Gas leak

You can have it check with an emission testing place or you have to physically check it -start at the fuel tank and end at the fuel rail-Or could be just running rich due to the following:

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.