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1995 Chevrolet Camaro Z28 failed smog test for high NO (PPM) why?

1995 Chevrolet Camaro Z28. It recently failed a test only smog check. The only category that I failed was the last one, NO (PPM), it ran high compared to the average. What would cause this?
Answer:

Your Camaro could have failed for high NO due to two things mainly. The first would be a defective EGR system or the EGR valve. EGR stands for exhaust gas recirculation. Your Camaro's EGR system includes the EGR valve, EGR control system and EGR ports/passages. Your Camaro EGR system recirculates burned up exhaust gases back into the combustion chambers. This allows the engine to run cooler and keeps NO levels within limits. The EGR valve should normally be inspected to ensure its proper operation. Carbon deposits often plug up the EGR passages and cause the valve to stick. The second problem which could be causing your Chevy Camaro to fail for high NO is lean fuel or lean air to fuel mixture. NO is created when an engine's combustion chamber temperatures rises above 2500F Fahrenheit. When not enough fuel gets to the engine a lean fuel condition is created causing the engine to run hotter then normal and creating NO. The lean fuel conditon should be seen in the CO numbers on your VIR report. Anything between 0.00 and 0.03 percent CO is too lean and needs to be diagnosed. posted by SmogTips Support

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