[Old Tele man]

EPA mandated use of CAN-OBD-II in 2008, before that each manufacturer used different methodologies, Pulse-Width vs. Pulse Amplituide, etc.

That's why it's only recently that 'universal' gauges have become available...which means legacy stuff isn't going to be supported by the new gauges.

FWIW, I have an AutoMeter 9100 ecometer and find it less than satisfactory because basically only the MPG-average display is usable, the other three display modes are too jumpy and fluctuate too much to be usable.