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1986 Ford F-150 failed smog test for high NO. What causes high NOx on my Ford?

I already have $180.00 into this. New air tab valve, new tab pad seal, set timing, new gas caps. New motor installed in 3/6/08 15600 miles. Maybe the guy who changed the NO max from 1120 to 784 can clue me in on the magic part that's supposed to reduce my Ford's NO in 1064 in 2008, to 1032 currently, or 855 with the timing retarted as much as this situation. I know the state is willing to give me a whopping 1000.00 to retire my truck but I'd like to keep my Ford.
Answer:

There are a few reasons your Ford F-150 could have failed NO. The most common is the malfunctioning EGR system. Your Ford's EGR valve 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 EGR valve on your Ford should be inspected to ensure its proper operation. A working valve should be able to open its passage using manifold vacuum. Manifold vacuum is created during the engine's intake cycle. The high demand for air during this cycle creates a vacuum within the engine's intake manifold. The EGR system is prone to collecting carbon build-up. Since the EGR valve pulls exhaust gasses from your exhaust and introduces them back into your engine's intake air over time it will become clogged or stuck open/closed from the carbon deposits. It is possible to clean the EGR valve if you remove it from your vehicle and either spray it out or let it sit in regular gasoline. Lean Fuel Mixtures - Lean fuel mixtures cause high NOx also. If your Ford F-150 is running lean (indicated by low CO emissions) high NO would result. 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. These leaks will allow the suction of additional and un-metered air into the combustion mixture or exhaust (depending on where the vacuum leak is located) disturbing pre/post fuel combustion and increasing NOx emissions. Vacuum leaks are often hard to diagnose as they may be present at locations not easily viewed. We have to recommend you have a smog check repair station first inspect your Ford's EGR system, and then ensure the fuel feedback system is functioning properly. posted by SmogTips Support

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