free website stats program Stock 6R12 Plugs | Page 2 | Harley Davidson Forums

Stock 6R12 Plugs

wilks3 said:
Thats all true, but, my Ion sensing gizzmo is hooked up. So why would plugs that HD sells and recommends work in some bikes and not others?
It just doesn't make sense and there's got to be a reason.
Still confused....
wilks3
:USA
Click to expand...

Nothing to be confused about, The ION sensing works on resistance in the secondary ignition circuit and if you change the resistance with a different plug there's a good possibility that the system will not work or work properly. From the way I understand it Harley has the plugs specked for their engine with a specific heat range to accommodate the engine which in turn is for it's ION sensing as well. Don't put too much stock in what they tell you at the dealers unless you KNOW that they know what they are talking about.

Maybe this will give you a little more understanding how the ION system works...

Harley Davidson Community
 
But aren't the 6R12G, 6R12PP, and all the Screamin Eagle plugs spec'd for Harley?
Surely they would be, and thats coming from HD Milwaukee not the local HD shop.
I've read posts here and other forums, but nobody can explain why the "better" HD plugs, not other brand of spark plug, sometimes work ok and sometimes not. I understand how the Ion system in theory works, and thats what makes all the different ohm values of HD plugs not seem right.
wilks3
:USA
 
Last edited:
Don't have an answer for you there but perhaps the other plugs are not made by the same manufacturer?

The resistance in the high priced plugs from Harley is different than the stock plugs. Anybodies guess there.

Champion makes the HD plugs, I don't know who makes the others.
 
I called HD tech service and this was their reply

According to one of our engineers, all H-D spark plugs are compatible with the Ion Sensing System. The high resistance of spark plugs requires a special tool to properly measure their resistance value. A typical multi-meter that uses a 9 volt battery will not give an accurate measurement.

The Ion Sensing circuit uses the secondary of the coil, the plug wires and plugs to complete the circuit. For the circuit to operate properly the plug wire connections at the coil and the spark plug must be clean and tight. We do not recommend aftermarket spark plugs or spark plug wires for this reason. If the resistance were too high or open a Digital Tech Code would set.

As for spark knock, the system monitors fromt and rear cylinders independently. The Ion Sensing circuit is monitored by the ECM under load an high speed conditions. It is used to determine combustion quality and is not used during start event. Because of the many variables in engine tolerances such as compression, injector flow rate, motor work, exhaust, etc. We cannot comment on why one set of spark plugs may show improved starting over another set.

I hope this information is helpful to you.

Hoople, Did you know about this special tool to measure spark plug resistance?
This doesn't really explain to me my starting problem with the "gold" plugs, but at least I got a reasonable answer.

Thought I would pass on to you guys/gals.
wilks3
:USA
 
wilks3 said:
Did you know about this special tool to measure spark plug resistance?
Click to expand...

I am not sure but I think they are referring to a "Megger". In my opinion I would not expect to hear a real good understanding of how the ION subsystem works out of the Moco. It is not their job to understand or to know exactly how it works. Delphi did not developed the system just for Harley. It was around long before Harley started to use it on their bikes. Harley wanted spark knock retard in their bikes that was firmware driven (to push the envelope for emissions and fuel economy) and Delphi already had the package as part of the ECM.

Last year I tried to contact Delphi about it but the division responsible for the Ion subsystem is located in Germany. I wrote to them but received only lip service.

So much of the spark plug resistance theory just does not make any sense to me. In the beginning I would have thought that changing the cranking/running PSI compression would require different firmware in the ECM due to a different threshold in the creation of ION's but I found out later that was not true. The system does see detonation at the proper threshold regardless of the fuel used (somewhat amazing), and regardless of the combustion pressure.
So it seems that the ION's produced during detonation have a "certain resistance" regardless of any other variable.

You can unscrew the top of a 6R12 and the pressure spring along with the "resistor" will fall right out. Well it turns out this "resistor" is really a thermistor which really makes no sense to me at all and is nothing like you would see with any other spark plug. If you change just the temperature of this "pill", you will see it's resistance changes from 33K to something like 2K ohms. That is broad range beyond what I would have expected to see.
I would think if the resistance was so critical, this spread would be unacceptable.

I really don't know what the bottom line is on this topic.
 
Hoople, We used a Megger in the coal mines to see if a cable's internal insulation was damaged if it got run over, pinched etc. It would put high voltage, low amperage to test the cable.
I was surprised I got that much of a response from HD. They were nice though!!!
I, like you still don't get it with the spark plug resistance all over the place. Oh well.
It starts, runs, doesn't make any unusual noises for a HD and still gets over 50mpg. :D
HD 6R12's are it, period, from now on.
wilks3
:USA
 
I'd been doing a lot of reading all over the web about the Delphi system and the 6r12 plugs and thought it strange that a change in spark plug could cause that much trouble so I had to see for myself.

Granted a standard volt/ohm meter won't be accurate but that's about the only thing most of us have hanging around that can measure resistance, accuracy is not that important for this particular test. On a normal spark plug ( I used an Iridium ) when you measure the resistance the meter will steady at around 5 K, which has been the standard resistance ever since they started using resistors in spark plugs.

When you do the same test on a 6r12 plug, depending on the spark plugs temperature, it will start out at say 18 and then slowly start counting down. My guess is that it is because the plug is warming up. I've never held the meter probes on the plug long enough to see where it would eventually stop but it is odd to watch the resistance changing.

My understanding that on a stock bike with the stock download and computer set up the ECM is looking for this reading from the plug to determine pre ignition or the status of combustion in the cylinder. Then based on a set standard of paremeters loaded into the ECM it adjusts the timing as required for the engine to eliminate knock/pinging.

My guess is that when you use a plug other than the 6r12 the system will still work ( bike will start, run accelerate etc ) but it will only vary the timing based on a 5 k reading which will not work properly at all loads on the engine as the ECM only sees the one reading, so it sets the timing etc based on this value.

When I run an Iridum plug in my stock 08 Softail the bike starts better and idles just a little bit faster than with the 6r12 plug. The plug colour is lighter when using the Iridum verses the 6r12 plug. The effects are the same as one would get if you adanced the timing on a standard engine of days gone by.

Stock bikes using the Delphi system and base downloads are probably better off with running the stock 6r12 plug. With the computer and all the other sensors that are providing real time information to the ECM, loosing the value the ECM receives from the 6r12 plug will affect how the engine runs across its operating range. Not all pre-igntion can be heard from the seat so one best error on the side of caution.
 
After re reading this thread, I would add the Screaming Eagle plugs I had would make my bike back fire on the rear cylinder about every 3rd start, HMMM the switch back to stock plugs and the problem is gone, Good thing I did not waste my money on those plugs, they were a gift, now I gifted them to the TRASH:p
 
After reading recommendations from this site on what plugs to buy (stock ones from Harley) that's just what I did. Glad I have you guys to do all my thinking for me:D.
 
You must log in or register to reply here.
Back
Top