Diagnostic system for a capacitor discharge ignition system

An apparatus (8) for monitoring ignition in an engine cylinder, ignition in the engine cylinder being controlled by an ignition system (10) which includes a transformer (22) having primary and secondary coils (26,28), the secondary coil (28) being electrically connected in series with a spark gap (22) in the cylinder, the ignition system (8) further including a selector switch 34 being adapted to receive a cylinder select signal and responsively connect the transformer primary coil (26) to a power source (18) to induce current flow through the primary coil (26), the primary current resulting in a voltage potential across the spark gap (22) which normally increases to a magnitude sufficient to cause a spark across the spark gap (22), comprising:

• current sensing means (62) for sensing a current flowing through the primary coil and responsively producing a primary current signal;
• a monostable multivibrator (14) adapted to receive the primary current signal and produce a stop time signal in response to the primary current signal reaching the preselected threshold;
• timer means (100) for receiving the cylinder select and stop time signals and producing a delay signal in response to a time delay between the reception of the cylinder select and stop time signals;
• and
• diagnostic means (124) for receiving the delay signal and producing a primary to secondary short circuit signal in response to the delay signal being within a first range of values, producing a secondary short circuit signal in response to the delay signal being within a second range of values which exceeds the first range of values, producing a normal ignition signal in response to the delay signal being within a third range of values which exceeds the first and second ranges of values, producing a spark plug maintenance signal in response to the delay signal being within a fourth range of values which exceeds the first, second and third ranges of values, and producing an open circuit signal in response to the delay signal exceeding the first, second, third and fourth ranges of values.

A method for monitoring ignition in an engine cylinder, ignition in the engine cylinder being controlled by an ignition system (10) which includes a transformer (22) having primary and secondary coils (26,28) the secondary coil (28) being electrically connected in series with a spark gap (22) in the cylinder, the ignition system (8) including a selector switch (34) being adapted to receive a cylinder select signal and responsively connect the transformer primary coil (26) to a power source (18) to induce current flow through a the primary coil (26), the current flow through the primary coil (26) resulting in a voltage potential across the spark gap (22) which normally increases to a magnitude sufficient to cause a spark across the spark gap (22), comprising the steps of:

• sensing a current flowing through the primary coil and responsively producing a primary current signal;
• producing a stop time signal when the primary current signal reaches a preselected threshold which is normally sufficient to cause a spark to arc the spark gap (22);
• producing a delay signal in response to a time delay between the production of the cylinder select and stop time signals;
• and
• comparing the delay signal to a plurality of preselected thresholds and responsively producing a status signal indicating the status of ignition in the cylinder.