This doesn't make any sense. If you really think you are getting a "better" burn, your o2 sensor would show a leaner reading more often, causing the long term fuel trims to adjust to compensate. That's quite possible if spark performance has actually improved. But if the car is making more power, you would be using less throttle to get the same driving performance as before, negating any effect the fuel trims might have. If you are getting worse gas mileage, it's because your driving has changed or there is some other unrelated negative factor.Originally Posted by anothernord