INTRODUCTION - EXHAUST EMISSION CONTROL SYSTEM

3.2 JTS

Exhaust gas oxygen sensor upstream of the pre-catalyzer

Specifications:

the sensor is the LSU 4.2 broad band linear type with a built-in heater and can operate in a range that goes from 0.7 Lambda to the air. Two of this type of sensor are used, one located upstream of the right bank pre-catalyzer and one upstream of the left bank pre-catalyzer; the two sensors detect the residual oxygen in the exhaust gases after combustion. A module integrated in the control unit, shown in the diagram below, is required for the operation of the sensor.

On the left of the diagram it is possible to see the actual part of the oxygen sensor proper, whilst on the right the control module in the control unit can be seen with the two elements connected by means of wiring which is also visible in the diagram.

The information concerning the quality of the exhaust gas is made up of the value of the pumping current lp which passes through the cable connected to pin 6 shown in the diagram in red; inside the module the voltage signal coming from pin 1 is sent to an amplifier where it is compared with a reference voltage of 450 mV, suitably produced at pin 5, by two generators in the module; in stoichiometric mixture conditions, the voltage signal at pin 1 proportional to the quantity of oxygen present in the exhaust gases in the sensor is equal to around 450 mV, therefore the algebraic total coming out of the amplifier connected to pins 5 and 1 is nil (450 mV - 450 mV), therefore the output does not have a pumping current "lp" capable of flowing through the branch circuit connected to pin 6 and arriving at the sensor.

If the mixture strength is not stoichiometric, the voltage coming from pin 1 is not 450 mV, therefore in this case the pumping current "lp" leaving the amplifier is not zero and it flows into the branch connected to pin 6 and on arriving at the sensor pumping cell produces a migration of oxygen ions which re-establishes the balance that existed in stoichiometric conditions; clearly, depending on whether the mixture is weak or rich, the direction of the pumping current changes, in any case the value of the pumping current lp is proportional to how weak or righ the mixture in the cylinder is (was), because it constitutes the current that was necessary to re-establish the actual balance in stoichiometric conditions.

This type of sensor is therefore particularly useful in giving the control unit very precise information on the quality of the combustion and, especially, its outcome, allowing the control unit to make very accurate corrections to the carburation. There is an internal electrical heater, for optimum operation of the sensor, connected to pins 3 and 4 which is designed to keep the internal operating temperature optimum. There is a sensor calibration resistance inside the connector, connected to pin 2, designed to calibrate the sensor during production in a controlled atmosphere; a feature of the connector is the small Gore-Tex area through which reference air required by the sensor for correct operation can flow via the wiring.

The wiring diagram below illustrates the connection with the engine management control unit.

1. Lambda sensor upstream of pre-catalyzer cylinders 1, 3, 5 (right bank)

2. Lambda sensor upstream of pre-catalyzer cylinders 2, 4, 6 (left bank)

3. Lambda sensor downstream of pre-catalyzer cylinders 1, 3, 5 (right bank)

4. Lambda sensor downstream of pre-catalyzer cylinders 2, 4, 6 (left bank)

5. Engine compartment junction unit

Typical curve for sensor pumping current

The graph below shows the variation in the pumping current depending on the Lambda value which notifies the control unit whether the mixture is rich or lean.

Exhaust gas oxygen sensor downstream of the catalyzer

Specifications:

The exhaust gas oxygen sensors downstream of the catalyzer have the task of diagnosing the efficiency of the cztalyzers on the exhaust pipes. Two sensors are used, one downstream of the catalyzer for the exhaust pipe for the right bank cylinders and one downstream of the catalyzer for the exhaust pipe for the left bank cylinders. The connector has four pins; the wiring diagram showing the connection with the engine management control unit is illustrated below.

1. Lambda sensor upstream of pre-catalyzer cylinders 1, 3, 5 (right bank)

2. Lambda sensor upstream of pre-catalyzer cylinders 2, 4, 6 (left bank)

3. Lambda sensor downstream of pre-catalyzer cylinders 1, 3, 5 (right bank)

4. Lambda sensor downstream of pre-catalyzer cylinders 2, 4, 6 (left bank)

5. Engine compartment junction unit