1991 Dodge Ramcharger, black smoke from the exhaust pipe?

What have you checked so far? Do you have a scanner that displays live data? Is the Check Engine light on? Have you checked for diagnostic fault codes?

I have checked the fault codes, oxygen sensor. The check engine light has not come on.

What was the exact fault code number or description. Any defect that could have an adverse effect on tail pipe emissions must turn on the Check Engine light when that code sets. That includes all oxygen sensor codes.

Does your Check Engine light turn on for six seconds when starting the engine? If it doesn't, it could be burned out.