Oxygen Sensor Feedback System

Fig. 1 Lambda-sond (oxygen sensor) system:

°�Fig. 2 Lambda-sond (oxygen sensor) system wiring diagram:

This system, Fig. 1, consists of an electronic control unit, thermal vacuum valve, thermal switch, relay, frequency valve, microswitch, oxygen sensor and a pressure differential switch. This system works in conjunction with a three-way catalytic converter and continuously ``fine tunes'' the quantity of injected fuel into the engine. By fine tuning the injected fuel, more effective combustion can be obtained. When the air/fuel mixture is rich, the oxygen content is low. When the air/fuel mixture is lean, the oxygen content is high. The oxygen sensor is located on the exhaust manifold before the three-way catalytic converter and senses exhaust heat. When hot, the oxygen sensor produces a voltage according to the oxygen content. The electronic control unit senses this voltage and grounds the frequency valve in cycles; this is called the Duty Cycle. The amount of time the frequency valve is grounded depends on the oxygen sensor voltage. The frequency valve controls fuel pressure in the air/fuel electronic control unit's pressure differential valve. The Duty Cycle can be measured by connecting a dwell meter to the test point, Fig. 2. In the event the oxygen sensor becomes damaged, the electronic control unit will operate on a fixed Duty Cycle. Under certain operating conditions, a richer air-fuel mixture is needed. To accomplish this, the system has other components which temporarily ground the electronic control unit, resulting in a fixed Duty Cycle, producing an enriched mixture.
When the engine is cold, the thermal switch senses engine coolant temperature and grounds the electronic control unit at temperatures under 59°F.
During cold engine acceleration conditions, the pressure differential switch which is connected to the intake manifold through a thermal vacuum valve, senses intake manifold pressure. During acceleration, intake manifold pressure drops. The switch grounds the electronic control unit for approximately 0.25---1.5 seconds, depending on the rate of engine acceleration. At temperatures below 131°F, the thermal vacuum valve connects the pressure differential switch to the intake manifold. At temperatures above 131°F, the valve closes off the connection between the switch and the intake manifold and instead connects the switch to the temperature controlled ignition advance solenoid.
During full throttle applications, the microswitch located on the throttle control pulley closes and grounds the electronic control unit.