Abstract: An internal combustion engine analyzer is described which permits analysis to be performed by attaching one sensor to the engine circuit. Timing at idle, engine speed, plug firing parade, etc., can be performed with only one sensor connected to the engine. For more extensive testing wherein additional leads are used, for example, at both the primary and secondary of the engine ignition coil, circuitry is provided for automatically triggering from both primary and secondary input signals or either one if only one is present. The analyzer also contains circuitry that enhances its use with both standard and electronic ignition systems. This circuitry rejects the noise generated by ignition systems in the cylinder ignition signals representative of plug firing so as not to mistrigger, or fire more than once for each plug firing.