spark plugs
Seasoned HDF Member
Joined: Mar 2010
Posts: 20,850
Likes: 7,391
From: Poolville
The problem with running after market plugs is that the ION sensing knock control goes out of whack with the higher radiance plugs..OEM plugs are right around 105 ohms and NGK are typically 5000 ohms generating more false knocks and retarding the ignition timing. So your losing power.. Factory setting for knock retard is typically 6° but can be set to any number with a tuner..
Last edited by 98hotrodfatboy; Mar 16, 2026 at 08:47 PM.
Tourer
Joined: Dec 2022
Posts: 264
Likes: 201
From: Canada
The problem with running after market plugs is that the ION sensing knock control goes out of whack with the higher radiance plugs..OEM plugs are right around 105 ohms and NGK are typically 5000 ohms generating more false knocks and retarding the ignition timing. So your losing power.. Factory setting for knock retard are up to a max of 6°..
Club Member
Joined: Apr 2016
Posts: 11,358
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From: Inland NW
He is speaking about the Twin Cam for the OPs reference. Your '22 will run aftermarket plugs just fine, without issue.
Cruiser
Joined: Nov 2025
Posts: 101
Likes: 81
From: Slovenia
The problem with running after market plugs is that the ION sensing knock control goes out of whack with the higher radiance plugs..OEM plugs are right around 105 ohms and NGK are typically 5000 ohms generating more false knocks and retarding the ignition timing. So your losing power.. Factory setting for knock retard is typically 6° but can be set to any number with a tuner..
Here is the answer from another forum, where a member asked directly a delphy engeneer...
"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. "
Last edited by JuzySoftail; Mar 17, 2026 at 01:33 AM.
Seasoned HDF Member
Joined: Mar 2010
Posts: 20,850
Likes: 7,391
From: Poolville
Well that is not completly true, OEM plugs are specified for resistance 5-15kOhm and NGKs are also around 5kOhm so there shouldn't be a problem. Some tuners were complaining about iridium plugs which are different but standard NGK plugs works the same as OEM regading knock sensing.
Here is the answer from another forum, where a member asked directly a delphy engeneer...
"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. "
Here is the answer from another forum, where a member asked directly a delphy engeneer...
"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. "
Seasoned HDF Member
Joined: Nov 2006
Posts: 5,832
Likes: 1,870
From: East Coast, USA
I've been using Autolite #4164 spark plugs in my 2011 Twin Cam. Cheap and available at my local Walmart, It even has a resistor value of 5k ohms. But why would Autolight use an 11/16" hex size? I use a deep socket to remove the plug, but I've yet to see an actual 11/16" spark plug socket.
Cruiser
Joined: Nov 2025
Posts: 101
Likes: 81
From: Slovenia
get your meter out and check the difference of the 2 different plugs.. You will see a massive difference in actual core resistance and when using the NGK's I data logged constant knock retard events.. Hard evidence.. When I reinstalled the OEM's, it all went away.. that's my proof and not just someone's explanation.. There's always a difference between theory and facts.. I got the facts...
Which NGK's were you using, classic dcpr7ea or iridium?
it's a bit strange to me that the whole system would be built around one specific spark plug which was around I belive before the system itself so it is probably nothing special...
I'm not claiming I'm right, don't missuderstand me, it is just way to strange for me, that the system would work with only one specific spark plug...