Oxygen sensor, Catalytic converter and Emission.

OXYGEN SENSOR.

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This is referred to as lambda usually found on the exhaust manifold before the catalytic converter. This sensor measures the oxygen within the exhaust stream and outside the exhaust stream, this will signal the ECU that there's a high amount of oxygen or a low amount of oxygen. When the voltage or resistance is high, ECU will then will think its a lean mixture meaning lots of the fuel was not burnt at combustion and when its low, ECU will think its rich meaning all of the fuel was used up in the combustion chamber. This sensor only works when at a certain temperature and is why this sensor has 1 - 4 wires. O2 sensors with 3 or more wires usually have a built in heater which helps it get to operating temperature  faster (two wires heater + and -, two are signal + and -. This sensor tells ECU when to richer the air/fuel mix or lessen the air/fuel mix. There are two main types of O2 sensors zirconia and titania sensors. Zirconia outputs a voltage while the other a resistance with the presence of oxygen in the exhaust stream. Both sensors voltage signals is above 450millivolts (mv) indicates rich and below 450millivolts indicates a lean. With a oscilloscope, the wave pattern of a O2 sensor should fluctuate between minimum of 200mv and less and maximum peak voltage should be 800mv and more. peak to peak should be at least 600mv or greater with average of 450mv. When engine starts cold, ECU will operate in open loop meaning its running off pre-recorded information stored by the ECU until it reaches operating temperature which ECU will run close loop meaning its no long running off pre-recorded reading and running straight of the O2 sensor
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CATALYTIC CONVERTER AND EMISSIONS.

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This is found between the exhaust manifold and the muffler in the  exhaust system. It's job is to neutralise and create a chemical reaction so that the pollutants within the gases that come out of the exhaust is not harm to us and the ozone. Location of the CAT is important as it needs to retain as much heat for effective operation. This contains small parts of rhodium, palladium and platinum and together act as a catalysts. As exhaust gases pass through the CAT the catalysis reacts turning the exhaust gases from HC( hydrocarbon)+N2O(nitrous oxide)+CO(carbon monoxide) to H2O(water vapours)+CO2(carbon dioxide)+N(nitrous). If this is achieved then on a emissions reading machine it would read HC ,O2 AND CO would be low and CO2 would be high and this is ideal and shows that CAT was working and doing its job well. If HC,O2 AND CO were high and CO2 was low it could be seen as its running rich and could also indicate that the O2 is fusing with the NO which makes up NOx so it would be HC+CO+NOx+SUNLIGHT = SMOG and is bad not only for us to breathe but also for the ozone.