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.