Preignition warning device

A method of evaluating the operation of a spark plug ignited internal combustion engine including the steps of:

• applying a relatively low voltage across a spark plug associated with at least one engine cylinder;
• monitoring the current flow through said spark plug;
• deriving an initial alarm signal from the monitored current flow whenever the current flow immediately preceding a spark event exceeds a predetermined threshold;
• temporarily enabling both a visible indicator and an audible indicator by said initial alarm signal to inform an operator of the occurrence of current flow associated with said monitored plug which exceeds said predetermined threshold which could damage said engine;
• counting the number of times the current flow through said spark plug exceeds said predetermined threshold level in a predetermined time interval;
• and
• summing said number of times said predetermined threshold level is exceeded in said predetermined time interval to develop a cumulative signal to continuously enable at least said audible indicator when a cumulative number exceeds a predetermined number in a specified length of time to inform an operator of an impending condition that could permanently damage said engine.

A preignition warning system for use in evaluating the operation of a spark plug in engine comprising:

• means for monitoring the current flow through at least one engine spark plug at specified times throughout a number of engine revolutions;
• means for establishing time intervals during which there should be no current flow through the monitored spark plug, said established time intervals being of uniform duration and immediately preceding a spark event for said spark plug corresponding to the rate of the engine revolutions;
• means for monitoring the current flow through said spark plug;
• means for deriving an alarm signal whenever the current flow through said spark plug exceeds a predetermined threshold;
• means for temporarily enabling both a visible indicator and an audible indicator by said alarm signal to inform an operator of the occurrence of current flow through said spark plug in excess of said predetermined threshold which may damage said engine;
• means for counting the number of times said alarm signal occurs in a predetermined time interval;
• means for summing the number of times said alarm signal occurs in said predetermined time interval to create a cumulative signal;
• and
• means responsive to said cumulative signal for continuously enabling at least said audible indicator whenever said cumulative number of alarm signals exceeds a predetermined number during a specified length of time.