['stang princess]

I have a 1990 2.3 L mustang. My parents are currently using the car and my dad recently took it to get it smogged and it failed. He told me that the tech guy told him the "NOX" was what failed and that it was about 100ppm over the limit. I dont know much about smogging or if that is even anything a car coluld could fail for but does anyone have any ideas as to what i could check to see why it failed so i dont end up spending a crapload of money for some mechanic to ifx what i could? thanks!

[mustanghelper]

buy some guarantee to pass emission stuff for 10 bucks and follow the directions, and yous hould pass by 100ppm.
Or spend 10 times more for a complete tune up.

[Charles M.]

High NOx is often due to lean burn conditions at idle. I failed NOx with an '88 5.0. I replaced the fuel filter, plugs, distributor rotor and cap to correct weak spark at idle. It easily passed.

YMMV.

[b_chandler]

NOx (Oxides of Nitrogen)

WARNING>>> CHEMISTRY LESSON AHEAD


Nitrogen and Oxygen are in the air we breathe. They exist as seperate elements and as long as they stay that way, the sky won't fall and Al Gore is happy. Our cars breathe the same air with the same N and O content. As long as the engines combustion temperatures stay below somewhere around 2000 to 2500 degrees F. N and O stay separated. Just above that temp, N and O combine chemically to create oxides of nitrogen (NOx) one of the main ingredients in smog.

Two probable causes for high combustion temperatures are a stuck or clogged EGR system or a lean air/fuel mixture. Lean A/F can be a bad O2 sensor, bad fuel filter, vacuum leaks, improper air intake measurement.

I'd check the tube and passages on the EGR system. Check the valve to make sure it's working properly, and make sure there's no gunk clogging up the works. That's the easiest place to start. After that, you're looking for reasons for too much air, or not enough fuel.

['stang princess]

Yeah, It failed at both the of the RPMS they test it at, does that make any difference? whats the pass smog stuff?

[74stang2togo]

There's a product available at most auto parts stores made by CRC chemical called "Guaranteed to Pass" or something like that, it's a fuel additive that essentially cleans the carbon out of the engine much like any other fuel injector cleaner, as well as having a few extra additives to alter the chemical composition of what comes out of the tailpipe.

[evintho]

Princess, the bad thing about living in California is, we've got the toughest smog laws in the country! The good thing about living in California is, we've got the CAP program! Consumer Assistance Program sponsored by the state. If your car fails smog, the state will pay up to $500 to have it repaired! There are a few criteria that have to be met but surprisingly, income isn't one of them!

If it's says on your registration that the DMV sent you, your car needs to be smogged at a 'test only station', you've met the criteria. Because your car is a '90, chances are pretty good it's a test only candidate. Simply go back to the smog tech and ask for the CAP application. Fill it out and send it in. Takes about 6-8 weeks (typical bureaucratic bs). DMV will give you a red temporary sticker to put in your back window so you can drive the car. When that state sends you back the approval, take the car into a Gold Shield smog station (they'll give you a list) and have it fixed. For $500 they can do alot! If your income is under something like $30k, there's no charge at all. If you're over that, there's a $100 deductible. All in all, a great deal! I've personally done it twice! Good luck!