The Metro is a very fuel efficient vehicle with a long history.  It is capable of exceeding the MPG ratings of "todays" hybrids.
The following should be a good starting point:
- VSS Pulses/Mile = 8208
- MicroSec/Gallon = 0500000000
- Pulses/2 revs = 3
- Tank Gal * 1000 = 10300
Yellow Green wire for VSS (Speed) signal
Tapped into Yellow/blue wire at fuel injector
Small MPGuino sitting in front of Metro instrument cluster
In the 1994 Geo Metro, the ECM is actually on the driver side to the left of the steering column (under the dash). It is very difficult to get at, but the correct wire is still the Yellow with Green stripe.