CA Smog - Failed nox test @ 15mph, passed @ 25 mph ;;

[armaddon]

ok, I took my 1993 240sx hatch in today for a second shot at smog (failed nox last time as well). Since my first test I've replaced the cat, inspected the EGR valve (it works, car stalls out when i lift the diaphram), and even ran the test on denatured alchohol (ran 91 octane til pretty much empty, poured in 2 gallons of denatured alchohol, ran car around til it got hot). I still failed pretty bad with 1612ppm out of an allowed 704ppm @ 15mph.. however, at 25mph i measured 572ppm out of an allowed 738ppm.

I'm at a bit of a loss as to what exactly to do next. The guy at the shop didn't know I was running on alchohol and suggested 100 octane gas and a larger cat - he said mine looked small (it's an oem-style and size bolt on from Bosal that I ordered off rockauto.com). The rest of my emissions were in the green, though hydrocarbons were a bit higher than I would've liked.

After searching around I think I'll check out the rest of my EGR system, but when I looked at all the lines they all looked like they were in good shape. Someone suggested testing the solonoid with a vacuum pump but I don't have or have access to one :\

Should I go pay a shop more $$$ to weld in a larger cat, or give 100 octane (and maybe some alchohol added in) and swap out to some better spark plugs like some iridiums, or do the work and rip apart and swap out EGR parts? I just don't want to shoot myself in the foot and invest what little money I have left in something that isn't going to get me anywhere..

I'll post the rest of my emissions results below:

--==15mph test @ 1695rpm==--%CO2 - 12.3%O2 - 3.3HC - 45ppm of 88ppm max%CO - 0.06 of 0.52 maxNO - 1612ppm of 704ppm max ;;

--==25mph test @ 1875rpm==--%CO2 - 12.8%O2 - 2.7HC - 49ppm of 53ppm max%CO - 0.13 of 0.50 maxNO - 572ppm of 738ppm max

I'm still not well versed enough in catalytic converters or EGR to determine if mine really is doing the job just by looking at the numbers above.. any help would be greatly appreciated.

[180fan]

NOx failure will be usually attributed to the EGR system. One thing that can be deceptive about the hoses at the egr, is that since they get hot, they can collapse under vacuum. vac lines aren't expensive either, so if it's smog check time, it'll be a good idea to start replacing the vac lines to the bpt, the egr and do a tune up before having to go to the test. Another good idea is to have the car running for a while beforehand, so the cat will be nice and hot before you go on the rollers.

[armaddon]

thanks for the reply, I think I'm going to try again after replacing the vac lines, cleaning egr, and getting a bigger cat thrown on. I think I'll also take the shop guys advice and run it on a mix of denatured alcohol/ethanol and 100 octane gas. wish me luck :x