I am curious, how does a "knock event" change the resistance of a spark plug/wire/coil? What is the Anti-knock system measuring?

*Edit* Never mind, I found an explanation from a delphi engineer on another forum.

 

I don't feel right cutting and pasting info from another site. You can search and find it pretty easy. Anyway, it seems most plugs will function OK in the system, the problem maybe the way the spark plug connector in the wire was designed specifically to make solid contact with the connector on the plug. Apparently, different spark plug brands have very slightly different connectors and that can screw with the connectivity which can mess up the ion sensing. No, I don't fully understand, but I think I get it a little

 

Interesting. Heaven forbid you change your spark plug wires, then there's no *chance* of the H-D Anti-Knock System (TM) functioning properly.

 

I am not sure, all I know is the delphi engineer said it might be a problem and that it was just about impossible to measure the resistance of the system without a special meter because the plug is not a resistor . He indicated the issue is not the resistance of the plug, but more maintaining "perfect continuity" from the coil to the plug tip. Apparently, the tolerance for plug types is fairly large and trouble codes that maybe tripped by this system are more likely to be related to continuity. But, honestly, I had to look up what ion sensing was .

Ah screw it, the info was on a public forum, if someone wants me to take it down they can let me know. This note is suppose to have come from a Delphi engineer in response to someone from another forum. I love it when a complicated explanation like this comes with a resolution of using pliers to modify a connector.


"Regarding the OEM Champion plugs the resistive element that they use is not a resistor; it is a semiconductor suppression element. The effective resistance is specified to be 6k-15k. Furthermore, there is a fairly strong negative temperature coefficient, so the resistance decreases at normal operating temperature. In my experience, I have typically seen it in the range of about 2k-5k when the engine is running.

Note: Because the suppression element is not a resistor, it cannot be reliably measured with a conventional ohmmeter. The resistance of the element must be measured in an apparatus that provides 1000V pulses (per conversation with a Federal Mogul engineer).

You made it clear that this is all the information you wanted. However, if you want some insight into the ion sense system and related trouble codes, you may read on.

With regards to ion sensing, there is absolutely nothing magic about the Champion suppression element. Any trouble codes that you encounter have nothing to do with the resistance of the spark plug. Our circuit is designed so that we can tolerate a very wide range of resistances. We can easily operate with spark plug resistances from zero to 20k.

The ion current that we measure is in the range of 0-50 microamps. To avoid ion sense related trouble codes, you must have perfect continuity from the ignition coil to the spark plug tip. We have trouble codes P1353 and P1356 (front and rear cylinder, respectively) that are detected if we see no ion current under high speed/load conditions (where the ion current should be strongest). These codes will detect an open circuit in the ignition secondary circuit.

Additionally, we have trouble codes P1357 and P1358 (front and rear cylinder, respectively) that are detected if we see excessive noise on the ion signal. The intention of these codes is to detect an intermittent terminal.

We went through a lot of evaluation of spark plug wire terminals in order to select the one that captures the Champion terminal profile the best. Different plugs have different terminal profiles, so I suspect that’s where the issue is. I recommend “adjusting” the plug wire terminal with a pair of pliers. "

 

I know what you mean, its the 'should' that concerns me.

If other plugs provide no advantage (except as something to spend a lot of $ on) then why risk it? Stock plugs work just as well as any other; so if you have access to both I think its fairly sensible to stick with stock.

This whole ion sensing thing has been around sine the 90s. Made possible by electronic/microcomputer controlled ignition systems. Its a bit of a simplification to say the resistance changes in knock events. Seems it actually that more ions (charged atoms) are produced in the gas immediately after ignition when knock happens. The charge of these ions is detected through the plug, the plug leads and the coil and is fed back to the ECU. I really have no idea how sensitive this system will be to change but as we are talking a few mV here I'd guess its going to be somewhat sensitive.

 

I've done quite a bit of reading on this issue, and as best I can tell, the Champion RA8HC is the Harley 6R12, just re-branded and sold for a little more money- if you have some info/facts that contradict this please share it. The post with the info from the Delphi engineer is clear, anti-knock works over a fair spread of resistance, it's the connections and terminal profile that matter most. Changing to non-stock wires or ignition coil could cause problems, as could plugs with different terminal profiles, with the Delphi system; checking DT codes should show if what you are using is working with the anti-knock system or not.