Originally Posted by IH84DZ
I see a lot of variables in here that don't make your mileage figures a shocker. Unless you are calculating fuel economy by filling your tank, logging mileage and filling the tank at the same pump again while dividing the miles driven by gallons used - your fuel usage figures are terribly inaccurate. This may sound unacceptable given you are using the fuel gauge but if you understood how a fuel gauge worked it would make more sense. They are accurate estimations of fuel level, not accurate measurents of fuel level.
A drive of less than 3 miles (especially in cool temps) is likely not enough time for the engine to reach closed loop. In open loop it fuels the engine based on a programmed table that is certainly rich of stoich and thus it will consume more fuel in open loop than it will in closed loop. This is aside from all the other problems you can expect with such a short run cycle.
Your tire compound will negatively affect fuel economy as well because they have more drag compared to a street tire - regardless of how much air you put in them
It is a good idea to check for dragging brakes - especially if you've had brake issues in the past
How much extra weight is in the car?
What is the ethanol content of the fuel being used?
Your woman may have poor driving habits. I can make a motorcycle get 10mpg if I try hard enough........
Get rid of the K&N filter. MAF based Fords are notorious for aftermarket filters (especially "performance" filters that use oil to trap FOD) messing with the air turbulence across the MAF sensor and/or contaminating the sensor with oil. Comparing what mileage you get with a go-fast air filter to what others get with paper filters isn't a very valid comparison.
0 extra weight in the car - back seats and trunk are EMPTY.
Regarding the short trip to work - should I let the car warm up? And for the record, I drive my Mazda Miata about the same mileage to the health club every other day and that is IT (I work from home). And I STILL GET 24-25 MPG! What the hell gives here with the Focus!? And the Miata is older - 1997!
You've summarized things well and I will take your advice tonight and get a new air filter, and sell the stupid K&N. I've been wondering if I simply drank the kool-aid on that one without thinking it through/researching.
The gasoline I purchase is local Mobil or BP - so whatever their standard is for ethanol content?