90 LS400 NOx Emission Failure - Happy Ending

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My state limit for NOx was 875PPM... The car FAILED with 975PPM... Strangely
enough, the HC and CO were WELL BELOW the limits and I never experienced and
Engine Check Light activity.

The EGR valve is attached to the manifold with a little "adapter" which
directs the output of the EGR value through a (cooling?) channel before
directing into the engine (manifold).  That channel was (almost?) completely
blocked with rock hard black carbon.  Using a dremmel tool to grind it out
and a shop Vac to suck out any loose debris, THEN cleaning the EGR valve
(and vacuum modulator/filter ) with a little carburetor spray ... and I was
back in business!  Retested at 717PPM.  My highway MPG has always been
~25MPG, but my local MPG was pathetic ... The local MPG seems(?) to be much
better now and Highway is getting ~26MPG.  The car NOW idles at higher RPM
until warmed up.

230K
j



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