1995 z28 90,000 miles. Only mods are pace setter long tubes and k&n cai
new parts:
optispark(got it from thepartslady), plugs, wires, header gaskets, intake elbow, coolant temp sensor, o2's(ac/delco), water pump, radiator, egr valve, catalytic converters, fuel filter, alternator.

I only fail nox. 2.0 allowed cant get below 4.0

Datamaster shows my long term fuel both sides at around 112
after the car is warmed up for 5 or 10 minutes.
Fuel pressure holds 38psi after prime. Car started and vacuum line removed reads 44psi. Wot holds 42psi. Idle is about 36psi. Light cruising I have seen fuel pressure drop to 34psi but is usally at 35 or 36psi.

I'm not sure what else I can check or why my nox levels are so high.
new O2's were installed about 4000 miles after header install and only
have 300 miles on them. The o2's cycle rapidly from under .1 to about .9. Not throwing any codes either.

 

NOx is produced by high combustion chamber temperatures. What is your coolant temp under the conditions they would run the emissions dyno test?

The EGR system is provided to control NOx. Is your EGR system working - no vacuum leaks, solenoid opening when commanded by the PCM, valve moving in response to vacuum?

NOx is also produced with lean A/F ratio. The fact its pulling fuel via the 112 LTFT's on the surface indicates it would be running rich if the LTFT's weren't pulling fuel. But that assumes the O2 sensors are reading correctly. While you have replaced the sensors, I would assume you had to use extensions for the Pacesetters. Are they high quality extensions?

You mention "cat converters" - is your 95 a CA emissions A4, because that is the only 95 model with dual cats?

 

Temp during the dyno test was about 210-220. I live in phoenix so its going to really hot the rest of the summer. I have the stock tune and my fans dont kick on until its pretty hot.
I depressed the egr valve at idle and the car stumbles. Datamaster shows while driving that the pcm is commanding the egr to open. I'm not sure how to check if the valve responds to vacuum.

I welded 2 high flow cats into a 3 inch ory. I took the car car to my regular mechanic and he said the cats are working properly. He also told me that there wasn't enough back pressure to open the egr valve. I emailed a mail order pcm tuner and he said it's probably a fuel issue not back pressure issue.

I did add the propper extensions on the o2's. I checked my FPR this morning and it does smell like fuel in the vacuum hose. Could the FPR have anything to do with my problem?

 

You have to attach a vacuum pump, like a Mi-T-Vac to theend of the hose that connects to the manifold. Pulling a vacuum, cycle the solenoid (apply a ground at the gray wire) and see if the EGR valve opens.

Backpressure doesn't open the EGR valve, vacuum does that job. Low pressure in the exhaust system will reduce the EGR mass flow. But with 2 cats in series, it would seem to have a bit of backpressure on the system. The further away from the engine you locate the cats, the lower the operating temperature. They may not be getting hot enough.