You have "unreasonable expectations" that cannot be blamed on the car. If you want to verify the fuel mileage is as it should be, you are going to have to drive it at highway speed for a considerable distance. By staying in the city, every minute you spend idling at a red light gets you 0 miles per gallon. Every minute spent in first or second gear gets you perhaps five miles per gallon, if you are lucky. You are quite fortunate if you can squeak out 13 mpg with that type of driving.
To verify this, you can have your mechanic connect a scanner to view the "fuel trim" numbers. Short-term fuel trims, (STFT) refer to how much more or less fuel the Engine Computer wants relative to the pre-programmed amounts from the factory. The engineers wrote the software for every conceivable variable such as intake air temperature, road speed, engine speed, engine load, coolant temperature, etc, and dozens more variables, but that is just the starting point. Once the engine is running, the computer watches the readings from the front oxygen sensors, then fine tunes the fuel metering calculations as necessary to achieve a perfect mixture. Those slight adjustments are what's taking place right now, as you drive, and are called the "short-term fuel trim" adjustments. If you see on the scanner the current number is, ... Oh, ... Lets say "+1", it means the computer is requesting one percent more fuel under these conditions than what the original software calls for. Typically the computer can adjust the mixture by plus or minus ten percent, and it does that constantly as you are driving.
The scanner will also show "long-term fuel trim", (LTFT) numbers. When it sees it is constantly subtracting fuel for the short-term from what was pre-programmed in at the factory, it moves those numbers to the long-term memory, then, from then on it is these new, updated numbers it starts running on each drive cycle. That way it starts out close to perfect and does not have to make as many corrections to the short-term numbers. This is where you can get an idea of how the computer is managing your fuel mileage. Any numbers close to "0" means not much correction has been needed. If you see numbers real high, plus or minus, it means the computer has been correcting for some variable. Typical things are high or low fuel pressure, a vacuum leak, a misfiring spark plug, and things like that.
I just started driving a smashed/rebuilt 2014 Dodge truck with all the electronic stuff, including multiple fuel mileage readouts. These have made me more conscientious about how I drive, and I have learned a few things. In city driving, I get anywhere between 9 and 20 miles per gallon, and the average is usually around 15 mpg. Once I get on the highway, it is easy to stay around 28 mpg, and the average slowly goes up to around 24 mpg. Even when pulling a trailer, I can keep it at 20 if I am careful, but if I drive like normal without paying attention to fuel mileage, it drops to 15 mpg with that trailer. The main point of interest is how very much lower the fuel mileage is in the city. My average will drop to 16 mpg very quickly once I start driving in the city, then it takes a good 80 to 100 miles of highway driving to get it back up to around 24 mpg.
Also, be aware that on all 1996 and newer cars and light trucks, among the more than 2,000 potential defects that can be detected by the Engine Computer, about half of those refer to something that could adversely affect emissions. Those are the defects that turn on the Check Engine light, and that increased emissions includes problems resulting in burning too much fuel. To say that a different way, if the fuel management system sees you are using more gas than is appropriate, your Check Engine light would be on.
The only other thing you can consider is a dragging brake, but I do not think that applies here. To check for that, stop on a slight incline, shift to "neutral", release the brakes, then see if the car creeps downhill on its own. If it does, the brakes are not sticking.
Sunday, May 27th, 2018 AT 7:24 PM