Is injector flow rate = Mass fuel flow?
If so then AFR = MAF/Injector flow rate. Can someone please confirm this?
Yes, provided the following conditions are met:
the units for the values MAF and fuel flow values are consistent.
if you're using OBD-II parameters the values are usually in different units. In fact, fuel flow is usually volumetric (L/hr) and not mass flow like the reading from the MAF so you would have to correct for that
by injector flow rate, I'm assuming you're looking at all injectors combined, not just one injector.
the MAF sensor reading is an accurate representation of the actual air flow. Ageing sensors can give false readings. This comment also applies to fuel flow (think clogged injectors, stuck open injectors, etc.)