My HC measures 0 and 0 (83 and 48 allowed), CO is .01 and .01 (.48 and .46 allowed)... But my NO measures 1091 and 1015 with 689 and 706 allowed... In my first test a month ago my NO was 931 and 856 - I fixed my header leak and the results actually got worse...

I think I know what to do but I'd appreciate any input. I've ordered new O2 sensors from Jason Cromer - I had a header leak for a few years and figure the O2 on at least the passenger side is fouled up. Is there another O2 after the cat on 94's? If so, should I replace this also?

I'll remove and clean the EGR... I understand that these two things (O2's and EGR) are the most common culprits for failing the NO portion of the test - anything else I should be wary of?

My K&N intake filter hasn't been cleaned in about 5 years, guess I'll "recharge" that while I'm at it... Any advice is welcome. TIA.

 

Sometimes a bad cat can cause high NO readings and good everything else. It would also explain why the readings went up after you fixed the header leak.

 

I think the air pump plays a role in NO reduction. You might want to check the functionality of that.

 

high Nox readings are caused by high combustion temps

that can be assocaited with a lean a/f
too much carbon build up on the tops of your pistions can raise compression and thus raise combustion temps too

but i would check your egr as it is there to cool combustion temps while crusing and reduce nox

also check for vaccume leaks and the o2 sensors to get rid of the lean condition

i have heard of probs with random-tech cats and failing for nox but your cat appears to be good by your other readings

good luck hope this helps
any other ? ask
Eric