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Catalytic Converter Systems | ||||||||||||||||
| In 1975 catalytic converter systems were developed to bring the emission levels in compliance with EPA guidelines. Engine management systems can maintain a consistent air fuel ratio and exact control of ignition timing which allowed the development of the catalyst system. A catalyst is a substance that allows a chemical reaction to take place without itself being changed or consumed. Catalytic converters contain platinum, palladium, and rhodium acting as the catalyst along with oxygen they reduce HC, CO and NOx levels to within acceptable levels.
Catalytic Converters need to be heated quickly and they must maintain a specific operating temperature in order to become active. The high operating temperature is necessary to achieve the chemical reaction necessary to convert HC, CO and NOx into harmless gasses. Most cats are mounted as close to the exhaust manifolds as possible to prevent the exhaust gasses from cooling down. |
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| Catalytic Converter Systems may use from one to four oxygen sensors depending upon the model. On OBD I systems the O2 sensors monitored the exhaust to control A/F ratios. On OBD II systems some sensors monitor for A/F control while others monitor the performance of the converter. | |||||||||||||||||
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| Four cylinder system using one sensors for A/F and one sensor for converter performance | |||||||||||||||||
| Six cylinder system using two O2 sensors for A/F control one for pre-cat and one for post cat monitoring | |||||||||||||||||
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| Oxygen Sensors | |||||||||||||||||
| As you can see, one of the key players in the catalytic converter system is the oxygen sensor. The catalysts, in the converter, needs an abundant supply of oxygen in order to complete the reaction process. The signal generated by the O2 sensor forces the fuel trim system rich and then lean every few milliseconds. This modulation allows a certain amount of oxygen to flow into the converter where it is stored by the catalyst. During the reaction process the stored oxygen is consumed so, it must be replenished every few seconds. Thus the O2 sensor operation is critical for proper catalytic converter operation. | |||||||||||||||||
| Eight cylinder system using two sensors for A/F control and two sensors for converter monitoring. | |||||||||||||||||
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