Spark plug voltage probe device for use in an internal combustion engine

A spark plug voltage probe device which detects a voltage applied to a spark plug installed in an internal combustion engine so as to analyze a burning condition in the internal combustion engine on the basis of the voltage applied to the spark plug, the spark plug voltage probe device comprising:

• a rubber collar (74) surrounding a rubber cap (7) secured to a high tension terminal (71a) of the spark plug (71) so as to form a static capacity between the high tension terminal (71a) and the rubber collar (74);
• an electrical conductor (73) provided between the rubber cap (7) and the rubber collar (74), said conductor (73) being electrically connected to a microcomputer by way of an input cable (64) so as to analyze a spark plug voltage waveform;
• a condenser (42) connected at one end to ground while connected at the other end to a common point (A) between the electrical conductor (73) and the microcomputer so as to reduce the spark plug voltage according to a capacity of the condenser (42);
• a resistor (43) connected in parallel with the condenser (42) to provide a time constant;
• and
• said microcomputer recognizing a normal ignition represented by a single short pulse derived from the waveform of said spark plug voltage, and recognizing an ignition failure represented by a simultaneous single short pulse and wider pulse derived from the waveform of said spark plug voltage.