Abstract: An engine analyzer, to analyze a parameter of a spark ignition internal combustion engine, has a separate probe for connection to each spark plug or lead feeding only that spark plug, so that engines in which ignition pulses pass to the plugs only along separate leads, can be analyzed.

Abstract: An engine analyzer, for analyzing ignition voltage or current signals in an engine of the kind in which each spark plug is fed with a succession of pulses, alternate pulses producing real sparks to ignite the petrol/air mixture, the other pulses producing wasted sparks at a point of the engine operating cycle remote from ignition, the analyzer including circuitry to pass the real spark pulse and inhibit passage of the wasted spark pulses.

Abstract: An engine analyzer including a plurality of probes each connectable to one component of a different pair from a plurality of pairs of engine components, each pair comprising a spark plug and a lead connected direct to said spark plug, in which each probe will emit a succession of pulses during use, some or all of the pulses being of either one polarity or of the opposite polarity, wherein the invention comprises means to process said pulses and to emit coincident pulses all of one predetermined polarity, irrespective of the polarity of the pulses from the probe.