MyE28.com

First of all, my MPG gauge is broken, but I was just curious if there is any correlation...

I have a +20psi turbo gauge with 30mmhg vacuum.

When i'm cruising on the highway on cruise control on level ground, i'm running exactly 15mmhg. When i go up a slight hill, it moves up to 13, 12, 10, all the way to atmospheric sometimes. When i'm going down a hill, The opposite happens. It goes all the way to 20mmhg, 25mmgh..etc

Is there any correlation between vacuum pressure in the manifold and miles per gallon?

Basically, the deeper the vacuum, the less fuel you'll use.

This should be pretty easy to do with a microcontroller (or MS). Use your tire size and diff signal to calculate speed and the injector pulse width to determine your fuel consumption, calculate and have an analog output to an analog volt meter that you label appropriately.

edit: Hell, if you really get creative you can determine what voltages the stock mpg meter wants and output it there.

Sounds interesting, thanks for the help!