Emissions/Smog Testing S13 SR20DET

[ThatOtherGuy]

I have a '95 240sx with an S13 SR20DET. It's emissions testing time again for me. I've had the engine for about 2 years now and I passed emissions last year but am having problems passing this year. I've got a 2 high flow cats 1 that I got from Heavy Throttle last year and one that I just got this year from Hopup Racing. I got the new one because I figured maybe the old one had gone bad since it didn't pass the first time. However, the new one didn't pass either. I turned the boost back down to the stock 7 psi for testing and also poured a bottle of rubbing alcohol into the gas tank since that burns cleaner. All this didn't make it pass though. It's failing the Nox portion of the test by about 500 in the first test (25/25 or something) and by about 300 in the second test (10/50 or something). I'm in Georgia with an OBD-I car so they only do the sniffer test and nothing else. If I can pass this like I did last year, I'll be fine.

When I put the rubbing alcohol in, I only poured 1 bottle in and I did it when I had a full tank of gas. Should I put more in since that first one probably got pretty diluted? If so, how much more? Also, should I turn the boost down more? Maybe to 5 PSI or something, or does that not matter at all? I'm just looking for some things that I might be able to try. Better spark plugs or something? Like I said, it passed last year and nothing's changed since last year on my car. Also, I don't have the EGR valve on there due to the steering issues when I put the engine in my car as I'm sure you all know. Any help would be great. Thanks in advance.

[SpeedRacer1]

I dont know as much about NOx emissions since we dont have them here, but there are a couple things I could think of that you could try. Basically the problem doesnt have to do with the emissions from a bad engine, its because the ECU tells the car how to run and it usually tells it to run pretty rich. A couple things we do here in WA are get an SAFC and lean things out, or make a switch that turns off the O2 sensor at idle, thus disabling the ECU's ability to run rich at idle. Unfortunately I only know about how to pass when failing HC's or CO, not smog.

[yellow_jacket]

High NOx is a result of high combustion temps. An egr valve would normally help bring this down. You can also retard your timing a little. If that still doesn't do it, richen the mixture up a little.