Originally Posted by Soccerluvr4
Make sure your A/F ratio is good, running rich you are just wasting fuel, and mustangs generally run slightly rich from the factory.
Thats the whole point of electronic fuel injection. Electronic fuel injection was developed to have input data turn into output data, these two forms of data help the computer achieve a stoichiometric air fuel ratio. Basically what this means is you have 14.7 parts fuel to 1 part air, the best optimal conditions for a gas engine to combust.
Any abnormal data from either of your input and or output sensors will cause this ratio to change in your engine. Most of the time these changes will emit the CEL, however if the data isn't "abnormal enough" it will not. Also, whenever your CEL is on your cars engine is in a default called "limp mode". When in limp mode your vehicle will richen up the fuel a great deal to save you from burning up your motor. Double edged blade there as well with leaving CEL on. Run rich for too long and foul out plugs, kill o2 sensors cat converters, ect.