The ion knock detection is really MODEL based !!
I wrote a little on the Harely tech talk board a few years ago. ( Probably due to the same confusion )
From: fatboyrr
Sent: 9/12/2003 9:24 PM
Here goes, I'll make it the condensed version. First ION knock detection is the direction most applications are going to use. The old PEZIO sensor relied on a vibration ( caused by some level of knock ) to register at the sensor, It is very hard to detect low levels of knock and seperate the singal ( knock from detonation ) from normal engine vibrations, such as valve closings on a Harley engine. On most vehicle applications the knock sensor can sense true knock from noise, but may not READ every cylinder in a multi-cylinder engine at every cylinder at every RPM, But most system use a GLOBAL retard scheme where any knock will retard spark to all cylinders at the same amount. New systems are going to indidvidaul cylinder knock detection where only the cylinder producing knock is retarded and only until knock ( detonation stops) so in a V8 or V6 you might only have one or two cylinders with any amount of retard.
The advantage of the ION system is it is not dependant on a sensor location and it can be calibrated to detect each cyclinder at all engine speeds and loads.
ION sensing knock detection does not use a Sensor that is externally mounted on the engine. The name ION sensing is derived from the fact that as detonation happens IONIZATION at the plug tip changes the resistence to fire the plug. The actual detection to this change in resistance is internal to the coil and the signal is sent back to the ECM. Software tables are then calibrated using model based software. The way it is calibrated is important to understand WHY some folks are having TROUBLE. A very sophisticated Combustion measurement system is placed on a development engine and actual cylinder pressures are recorded vs. crank angle degrees and coil operating ranges, as the engine is running at set speed and loads. By reading "NORMAL" outputs from the ignition module electronics to the ECM input and noting the change when detonation casues Peak cylinder pressures to rise, a model can be developed that as long as the signal from the ignition module is outputing the "expected NORMAL" signal back to the ECM no retard will occur. A change in resistence value and amount can be correlated to a given rise in pressure in the chamber during combustion. Detonation causes very large spikes in pressure even at very low levels of detonation, so the model can and does detect even before "audilble" detonation ( that which can be heard ) happens. It is a very good system and very reliable with one HUGE exception. Detection is dependant on the values calibrated in the software that represent knock, and are based on a stock engine ( or a known modified engine such as the STAGE I,II etc.) with a GIVEN set of Production intent parts.ie , Spark plugs, wires, and even compression ratio can and does change the resistance at the coil. So once folks start changing wires, Plugs ( to non-factory specs) and modifing the engine cams, compression ratio etc,( and even expected A/F ratios, and therefore combustion temperature) the values derived form a production engine are no longer valid and may cause the software to "determine" that knock is present when it's not or fail to dectect knock when it should.
So Harley knock detection is really not that different than other vehicle manufactures, it's US the users that may not understand the impact on a calibrated system when making major or even minor changes. The STAGE flashes are calibrated to work correctly ONLY with very specific parts. One open exhaust or aircleaner is not the same as another of a different brand.... THE LEARNING CURVE will be steep and there is alot of mis-information floating around.....
Added Today:7-10-07
PLUGS are PART OF THE system. You may not notice if the system is working or not as low levels of detonation are not audible, but can and do cause issues over a longer period of time. Additionally, even LOW LEVELS of detonation in high compression engines can lead to "PRE-Ignition " from hot spots caused from this low level of detonation. Pre-ignition is far more damaging than detonation, as that ( pre-ignition ) is mainly the cause of "HOLED PISTONS".
Just a word of caution !!!
And just because SOMEONE else may have used a different PLUG without issues, does not mean it will work for everyone else. Where, and at what operating range of the engine along with the fuel, are just some of the variables that might allow one to work and one NOT TO work correctly. And one failure of the KNOCK system at precisely the wrong time can have very dire results.
Manufacturer's not only test as many variables as possible, when calibrating an engine, but build in a margin of robustness. And one last point about using OTHERS experience as a basis for no BAD RESULTS. Do you think there are NOT changes to both software and calibrations as standards CHANGE from year to year? Those darned engineers need something to do !!!!
Personally, I see no reason to use anything other than stock plugs. They work and they were calibrated for our engines.
