I cleaned the MAF with MAF cleaner (it looked very clean) and added fuel system cleaner. I will run this tank of fuel down to <1/8 and refill and zero mileage recorders. I will report back in ~ 2 weeks. Ed
Follow up. I have run a full tank(299 miles) of fuel through my CX5. The results are: Dash read-out=26.7mpg average vs 26.97 mpg calculated for a difference of only 0.24 mpg. No explanation for the original discrepancy except a possible id10t error. Ed
That, along with new tyres with a slightly different overall diameter and even tyre pressures that havent been checked for a while, dirty engine air filter or even dirty fuel filters, are likely to be contributing factors.
A change in tire diameter, whether due to different sized tires or inflation pressures, won't make a difference in how the vehicle calculates mileage. The computer can use the wheel speed sensors (which will measure wheel rotations) or a vehicle speed sensor on the transaxle (which will measure the speed of the drivetrain) to calculate the speed of the vehicle, but has no way of knowing the actual ground speed - it's designed to run the speedometer, odometer, and fuel computer using a calculation based on the stock tire size. Installing larger or smaller diameter tires will slightly affect the speedometer accuracy as well as the fuel computer accuracy, but they will both be inaccurate by the same amount so your manual fuel mileage calculations will still be using the same 'distance traveled' data as the fuel computer.
On most cars the Mass Air Flow sensor (MAF) is used to estimate the fuel consumption.
The MAF measures how much air the engine is using and it knows that for every 14.7 grams of air, one gram of fuel is used.
Not correct. If you've ever driven a vehicle equipped with an air/fuel meter you know that the fuel mixture varies over a wide range depending on driving conditions, and is hardly ever at stoichiometric (14.7). As noted above, the computer knows exactly how long each fuel injector is open and can accurately calculate fuel usage based on that data.
