[basjoos]

If you can get your hands on a SuperMID, they show the injector pulsewidth and it is easy to see the pulsewidth shift as it goes into and out of lean burn. Some people have hooked up a voltmeter to the oxygen sensor and watched for the voltage change as it enters and leaves lean burn. Once you know the voltage for lean and non-lean burn it is easy enough to design an LED output that would come on when the voltage was in the lean burn range. For more info go to gassavers.org and search the forum for "lean burn monitor".