Abstract: A motor vehicle fuel composition sensor is responsive to a dielectric constant of a mixture of two fuels such as gasoline and methanol to indicate the relative concentrations of each. The sensor is fuel temperature dependent at high concentrations of methanol; and a fuel temperature sensor thus provides a fuel temperature signal for fuel composition signal correction. Diagnostic apparatus stores references defining permissible operating ranges for the fuel temperature and fuel composition sensor outputs and compares the sensor outputs with these ranges to detect abnormal sensor operation. The reference defining the end of the fuel composition sensor range at maximum methanol, however, is corrected for fuel temperature if the fuel temperature sensor output is within range. An out of range signal from either sensor causes a default value to be substituted for fuel composition.

Abstract: Selective compensation for reductions in fueling capacity normally associated with extreme fuel vaporization rates in the fuel delivery means of vehicle engines, by improved estimation of the conditions normally precedent to such extreme fuel vaporization rates.