they started emissions testing in a lot of new counties in texas, and now my dad is having a problem with his mazda 323. It is a fuel injected 4 cylinder with 100,000 some odd miles.
It won't pass just because the NOX emissions are too high.
What causes NOX emissions?
How do you reduce them?
He told me he replaced the pvc, fuel filter, and air filter.
I had him add 2 bottles of heet to it and a couple of gallons of premium gas and drive it around. He will try it again tommorow, but if it doesn't work, he will swing by and I will see what I can do.
What else is there to try?

High combustion tempreratures.  Most likely is clogged or stuck closed EGR valve.  Possible timing if not computer controlled.

Damn emissions laws!  Move!

Your chamber temps are too high.

Your car probably is running to lean.(lean is when the air/fuel mixute is to much on the air side)

Honestly, the easiest way to pass this test is take the test on a colder day.

MickyMouse-The only place I might consider is vermont, but my wife won't stand for moving to a cold climate.
and there doesn't seem to be an egr valve available for it. Checked napa and autozone.


MurderSHO45- If it doesn't pass tommorow with the alchol trick, I will check the plugs and see if it is burning lean. Thanks.

Make sure you update this post when you find out.

THX

I just got off the phone with my dad, and it does sound like he adjusted it too lean. He did the carb adjustment trick,but didn't go far enough. Turn it down till it runs rough, and then pull it up till it runs okay. Only he didn't tweek it the extra half turn.
He will turn it up, drive up in the morning when it is cooler before they open so the car can cool down, and try again. If it doesn't work, I will work on it tomorrow night and will update when I am done.

There are four promary causes of NOx emissions (NOx, BTW - is "Oxides of Nitrogen."  NOx is a contributing factor in Acid Rain, and it not the same thing as Nitrous Oxide, either.)

Lean mixture - when the mix is lean, combustion temperatures rise.  When the mixture is correct ("Stoich") or slightly rich, some of the heat energy in the combustion chamber is released as the fuel droplets in the chamber are evaporated.  Even with fuel injection, there are droplets in the atomised fuel mix.

Thermostat too hot or not flowing enough - This will delay the beginning of cooling the chamber walls, and will also manifest as a higher base coolant temperature.  Not cooling the cylinder enough will also result in higher chamber temperatures.

High Mileage - with smaller engines especially, high mileage engines build up a layer of hard soot (carbon deposits) on the face of the combustion chamber in the head, the valve heads, and the piston head.  This not only raises the base effective combustion ratio (resulting in a higher initial temperature!) but also slightly insulated the only cooled part constantly exposed to coolant flow - the head.  Running a cleaner to knock the Carbon deposits out can help - but disconnect your catalytic converter while you are cleaning to prevent clogging.  Replace or reconnect after cleaning the chamber

Spark Plug too "hot" - Spark plug heat refers to the length of the path that heat must take to leave the spark plugs.  Hotter plugs have a longer porcelain nose behind the threaded collar, and retain more heat.  Going to a "colder" plug (shorter path) can help to minimise this.  If you parts guy is worth a damn, he will know what to get you.

Note the common factor in all these - HEAT.  An EGR valve is supposed to help with NOx, but it is not a substitute for real engine tuning.  Pity they force these things on us, as EGR valves are directly responsible for increases in CO and HC emissions due to imcomplete combustion (contamination of fuel.)  Many devices on an engine designed to reduce a particular emission gas result in an increse in all the others...

BTW - Find a dealer for Beck/Arnley Worldparts - they may have an EGR Valve for you...

FFZ

How close are you to passing?  If close add a pint of rubbing alcohol to five gallons of gas and get the catalytic converters hot, meaning make sure you drive the car a bit before you go in for a test. I have found NOX failures to  usually  be a bad converter, wornout engine, or timing screwed up.

Thanks guys for all your help. My dad called and said it passed.
We tweeked the mixture up a little, and they guy at the inspection place had to tweek the timing a little, but it finally passed.