Bought my Mazda 3i used and it is getting 15-17 mpg both in town and highway Have checked the tire pressure, air filter, oil change, brakes and there is no check engine light and I have had two different computer scans done with nothing showing. No check engine light!
I had a BG fuel induction cleaning done with no improvement,
Could it be a bad fuel pressure regulator or something that would not trigger a check engine light?
No one seems to know what the problem can be. Any ideas?

 

How many miles on the car? Is it running well otherwise? Any recent repairs or maintenance? Did the car ever get what you considered to be proper gas mileage? Any changes between then and now? Does the wheel alignment feel right?

Suggestions for a car with 30k miles will be different from suggestions for a car with 120k miles, that's why I ask.

Bob

 

A bad thermostat running on the cool side will suck extra fuel. My car has been getting better gas mileage with a 190 degree thermostat compared to a 180 degree. Time for a coolant flush and fill.

 

43,000 miles on the car, bought it used. Runs fine otherwise. Don't know about any repairs before I bought it. Alignment seems fine. Should I have the fuel pressure regulator checked. Could it be something as simple as a bad gas cap?

 

Add a bottle of Techron to the gas tank.