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General Topics/Tech TipsDiscussion on break in periods, rider comfort, seats and pad suggestions. Tech tips as they become available will be posted here.
A member was patient enough to explain that HD plugs have a form of inbuilt ping control that other plugs dont seem to have.
I just put NGK DCPR7E plugs in my 09 RKC this spring and do tend towards some spirited riding when conditions are favourable
the reason I used those plugs is due to searches on the internet for alternatives and not really wanting to go to Harley to get expensive plugs.
shows how little I know as the HD plugs were the same price as the NGK and the parts guy was a pretty awesome dude.
I looked up spark plug resistance testing on the internet and did 4 separate set up and tests just to make sure I was doing them the same.
the resistance (tested at 20K ohms) was 4.44 for the NGK plug and .11 for the HD plug. Pretty large difference I think. I put the HD plugs in and will see if my bike runs differently. Interesting that the resistances are so different.
disclaimer
I am a carpenter using electrical testing devices. NGK DCPR7E plug HD 6R12 plug
Harley Davidson went to Delphi ignition in 2002. With that, it incorporated Ion sensing ignition. What that means, basically is that the ECU senses the Ohms or resistance used within the gap of the spark plug, and measures said resistance.
If that resistance increases above the set parameters, indicating pre-ignition, the ECU will retard timing, until the resistance is back within parameters, in order to stop the pre-ignition, or "pinging".
I believe the ECU will retard timing as much s 4*.
With that, changing spark plugs to anything other than the OEM specific design and configuration, can/will disable the Ion Sensing abilities of the ECU. Change in heat range or spark plug design can increase (or decrease) the Ohms measured.
HD spark plugs are currently manufactured by Champion. I've read of people that have used NGK with good results and no ill effects to the Ion sensing abilities of the ECU.
Buy the OEM plugs. These are the plugs the ignition system was designed around. It’s black magic. Don’t try to outsmart the engineers. There are better places to save a few $.
first of all, resistance has nothing to do with it, ion sense will work with a coat hangar as a lead.
the resistance is for radio frequency control, very necessary for today's computer systems.
ion sense takes place at the coil driver circuit, it is a parallel circuit that only feeds in when the corona forms that allows the current to flow from tip to shell. the computer looks at this circuit and determines what to do since any irregularities like detonation will alter the sense current that flows parallel to the strike current.
not to say that very high resistance does not effect the system but it is a very forgiving system, aka, a large operational window. on industrial systems we used this to monitor plug life among many other parameters.
Spark plug resistance does make a difference to the ion sensing system. I have documented datalogs that show the difference in false knock spark retard When using the NGK plugs, that usually run right around 5,000 ohms where the OEM 6R12 is right around 105 ohms huge difference.. And my datalog showed it on my PV2-B ..
Last edited by 98hotrodfatboy; May 18, 2025 at 02:53 PM.
no on said the resistance does not make a diff, even a coat hangar has resistance. the system is built around resistance, a design parameter. there is a wide berth or operational window. on the industrial systems we monitor that parameter to determine plug life because as plus age the grow in resistance, reason why new plugs can hide more serious issues within the ignition.
truth told, NO engine fires 100%, there will be misfire and partial burns. also, the resistance of the plug and wires are in good order is NOT a hill for the high voltage. that resistance prevents RF radiation, a ringing effect as the field around the wire expands and contracts. that parameter is also useful as it tell the signature of the strike. ideally the signature would be a rise and fall, but not all energy is used in the coil so as the field collapses in the coil it induces a current which is then fed back at a lower intensity until it either disappears or the coil starts charging again. this is a counter EMF which effect the coil charge and if large enough, will heat the coil and could lead to coil failure. of interest, each system has a unique signature so a chevy on an o'scope looks diff than a ford.
where resistance does matter in in the corona, it is here where current flows and the ion sense feeds in a parallel current which the ecm converts to usable data. funny how people will think that plugs are magic. i have had brand new out the box not even start an engine. will nkg and champion have the same signature, hummmm, probably not. the truth is that that data DOES not cause instant change, the ecm uses a law of averages, aka, an operational window and flags when out the box over a time period. a better system holds a tighter line but i do not think hd is all that smart to begin with.
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Spark plug resistance
