Abstract: An internal combustion engine is equipped with a plurality of cam sensors that output cylinder discrimination signals during every uneven crank angle interval, and specific cylinders are discriminated based on said cylinder discrimination signals output from said plurality of cam sensors. Based on the discrimination result of said specific cylinder and said cylinder discrimination signals from cam sensors, the cylinders other than said specific cylinders are discriminated.

Abstract: An instrument of the type employed to measure the conduction angle of the ignition coil of the battery-powered ignition system of an internal combustion engine comprises input connectors which are connected to terminals of such ignition system and an evaluating circuit which generates a signal corresponding to the conduction angle to be measured by ascertaining whether an input signal derived from the input connectors rises above or falls below a predetermined threshold voltage level. For differing types of conventional ignition systems, differing threshold voltage levels are required, but instead of resorting to manual switchover to such different levels, the instrument of the invention modifies the threshold voltage level employed in automatic dependence upon the value of the input signal derived by the input connectors. The threshold voltage level assumes a first value when coil conduction ceases and a second value when coil conduction recommences.

Abstract: To permit tests of: ignition timing; dwell angle; engine speed; and voltage levels, a pulse train is provided derived from the ignition system of the engine; the pulse train is applied to a frequency multiplier, preferably a phase locked loop (PLL) which provides a sequence of output pulses having a pulse repetition rate which is a multiple of the frequency of the signals or pulses of the pulse train. An AND gate has the multiplied signals applied thereto and is enabled, selectively, in accordance with the desired test. The output of the AND gate is applied to a counter which counts multiplied pulses within the interval of enabling of the AND gate, the output being applied to a digital indicator to provide a direct readable digital output; preferably, the multiplication rate is selected to provide a digital output indication which is directly readable in desired units.

Abstract: A circuit for measuring the dwell angle of an engine ignition system having contact points which close to conduct current through a coil, i.e., dwell, and which open to generate an ignition signal. The primary ignition signal is monitored and shaped to form an output voltage level for comparison against a reference voltage level of a selected percentage of car battery voltage. During the time of dwell, the ignition signal's output voltage level is less than the reference voltage level causing a voltage comparator circuit to direct a relatively constant and independent current to a meter for visual display of the dwell time in terms of dwell angle. The extent of dwell angle displayed is determined by the ratio of the time period over which current is delivered to the metering circuit to the total time between spark plug firings, properly calibrated for the type of engine being tested.