The following was from my test center last year:
Saturday I took the car for a TestCenter Only smog check on a dynamometer. And if failed badly and is now registered with the state as a gross polluter. The numbers were:
Test1 15 mph 1787 rpm 13.4 % CO2 2.1 % O2 9 HC (ppm) 0.00 % CO
3125 NO (ppm) (689 MAX, 1907 Gross Polluter)
Test2 25 mph 1901 rpm 13.3 % CO2 2.2 % O2 7 HC (ppm) 0.00 % CO
1827 NO (ppm) (706 MAX, 1707 Gross Polluter)
Everything passed the visual and functional tests, including the Oxygen sensor and the EGR valve.

The previous test was two years ago at the same test center and the results were:
Test1 15 mph 1796 rpm 15.1 % CO2 0.1% O2 15 HC (ppm) 0.01 % CO
70 NO (ppm) (689 MAX)
Test2 25 mph 1725 rpm 15.0 % CO2 0.1% O2 7 HC (ppm) 0.07 % CO
47 NO (ppm ) (706 max)

Now admittedly my NOX levels were much higher than yours but I had a completely severed vacuum line that passed the visual inspection. I still think the following suggestion would be worth trying.
"The quickest thing to check would be the PCV cap and the o-rings under it. If that looks OK, do the standard check of all the vacuum lines and intake/TB gasket sealing surfaces with short sprays of carb cleaner with the engine running (listen for a stumble, indicating the carb cleaner was sucked into a leak in the vac system or an unsealed gasket)."
If you have a less visible leak, e.g. on the backside of a vacuum connector, the carb cleaner spray trick will reveal it. If you took off all the flexible lines and vacuum connectors, stretched them off the car looking for cracks, then that is a pretty good inspection. I found a few bad vacuum lines and fittings after I removed them from the car that looked fine with an on car visual. Not all bad lines/fittings leak which is why the spray may help find the culprit better than a visual check.
-sp4149

On the straight vacuum lines I'll replace them today, if anything maybe it will reduce the NOx ppm by 5%. Everybit helps I suppose.


Thanks again sp4149.

Re: Vacuum leaks
If they all check out, don't forget the one going to the brake booster. A bad booster can allow a leak there.

Although the slight cracks in the muffler really won't have much to do with the HO ppm I figured I would call up several exhaust places and get a price including that Cat back since I figured that changing the Cat would help towards reducing the HO ppm.

The average price I received not incuding the one pipe infront of the Cat which I'm told is a dealer item was $1054.00, if I included the one remaining pipe it would be around, $1421.00.
Unbelievable isn't it, remember that this is in Ontario Canada.

Agreed with sp4149 and RedSled. By far the most likely cause of high NOx is a vacuum leak (leading to leanness and high combustion temps)...and we all know those suckers can be very hard to find, as there are dozens of potential leak points.

Maybe you did this already, but get a few cans of carb cleaner, start the car, and take your time spraying the cleaner everywhere a vac leak could possibly occur (the length of every vac line, every vac nipple and connector, the entire surface of the brake booster, around TB sensors, TB to */C mating, */C to LIM, EM to EGR, EGR to LIM, PCV area, FI o-ring seating area, etc.) listening for a "stumble."

I've done that agrazela, and I never noticed any real change in rpm. I did however change about 6-8 of the vacuum lined that weren't 90 degree fitting from factory. A couple actually started to crumble when I was removing them and even had to use the exacto knife to sperate then since the previous owner most likely never replaced them in the history of the car.


Next will be the A/C delco 02 sensor replacement.

In doing more research I came across this statement from more then one auto tech sight, "The hotter an engine runs the more power it delivers, the more NOx it produces." If that'* the case then why would you want to run the car hard to make sure the Cat it nice and hot if the engine produces more NOx at that stage?