Methods and apparatus for detecting short circuited secondary coil

Abstract

Methods and apparatus for detecting low impedance short circuits in a secondary winding circuit of a coil of a distributorless ignition system (DIS) by analyzing spark discharge signals on a primary winding of the ignition coil. In one embodiment, the duration times of the spark discharge signals are compared to a threshold spark duration time, with a low impedance short circuit being indicated if the threshold spark duration time is exceeded. In another embodiment, two or more spark dwell signals are applied to the primary of the ignition coil for each spark event of each associated pair of engine cylinders. A first or base time period is determined for the first dwell signal by measuring the time it takes the first dwell signal to produce a preselected current flow in the primary winding. A second time period is then determined by measuring the time it takes the second dwell signal to produce the same preselected current flow in the primary winding. The second time period is then compared to the first time period to determine whether a short circuit exists in the secondary winding circuit. A guard-band time period is subtracted from the first time period to define a minimum duration time for the second time period. If the second time period is equal to or exceeds the minimum duration time, a normal secondary winding circuit is indicated. If the second time period is less than the minimum duration time, a short circuited secondary winding circuit is indicated.