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1987 Mercury Sable 3.0 6 cylinder engine failed smog test for high NO.

My Mercury Sable v6 recently failed the smog test because of high emissions. The NO (PPM) max was 573 and the ave was 407. My Mercury Sable measured out at 1032. I dont know where to start looking first to find the problem.
Answer:

There are several reasons why your Mercury Sable could have produced high NO. The most common is your Mercury's EGR system. The EGR valve in your Mercury Sable is responsible for re-circulating a small amount of exhaust gas back into the combustion chamber. This is done to cool down the chamber temperature by producing an inert gas along with the regular fuel mixture. Nitrous Oxides emissions are formed when engine chamber temperatures rise above 2500* F. Keeping the chamber cool reduces NOx emission. The second most common cause for high NO are lean fuel mixtures. A lean fuel mixture is when the engine receives less fuel then is necessary to obtain efficient combustion. Lean fuel mixtures are often due to vacuum leaks or defective fuel control. A smog check repair shop will have to ensure your Mercury Sable is in proper fuel control. They will have to inspect the fuel injection "feedback" system and ensure the engine computer is sending the correct signals to the fuel injectors to either increase or decrease fuel delivery to the combustion chambers. When the engine doesn't get enough fuel NO emissions are increased. posted by SmogTips Support

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