Probable causes of an engine running rich are as follows:
1. Fuel pressure not within specs. Can be cause by restricted fuel return line or defective fuel pressure regulator.
2. Defective Oxygen Sensors.
3. Leaking injectors.
4. Coolant temperature sensor out of calibration.
5. Restricted air intake system.
Monday, May 17th, 2010 AT 12:38 AM