Since 2001, H-D has been using the Delphi Ion-Sense knock and combustion sensing sytem. This system uses the secondary ignition system to monitor each cylinder for combustion and for detonation, and any significant change to the electrical characteristics of the component parts (coils, plugs, and wires) can in fact create false data, poor performance, and error codes. Of course, H-D always tells us to use only original equipment replacement parts even when there is no valid reason (like oils). In this instance, however, there really is a valid reason to stick with O.E. parts.
Jerry
From Delphi literature:
Ion Sense Ignition System – The Delphi ion sense ignition system uses a conventional spark plug as an "in cylinder" sensor for combustion sense/control. This technology is in production on both automotive and motorcycle applications. Production [highlight]functions of the ion sense system include misfire detection, cylinder identification, and individual cylinder knock detection and control[/highlight]. Future functions include fueling compensation for high driveability index fuels. All Delphi coil per cylinder ignition coils can be configured as an ion sense system.