The "economy" vacuum gauge would always read red for me, and I do pretty well with my strategies. Energy spent creating a vacuum is wasted energy.
If you have a pre-OBDII vehicle and are very handy, try one of the ideas for combining easily-measured fuel injector duty cycle with vehicle speed info. If you're not so handy, you may be able to retrofit an OEM fuel economy unit from a similar model; it has been
done with an Acura unit in a Honda, for example. Otherwise, if you're willing to settle for relative fuel rate (but not MPG), you can just use a duty cycle meter to monitor your fuel injectors; see the link in my sig for a DIY fuel rate meter where I have instructions for that as well as links to all the other ideas in this paragraph.
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