Some Theory on Ion Knock Sub-System

Discussion in 'Electrical' started by Hoople, Jul 7, 2010.

  1. Hoople

    Hoople Account Removed

    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.:p 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.
  2. ultrat

    ultrat Senior Member Contributor

    I'M curious to tx. hoople..
  3. mnultra

    mnultra Active Member

    Good grief Hoop. Like I didn't feel dumb enough already :shock
  4. glider

    glider Veteran Member


    Great post but could you elaborate on this part...:s

    and CH+C2H2=> C2H2*+c*
  5. HDDon

    HDDon Experienced Member Contributor Retired Moderators

    I don't doubt your theory explanation, but I do wonder how broad is the ion sensing? If you were to introduce any variable to the equation does the anti knock firmware have enough parameter to adjust to the difference? If you were to introduce a different fuel mixture or hotter spark does this throw the electronic timeing off? This seems like a convoluted method to determine detonation, but then I'm not really sure that any other method would be any better. Now where is my morris magneto? Thanks Hoople
  6. RetiredJake

    RetiredJake Junior Member

    I asked, you provided. Now if I only understood it. :bigsmiley20:

  7. Hoople

    Hoople Account Removed

    My guess is the (3) carbon & (3) hydrogen atoms get converted into a compound made up (2) ion Hydrogen atoms, along with (2) carbon atoms and (1) carbon atom that either has 1 extra electron or 1 missing electron.

    I really don't know but I do have a friend that may be able to explain it better if you want me to ask him.

    BUBBIE Well-Known Member

    I liked the report But also like the word UN-plug.... I could never figure where, TOO many plugs, So I'll just have to live with "what it does".. Thanks for the report.... I liked my Hammer on the intake better, easier for me to understand.

  9. Hoople

    Hoople Account Removed

    (It's not my theory because I just copied it) My exact point. What I got out of the article was the ECM firmware must match a given set of engine parameters.
    My guess would be once you change an important part of the engine (heads, compression ratio, type of fuel,) you have to modify the firmware to now read those new set of parameters.

    Remember that Delphi would not answer my questions. I came up with this info on my own and this is how I understand how the subsystem works. By no means is it Gospel or an absolute truth.

    But I just can not see 1 set of software instructions fitting every possible application or engine. They must be based on a particular engine.
    But who knows, maybe I am wrong. But I sure would be surprised if I was.
  10. glider

    glider Veteran Member


    Not necessary Hoop but I would be interested in the neutrons and their part in the equation :D