NOX or Oxides of Nitrogen are produced when the peak temperatures in the combustion chamber are extremely high. It contributes to the dirty brown color in smog. This is usually the result of a failed EGR or plugged EGR tube. The EGR(Exhaust gas recirculation) re-introduces exhaust gases back into the engine, under certain conditions, to reduce peak temperatures in the combustion chamber. Repair the EGR and/or clean out the flow tube(s) and this should fix your problem. If not, you might have too much carbon build up in the engine which will actually increase compression and temperatures and you might need to perform a top engine cleaning. I hope this helps.
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NOX or Oxides of Nitrogen are produced when the peak temperatures in the combustion chamber are extremely high. It contributes to the dirty brown color in smog. This is usually the result of a failed EGR or plugged EGR tube. The EGR(Exhaust gas recirculation) re-introduces exhaust gases back into the engine, under certain conditions, to reduce peak temperatures in the combustion chamber. Repair the EGR and/or clean out the flow tube(s) and this should fix your problem. If not, you might have too much carbon build up in the engine which will actually increase compression and temperatures and you might need to perform a top engine cleaning. I hope this helps.