How to bring down NOx levels?

[sleeperalty]

I went to take my emission test today since my test pipe/resonator came in today, and I want to install it. so i figured I would get the e-check before i replace the cat. but, I failed the NOx test.

their limit is 910.0 and I read 1685.6

according to the info in the pamphlet, they say that could be caused by too high a combustion temp. would adjusting my timing be enough to change this so I pass, or should I try something else?

[MagicRat]

If you expect a decent answer, please state the year make and model of the car.

The EGR (Exhaust Gas Recirculation) system reduces NOx. First check to see that the valve is not stuck, is hooked up and is not clogged with carbon.

[INF3RN0666]

Just a point of advice to make help you pass the test on older engines.

An old myth that supposedly helps you pass the test is to fill your tank with Supreme Fuel and run it through, and Ethanol does the job as well. In addition, there is an additive called "Guaranteed To Pass" and that helped bring down my readings.

My 95 Vision which ran for 456000Km had lower readings than my dad's 2000 impala and my mom's 93 cavalier. Funny thing is, it's still running on the old catalytic converter, which has a loose part inside of it because it rattles.

[sleeperalty]

my car is a 94 nissan altima. I did take part of the EGR system apart today, and one tube was completely clogged with carbon deposits. So I cleaned it out, and im about to take it back to the e-check station in a few minutes

[MagicRat]

Originally Posted by sleeperalty

my car is a 94 nissan altima. I did take part of the EGR system apart today, and one tube was completely clogged with carbon deposits. So I cleaned it out, and im about to take it back to the e-check station in a few minutes

Could you post the results, please?

[sleeperalty]

I read higher than before. so Im gonna replace the cat next. if that doesnt work, I gotta get a S-AFC II and tune it to run richer so that i can bring down the level for the test