Fuel character judging system

The fuel character judging system has an electrical capacitance type sensor which outputs a first detection signal representative of a first character of a fuel mixture. A resistance type sensor outputs a second detection signal representative of a second character of the fuel mixture. A control unit stores first and second maps for a known fuel mixture having known first, second and third numbers corresponding to components of the known fuel mixture. The first map has a plurality of first characteristic lines which respectively correspond to a plurality of values of the first detection signal from the electrical capacitance type sensor. The second characteristic lines are plotted in accordance with the second signal from the resistance type sensor upon changing the known first number. One of the second characteristic lines in the second map is selected in accordance with the first detection signal from the electrical capacitance type sensor. The unknown first number is determined in accordance with the one second characteristic line selected and with the second detection signal for the unknown fuel mixture, from the resistance type sensor. A first characteristic line in the first map is selected in accordance with the determined first unknown number. The unknown second number is determined in accordance with the selected first characteristic line and with the first detection signal for the unknown fuel mixture, from the electrical capacitance type sensor. The unknown third number is determined according to the first and second determined unknown numbers.