To high Nox

[CSH-HQ]

By reducing the backpressure, the engine less EGR's itself.
This self egr is from when both valves (intake+exhaust) are open at overlap.
So seems like your system is not restrictive enough.  Might they be using 
some of the exhaust backpressure to further open the egr valve?.
Just somethin to think about.
Bruce

>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
>