The mpg reading should be fine, but it is not simple to add rpm for this injection type. Needs additional hardware/wiring/code.
I would recommend customizing the custom screen to put something more useful in that spot, i.e. before you load it try (to display instant gph):
Code:
change:
void doDisplayCustom(){displayTripCombo('I','M',instantmpg(),'S',instantmph(),'R','P',instantrpm(),'C',current.mpg());}
to:
void doDisplayCustom(){displayTripCombo('I','M',instantmpg(),'S',instantmph(),'G','H',instantgph(),'C',current.mpg());}