My high NOX was caused by bad cat and leaky air intake accordion hose. Also timing was off...
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'88 245,M47,Virgos,235K+

I also am subject to CA smog checks. Search the board, I recall reading some posts on the subject of high NOX. This was attributed to air being sucked/getting into the exhaust system just upstream from the cat. converter. Air enters through cracks in the exhaust manifold, [i.e. cracked manifold] or bad exhaust manifold gasket or bad gasket where the manifold joins the exhaust pipe. The indication that your NOX readings went up after replacing parts could indicate in the process of replacing those parts things may have been tweaked, crack enlarged, gasket warped etc., such that more air is entering the system, hence higher NOX reading despite all the new parts. Listen for the sound of exhaust escaping on the right side of the engine.
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1988 245A. Past: 1979 245A; 1987 244 M47; 1971 164E