Engine runs rough and doesn't seem to have full power on 2000 Ford Excursion

Engine runs rough, doesn't seem to have full power, exhaust smells funny, and tail pipe is black.

Asked by for the 2000 Ford Excursion
Is the check engine light on? If so, the controller has detected malfunction in the engine and emissions management system and has data and trouble codes stored which woulod be useful in diagnosing your vehicle. If no light on, could be the exhaust is restricted, maybe at the catalytic converter. Also possible that the intake air filter is restricted by too much dirt.
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