My gf's 1994 Accord LX automatic with 115K miles, ALL STOCK, failed smog with High Nox. This is her daily driver and trusty commuter car. You'll see from the graph below that the car did fine under HC and CO, but under NO, it was over a bit at 15mph and just squeaked past at 25mph.

We drove the car pretty much all morning and we didn't have to wait to be smogged so the car was definitely hot enough.

After searching people mentioned anything from cleaning out the EGR valve, to swapping out spark plugs, air filter, oil change, cat, O2, etc. Before I do anything, I want to hear from some of the experts we have here in H-T

 

Not sure what all the number mean, but a few little things can help you with the test.

Cleaning the EGR is one (as you said) Changing the sparkplug would do a little (if you haven't changed it in years) I would put in Seafoam in the tank and into the vacuum line. Just to get rid of any carbon. Of course do this before you get a smog check.

On my 96 Accord, Honda had this Emissions warranty Extension Recall. It was for 95-97 Accords and some other cars. They replaced the distributor, wires, sparkplug and some other things for bringing the car in. You might wanna check those.

 

The most common cause for increased NOx emissions is higher than normal combustion temperatures, this can be caused by a malfunctioning EGR system, engine overheating, compression too high because of carbon build up, or misadjusted timing.

in the case of most accords your timing is not the problem. Unless your headgasket is blown, or you have a bad radiator I wouldn't think overheating is the problem either. so this leaves carbon build up and your EGR system. Like the kid said run a little seafoam or any generic fuel system cleaner to temporarily fix the carbon build up issue.
If you havent already you must clean your EGR ports. This was more than likely the cause of your NoX failure. There is a write up in the Accord FAQ forum on how to do this. And yes, you may want to run colder spark plugs......but most of the time this doesnt help.

 

Thanks for your responses.

You're right, the headgasket isn't blown and the radiator was replaced within the past year so that's the not the probelm. Looks like the I"ll be attacking the EGR ports. Appreicate the direct responses