A system of one or more computers configured to perform operations or actions by virtue of having software, firmware, hardware, or a combination of them installed on the system that causes the system to perform the actions. The programs can be configured to perform operations, when executed by computer, cause the computer to perform the actions. One general aspect includes a system, a program to initiate an evaporative control engine off natural vacuum test in a vehicle and identify a geolocation where a fuel was obtained for the vehicle. The system then determines an e100 value and an e0 value for a temperature of the fuel and determines a vehicle percentage of ethanol of the fuel using at least the e100 value, the e0 value, a timestamp, and a fuel tank pressure and adjusts at least one engine parameter based upon the percentage of ethanol of the first fuel.