Diagnosis

When was the last tune-up? Sounds like its burning more fuel than air-due to black smoke-

Probable causes of an engine running rich are as follows:

1. Excessive fuel pressure can be cause by restricted fuel return line
2. Defective Oxygen Sensors.
3. Leaking injectors and fuel pressure regulator.
4. Coolant temperature sensor out of calibration.
5. Restricted air intake system.