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I know that Toyota factories mark the spark plugs. I wonder about Honda. I have come upon a used 2013 Civic EX with 110k miles. I removed the spark plugs for the first time today. The plugs are NGK DILZKR7B11GS. How do they look? I am debating whether to replace them. NGK resistance spec for this spark plug is 5 kΩ. I measured the resistance and tested the continuity. All center electrode continuity with tip tested good. All ground continuity with base tested good. No short between center electrode and ground. Gap for each verified to be at 0.044".
Cylinder 1 plug, measured 4.47 kΩ:



Cylinder 2, measured 3.32 kΩ:



Cylinder 3, measured 4.00 kΩ:



Cylinder 4, measured 3.50 kΩ:

 
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I mean, they very well could be. 110k miles isn’t crazy for spark plugs anymore. I think my dad finally did the ones on his Focus ST at like 180k miles after buying it brand new.

 
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You've come this far, just replace them. Never heard of anyone measuring spark plug resistance before.

 
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Isnt NGK aftermarket plugs? Arent Denso the factory plugs? If youre going to replace them, use the original equipment, which I would think is Denso.

 
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Both are:

 
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Can confirm. This is the case with pretty much every Honda.

 
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Per Lela Martin, Technical Support of Aftermarket Division at NGK U.S.A.: "Resistance value between 3,500 ~ 7,000 is within specifications because the resistance value of the plug does not determine the performance at all. The resistance is only there to eliminate electronic frequency interference."

I also inquired about the gaps being narrower than spec'd on some new plugs I bought. Her response: '.004” will not make any difference on the performance. It is actually better to be on the lower side since the gap will wear up.'