Misfire-detecting system for an internal combustion engine which detects a misfire due to the fuel supply system

A misfire-detecting system for detecting a misfire occurring in an internal combustion engine having an ignition system including at least one spark plug, engine operating condition-detecting means for detecting values of operating parameters of said engine, signal-generating means for determining ignition timing of said engine, based upon the detected values of said operating parameters of said engine and for generating an ignition command signal indicative of the determined ignition timing, and igniting means responsive to said ignition command signal for generating sparking voltage for discharging said at least one spark plug,

• said misfire-detecting system comprising:
• voltage value-detecting means for detecting a value of said sparking voltage generated by said ignition means after generation of said ignition command signal;
• and
• misfire-determining means for determining a duration of a discharge of said at least one spark plug, based upon an output form said voltage value-detecting means, and for determining whether or not a misfire has occurred in said engine, based upon the determined duration of said discharge, wherein said misfire-determining means includes
• measuring means for measuring said duration of said discharge form a time of generation of said ignition command signal, based upon said output from said voltage value-detecting means, said measuring means for determining a reference voltage value based upon said output form said voltage value-detecting means whenever said ignition command signal is generated, for measuring a time period during which said sparking voltage subsequently detected by said voltage value-detecting means is continuously greater than the determined reference voltage value, and for adopting a measured time period as said duration of said discharge, and
• comparator means for comparing the measured duration of said discharge with a predetermined time period,
• wherein said misfire-determining means determines that a misfire has occurred in said engine, when the measured duration of said discharge is shorter than said predetermined time period, as a result of said comparison by said comparator means.