Oxygen Sensors

The MS41.1 system uses a dual (stereo) oxygen sensor control similar to the M60 engine with the DME M3.x system. The exhaust manifolds are split for cylinders 1-3 and 4-6.

The control module considers these groups as banks of cylinders. Each exhaust manifold contains an O2 sensor for monitoring the fuel mixture.

Each input signal is processed separately which allows the MS 41.1 control module to correct minor deviations on one group without affecting the other. The sensors are placed as close to the combustion chambers as possible which enables the MS41.1 system to respond quickly to changes in the delivered air/fuel mixture.







The MS41.1 oxygen sensors function differently from the familiar Bosch type sensors. However, the end result of the O2 feedback system is the same. The control module uses the signals from the sensors to maintain LAMBDA = 1.

The MS 41.1 oxygen sensors are called "Resistive - Jump" sensors.

The probe of the sensor which is exposed to the exhaust gasses is made from titanium dioxide [TiO2] (a semi-conductive material.) When heated to an operating temperature of 600° to 700°C, the titanium dioxide becomes conductive and will allow current to flow, based on the amount of oxygen in the exhaust.




The resistance value of the sensor changes rapidly when the mixture deviates from Lambda = 1. If the oxygen content in the exhaust is high (LEAN MIXTURE), the oxygen molecules will block the flow of electrons through the titanium dioxide. This creates high resistance, or a small voltage drop across the sensor tip.

As the oxygen content in the exhaust drops (RICH MIXTURE), the resistance to electron flow drops and the semiconductive tip allows electron flow, creating a large voltage drop across the sensor.

Two catalysts are employed for exhaust gas conversion along with two additional O2 sensors mounted at the rear of each converter.

The rear sensors are used for OBD II compliance. The rear sensors monitor the efficiency of the catalyst by measuring the oxygen content in the exhaust after the conversion.

The MS 41.1 control module supplies the O2 sensor with a standing voltage of five volts. The module then monitors the voltage drop across the sensor tip as its measure of lambda swing. The voltage signal at the control module will switch between approximately 4.6 to 0.1 volts as the mixture changes from lean to rich either side of Lambda = 1.

Operation of the sensors is monitored as part of the OBD II requirements. The pre-catalyst sensors are monitored for the following:
- Response Time
- Voltage fluctuation
- Switching Time
- Heater Operation

The post-catalyst sensors are monitored for:
- Voltage fluctuation
- Heater Operation

Failure of a sensor in any area of monitoring will cause the Check Engine Lamp to illuminate and the fault will be stored in memory.