Hello,
The method that you have proposed has already been tested on the OBD products and the results show that the calculations are not correct for the all cars (for example, in diesel or petrol vehicles with turbocharger we got wrong calculations) and the OBD product does not know which car is connected and can not provide correct calculations. For Petrol and LPG driven vehicles without turbocharger difference from real fuel consuption was about 10-25% (depending on car model and driving style). So we do not recommend using that calculation method, but if you are sure that this method will be suitable for cars that you use, please contact Teltonika sales managers for development of this functionality on FM3001 device.
Regards