There was 1 member out of 25,000 that wanted to know more about the Ion sensing knock retard sub-system so here it is. The Theory of operation on the Ion-Sensing Spark advance control, is interesting and what I found does seem to be at least believable to me. This technology has actually been around a while and seems to have been developed in the mid to late 1990's. The more I read about it, the more I wonder how it works at all with any repeatable accuracy. But, despite how I feel, it does seem to perform very well.(or at least from what I have witnessed on my bike which is a Factory Stock Bike) To start with, Ions are produced when an atom gains or losses one or more of its electrons. During combustion the molecular change of different fuels produce Ions. Some of the Ions that are produced are: CH+O=> CHO*+c* ,,,, CHO*+H2O => H2O*+CO ,, and CH+C2H2=> C2H2*+c* The * is the atom who has now become an Ion and is - or + an electron. The AMOUNT of ions produced depends on the peak pressure point (PPP) that is created within the cylinder during a combustion event. During Detonation, peak pressures sky rocket and more Ions are produced. Therefore if we can read the amount of ions produced we can determine if the cylinder is in a state of detonation. So in order to detect or read the amount of Ions, a DC bias (voltage) is applied to the spark plug which will generate an electrical field which make the Ions move and generate an "Ion Current". This DC bias voltage is applied to the spark plug gap right AFTER the combustion event takes place. Right AFTER the combustion process, the Ions are produced, hence the need to apply the bias voltage right after the combustion event. The coil pack has an additional wire to transmit this current information to the ECM. The sensed current depends on the Ions that are created. The interesting part is that the sub-system current reading is dependent on engine temp, humidity, concentration of fuel (A/F ratio) and type of fuel used (gas,E10% etc). Therefore the information that is sent to the ECM is very rich in data but also very complex to analyze. I see the firmware used in the ECM to analyze this information as being the "key" to the entire subsystem working as planned. The white pages I found go into depth about how this current or "ringing voltage" is understood. After reading it several times it seems to me that the secondary resistance of the coil, plug and wire would be very important and should remain at a constant value in order for the software to interpret the information. (but for some reason the HD6R12 plugs are not what I would call a "constant" so you got me on this part) Another thing that hits me "head on" is this. If you make any changes that will result in different combustion pressures (pistons, compression ratio, more heat, different fuel etc) I would guess you must modify the ECM detection software. I would bet if you change the compression psi to a higher number, the system may see that as detonation when it really was not. The system threshold would have to be lifted. But since that can not be done,, on a performance bike I would disable the system completely and dyno tune the correct spark advance map by hand. This is how I see this entire subsystem: I do wonder how much E10 fuel effects the amount of Ions produced. On a completely stock bike, I would just let the system do it's thing. It is great insurance against detonation. But if I truly had a performance street machine, or if I wanted to extract every ft pound of torque I can out of the engine, I would disable it and hand write the spark advance maps using a dyno, some common sense and my ears. I wonder if when a dyno tune is performed, they look for the subsystem kicking back the timing. There just may be more HP in that pull that is being masked by false timing retard values.