Now that I've looked in the service manual a bit, I see that I should be getting a code 45- Rich HO2S signal indication. With that much black smoke, the computer should have set code 45. Since it didn't, I'm thinking there is a problem with the oxygen sensor or it's wiring.
I've never replaced the O2 sensor and the car has 132K on it. With the (lack of) maintenance I've seen on this Rodeo, it could be original. Check / Replace interval is 60K miles.
Dale