Everybody is looking for ways to get better gas mileage from their cars. As gas prices climb towards and above $4 a gallon, this search for better mileage is reaching into ECU program modifications. There are a few different ways to accomplish this. You can program the ECU to allow more air into the cylinders, while keeping the amount of fuel the same. This will produce more power per unit of fuel. You can also make changes to the programming to change the ignition spark timing. Advancing the timing by a couple of degrees will help your engine make more power, while using the same amount of fuel per revolution.