By hot, do you mean closed loop? Open loop (cold) will mask many things, plus some cracks may only manifest themselves as warm parts expand, including electrical arcing. If you can find no obvious carbon traces, say inside the distributor cap and the plugs wires are in good condition, you may want to check the color of each spark plug to isolate the cylinder(s).
Though unrelated to the valuable Code 42: vacuum leak? The ECM will try to counter a low vacuum condition with more fuel, hence blackish smoke. If you can duplicate it while stopped, I'd listen carefully for the location, then use carb cleaner spray to isolate it. Particularly, check hoses, fittings and gaskets.
