In many car fuel feedback control systems, not only is an oxygen sensor installed, but the Ford 3.8L V6 model, manufactured in 1980, has been equipped with two oxygen sensors. In order to adapt to the constantly strengthening EPA's exhaust gas control requirements, the number of systems using multiple oxygen sensors is constantly increasing. The number of oxygen sensors on cars continued to increase in 1988 and later. In addition, since 1994, some cars have been equipped with oxygen sensors in front and behind the catalytic converter. How can the OBD II system installed on the car be used to check the performance of the catalytic converter, and in some cases, it can also increase the accuracy of air fuel ratio control. In any case, the fast signal of oxygen sensors makes them one of the most valuable diagnostic tools for engine performance. The more oxygen sensors there are, the more beneficial it is for maintenance technicians.
Usually, the engineering logic of fuel feedback control systems determines that the higher the accuracy of fuel control, the closer the oxygen sensor is to the combustion chamber. This is mainly determined by the characteristics of the exhaust air flow, such as gas velocity, channel length (gas instantaneous lag), and sensor response time. Many manufacturers install an oxygen sensor under each exhaust manifold of each cylinder, which can determine which cylinder has a problem. This eliminates the possibility of diagnostic errors and in many cases reduces diagnostic time by eliminating at least half of the potentially problematic cylinders. Using a dual oxygen sensor to monitor a functioning catalytic converter, coupled with a fuel feedback control system that controls the fuel distribution system, can ensure the safest conversion of harmful exhaust components into relatively harmless carbon dioxide and water vapor. However, the catalyst may be damaged due to overheating (such as poor ignition, etc.), resulting in a reduction in the catalyst surface and sintering of the orifice plate metal, Both of these will cause permanent damage to the catalyst.
When the catalyst fails, it can be known that technicians are very important for repairing the environment and exhaust gas system.
The emergence of the OBD II diagnostic system provides precise detection methods for the environment and catalyst onboard monitoring system, as well as the OBD II monitoring system based on the oxidation characteristics of good or bad catalysts. During stable operation, a good oxygen sensor (hot) behind the catalyst should have much less signal fluctuation than any oxygen sensor before the catalyst. This is because the catalyst that operates normally consumes oxidation capacity during the conversion of hydrocarbons and carbon monoxide, which reduces the signal fluctuation of the rear oxygen sensor.
The signal fluctuation of the rear oxygen sensor is much smaller than that of the oxygen sensor. It should also be noted that when the catalyst is turned off (or reaches operating temperature) and the catalyst begins to store and use oxygen for catalytic conversion, the signal increases due to the decreasing amount of oxygen in the exhaust.
When the catalyst is completely damaged, its conversion efficiency and oxygen storage capacity are lost. Therefore, if the oxygen content in the exhaust gas at the rear of the catalyst is not complete, it is very close to the oxygen content in the exhaust gas at the front of the catalyst.