System and method for analyzing position data and fuel injector data from a vehicle equipped with a geographical position system (GPS) and fuel injector sensors to enable fuel use patterns of the vehicle to be analyzed. Data defining a flow of fuel through the vehicle's fuel injectors is combined with temporal data and GPS data to produce fuel use encoded GPS data that is transmitted to a remote computer. The fuel use encoded GPS data can be analyzed to determine how much fuel was used by the vehicle during off road use to enable proper fuel tax computations to be performed. The data can also be used to evaluate the mechanical condition of a vehicle. By monitoring fuel use for a trip repeated numerous times, a decrease in fuel efficiency may indicate a mechanical problem (dirty injectors, fouled spark plugs, etc).