Economy = MPG
Efficiency = BSFC Charts.
Brake specific fuel consumption - Wikipedia, the free encyclopedia
While accelerating, you want
efficiency. 75 to 80% throttle if you have electronic fuel injection (most modern vehicles). My opinion is that if you have more than 3 or 4 miles between stops, then do 75-80%. Anything less than that or if you are city driving, then slow acceleration is best. Overall, this will net you the best fuel
economy.
You still want the best fuel economy (MPG). You have to learn and practice some hypermiling techniques.
Example: You should accelerate on the downhills and avoid increasing speed on the uphills - it takes less horsepower and less fuel that way.
Example: use a steady throttle, not steady speed - allow the vehicle to speed up and slow down in hilly areas while maintaining a steady "TPS" or Throttle Position Sensor.
There are always lots of "discussions" about efficiency and economy. If you put a high load on the engine (such as accelerating, getting the load moving up to speed), you want engine efficiency. When you get the load up to speed, you want economy, or the least amount of fuel to keep it moving. Road conditions, weather, wind speed/direction, vehicle/engine health, fuel quality, driving technique, etc all play a part of getting the best economy.
That Scangauge II will teach you lots of stuff. Ecomodder.com folks (and the articles here) will teach you lots of stuff. And you will see where your vehicle nets you the best fuel economy (MPGs) and at what speed and at what RPM. If you can find folks with the same vehicle they can really help you attain the best MPGs. Have fun!