the ignition will fire when turned on and off, which is a GOOD way to test the sensor..The tester fires the ignition without the sensor, but does not directly test the sensor....The sensor is bad if the ignition fires when turned on and off, but not when the crank is rotated...There is no way a sensor will be intermittent unless one of the wires is loose..Either it works or it doesn't...this only applies to U S made ignitions, the others need rpm to fire....Syncro spark modules have no effect on this, except that a syncro spark equipped ignition will fire more than once when the crank is rotated back and forth....