some models the oxygen sensor may not heat up quickly enough to the operating temperature of (350°C - 660°F) due to lower exhaust gas temperatures. This means some Lambda Sonds are heated by an electric element. Heated Lambdas are found on the following engines: late 1984 B23F, and all B230F.
Fuel Injection Control Unit
Monitors various sensors and controls:
- Engagement/disengagement of main relay (current supply to control unit, injectors, etc.)
- Fuel supply by varying injector open time.
- Idle speed by varying air control valve opening.
Control unit incorporates a micro computer.
The output from the oxygen sensor is fed into the control unit.
This device supplies a control current to the frequency valve. The control current has a set frequency and operates by varying the duty cycle.
When the oxygen sensor is cold, or defective, a "fixed control" program is engaged after approximately 5 - 10 seconds.
Legend:
A Input Signals From Sensors
B Converter
Converts each signal into digital form which can be interpreted by computer.
C Input And Output Section
Controls information flow in computer.
D Micro-Processor:
- Compares air input and engine speed input to information stored in memory
- Calculates amount of fuel to be injected
- Adapts these values with regard to impulses from other sensors
E Memory
Contains precise information on appropriate fuel quantities and ignition timing for different air masses and engine speeds.
F Converter
Converts signals from micro-computer to voltages for control of system relay, injectors and air control valve.
Frequency Valve
This device influences the fuel flow by varying the pressure on the underside of the diaphragm in the pressure-regulating valves of the CI fuel injection system.
The frequency valve operates on a set frequency and by varying the ratio of closed to open times in the circuit.
Lambda Sensor Reminder Light
Non-heated Lambda Sensor only.
Indicator light on the instrument panel which is activated at 30,000-mile (50,000-km) intervals. When light is activated, Lambda sensor should be replaced.