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.
6. Vacuum leak
Saturday, December 3rd, 2011 AT 3:45 PM