[Phantom]

I keep hearing that this and that cannot be reported by the OBD port that I do not believe like AFR and EGR. I do not know if those are just not a standard and each manufacturer uses a different command it poll them but I know that my scanner/tuner can read both along with several other things.

If you can have the PCM reprogrammed the OBC can then be calibrated. How to do this is take the Liters used reads 16L and the actual is 15L you are 1L off. So 1L/15L=6.7% you will need to have the Injector Flow Rate (IFR) adjusted.

IFR is measured in time to flow 1 gram of fuel. So the smaller the number the less amount of time the car thinks is needed to flow 1 gram (more flow). The car is currently thinking more fuel is flowing, so we'll raise the IFR numbers by 6.7%. Note that all the fuel trims will suddenly be off by about that 6.7%, unless we also lower the MAF table by that same 6.7%.

I did that on my car and its allot closer to actual MPG.
If you can't have your cars PCM, ECU, VCM or what ever they refer to the cars computer as reprogrammed sorry to get your hopes up but it could help someone.