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Originally Posted by idlafie

High NOX readings is the result of your Exhaust Gas Recirculation, (EGR) system not working. You could have a cut, melted or split vacuum line or bad soleniod somewhere in the EGR system...You'll need a Factory Service Manual to trace the lines & fix the problem.

The purpose of EGR (Exhaust Gas Recirculation) is to reduce the NOx emissions by putting a portion of the vehicle's exhaust gas back into the intake manifold so it mixes with the fuel and air in the combustion chamber. Air is mainly made of oxygen and nitrogen (O2 and N2). At temperatures above 1300°C (2372°F), these molecules split apart and rejoin with each other to make nitrogen oxides (like NO, NO2, etc...).

By adding hot exhaust gases into the combustion chamber, you are lowering peak combustion temperatures. The lower temperatures prevent the O2 and N2 from splitting and combining. Even though the exhaust is hot, about 600°C (or 1112°F), it's much cooler than the 1300°C required to make NOx.

In summary, the exhaust adds mass, increasing the heat capacitance of the mixture (i.e. making it harder to heat up the mixture in the cylinder). Peak temperatures are lower, reducing NOx formation, which ultimately reduces smog in the environment.

thank you for explaining the point of the EGR system to me

never knew that