This is my 2nd attempt and failed again. First time I took it to the shop I thought nothing of it since the car is all stock. 2nd time around I did a full tune up; plugs, wires, cap, rotor, oil, oil filter, air filter, fuel filter, pcv valve, replaced all vacuum lines, ran a bottle of crc guarantee to pass formula, checked timing, ran car on freeway at 80mph for 20min, took it in and still failed.

1st guess is that it could be my egr valve. There is an exhaust fume odor I can sometimes smell while sitting at a stop light, and I can sometimes smell it while getting out of the vehicle, right between where my door and the hood meets. The egr valve could be getting stuck open?? Or there could be an exhaust leak?? I won't have time to diagnose/clean this problem until Thursday, until then I would like some feed back on what could cause me to have high NO.

2nd guess would be my Cat.

What are your thoughts on this?

 

I'd check first for exhaust leaks then cat. Mine had high nox (2,4xx) and it was the cat.

 

What car and engine?

The engine is running very lean. This is the problem. Have you replaced the fuel filter already?

 

It's a '90 CRX HF, all stock. Yes, the fuel filter has been changed, so has everything else associated with a tune up.

 

Measure the fuel pressure and test the FPR.

Also check the ignition timing.

 

Its most likely your CAT! Changing your O2 sensor could help?

 

check for exhaust leaks, clean egr passage, check o2 sensor, check cat. (cheapest to most expensive)

 

These^ are two good ideas. Check the O2 sensor by unplugging it. The engine should now run rich rather than lean in an emissions test.

 

its not the cat with HC that low, its most likely your egr system. with the CO measures that low you are running VERY lean, CO of 0.1% is 14.72:1 air to fuel ratio.
clean your egr ports and possibly replace the o2 sensor.