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1) Yes, your cat is a 3-way.
2) Plug your ignition control module vacuum input for the test. You should find a vacuum line running from the TB over to the ignition control module on the passenger fender behind the headlights (black box with a vacuum transducer at the bottom.) This is a Chrysler ignition computer, and it is of the 'lean-burn' philosophy. It will try to advance the timing up to 52* as soon as you crack the throttle open, and it will hold it as high as it can w/out detecting knock. This makes for excellent mileage and power, but NOx suffers. Volvo issued a recall on this, and fitted some vacuum delay valves to try and correct for it (you may have these installed in the vacuum line, a green/black valve, maybe a black/white one as well.) These really only served to cause a lot of knocking and other unpleasantries. I run my '83 w/out delay valves, as originally intended. But with that background info out of the way, here is what you really need to know - if you plug the vacuum line at both ends, the ignition unit defaults to a very mild, conventional spark advance curve. You'll be down slightly on power, buth the engine will likely sound smoother & quieter, and best of all, your NOx will definitely be reduced! There's no telling if it will be enough by itself, but it's probably worth trying before you do another step.
3) If #2 does not do enough, you can test your O2 sensor to see if it is working properly. If not, get a new O2 sensor.
4) If #3 is not enough, a new cat may be required. That's about all that could be involved.
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Speed Racer, '83 240 R, '74 164 E, '93 940 OL1 (Manchester, CT)
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