Nox challenges

[John T. Luyster]

I have a 1999 Infinity QX4 that I'm trying to get a set of headers
emission legal (Smog Exempt) in California.  My first test failed
because of high Nox.  This is determined by a formula they come up with
that extends the results out to at least 50K at which point my Nox
exceeded that limit.  (It would pass a standard street smog test no
problem)  After some investigation I found an Infinity Service Bulletin
that suggested adding a ground wire from the intake manifold to the
righthand cylinder head.  Further diagnostics revealved a lazy or slow
O2 sensor at which time I replaced all four.  After this I had the
vehicle sniffed to verify any changes.  The Nox was down substantially.
At this time I set all the SRT's and drove approx. 50 miles to make sure
no DTC's popped up.  Off to the test lab again and failed again with
high Nox.  This vehilce has no mods done to it.  Factory ECU. The only
thing I can think of might cause this high Nox would be the design or
flow of the tube off the header to the EGR on the engine.  Any ideas????

JT