Updates:
Bought the tool to adjust the mixture screws. The plugs had already been knocked off, and I found one screw at one turn out, and the other at three turns.
Since I’m trying for a richer mixture to bring the NOx down from over 1000 (max permissible is 783/791..see below ), I set the screws at 4 turns each and set the MCS dwell at 30.
Failed again with nearly the same results.
The tech suggested I take another look at the EGR system, including driving with a vacuum gauge connected to the EGR solenoid output port via a long vacuum hose.
Voila, no vacuum signal. Checked the hose from the carb to the EGR solenoid and got up to 14 vacuum at part throttle.
So the EGR solenoid appears to be at issue. Can someone please explain how the solenoid is supposed to work?
Logic tells me the ECM would tell the solenoid to close when the engine is cold, then allow vacuum to pass when at operating temperature. If that’s so, when would voltage be sent to the solenoid?
I’m tempted to bypass the solenoid and connect the EGR directly to the carb ported vacuum and test it that way to see if a functioning EGR lowers the NOx. It wouldn’t pass visual inspection, but at least I’d know whether I need to spend $800 on a cat or start searching for the unobtainable solenoid.
TIE and Dave, thanks for hanging in there on this!