Probable causes of an engine running rich are as follows:
1. Excessive fuel pressure can be cause by restricted fuel return line or defective fuel pressure regulator.
2. Defective Oxygen Sensors.
3. Leaking injectors and fuel pressure regulator.
4. Coolant temperature sensor out of calibration.
5. Restricted air intake system.
Wednesday, July 28th, 2010 AT 4:26 PM