# Calculating AFR using injector flow rate and mass air flow

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.)

• Yes, I am also getting the AFR matching to 14.7 both by calculation and from OBD – Soumya Sen Jan 17 '16 at 11:01
• @SoumyaSen could you show your calculation in the question? – Zaid Jan 17 '16 at 11:29
• I am getting MAF from MAF sensor. Injector flow = (HP (instantaneous)*BSFC)/(No. of injectors*Duty cycle), where BSFC = 045, No of injectors = 4, Duty cycle = 0.85. I am calculating HP from OBD parameters. AFR = MAF/Injector flow, which comes as 14.703. Car is Petrol driven – Soumya Sen Jan 17 '16 at 12:17