Fuel supply misfire-detecting system for internal combustion engines

In 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 values of operating parameters of said engine detected by said engine operating condition-detecting means and generating an ignition command signal indicative of said determined ignition timing, and sparking voltage-generating means responsive to said ignition command signal for generating sparking voltage for discharging said at least one spark plug, and voltage value-detecting means for detecting a value of said sparking voltage generated by said sparking voltage-generating means after generation of said ignition command signal, the improvement comprising:

• differentiating means, connected to said voltage value-detecting means, for differentiating a value of said sparking voltage detected by said voltage value-detecting means;
• misfire-determining means, connected to said differentiating means, for comparing a differential value of said sparking voltage obtained by said differentiating means with a predetermined value, and for determining, based upon a result of said comparison, whether a misfire has occurred in said engine;
• and
• time period-limiting means, inserted into a path from said voltage value-detecting means to said misfire-determining means and connected to said signal generating means, for setting a comparison period of time upon which said comparison, of said differential value of said sparking voltage with said predetermined value, is to be made, and wherein said misfire-determining means compares said differential value of said sparking voltage with said predetermined value to determine occurrence of a misfire solely during said comparison period of time set by said time period-setting means.