1993 Explorer 4.0l runs when check engine light is on

I just changed engine in a 93 Explorer 4.0l, a/t.

The new engine runs great when cold. Once thermostat opens it runs great ONLY when check engine light is ON. Once light goes out, then it runs and idles rough - like it is just dumping fuel. The exhaust is black.

Have only drove about 30 miles max.

Please provide suggestions.

The new engine was also from a 93 Explorer.

Please advise.

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