Spark plug resistance

Chuck Sea/Tac

Chuck Sea/Tac

Well-known member
I noticed, in the dark, that a couple of plugs were jumping down the porcelain to ground. I pulled one and checked for cracks ect. I cleaned the terminal end, and the center electrode, and ohmed it out. Theses are 3X's by the way. I'm losing 1.9 ohms compared to a new plug. Isn't this a solid piece of metal? Where's the resistance coming from?
I'm running an electronic ignition as well. Thanks Chuck
 
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The center electrode is inserted into the center of the brass connector. I assume it's a slight interference fit. However it appears corrosion sometimes develops within that contact area causing resistance. I have one or two NOS 3X cores that have no continuity whatsoever.
 
Chuck,
Hope not to sound offensive, Plugs are an expendable item. We can't expect miracles from old used up plugs. Sorta' like lookin' at a defunct frosted house bulb, "Well, it sure looks good!!" Bill W.
 
The weird part was the spark bypassing the electrode and jumping 5/8" down the outside of the porcelain to ground. These plugs only have about 3500 miles on them. They seem to jump"ship" just as the rpm s pick up off idle. I know parts fail, but it's odd.
 
Chuck Sea/Tac said:
The weird part was the spark bypassing the electrode and jumping 5/8" down the outside of the porcelain to ground. These plugs only have about 3500 miles on them. They seem to jump"ship" just as the rpm s pick up off idle. I know parts fail, but it's odd.
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That is weird, Chuck,
I thought they were old plugs-----I told the Dog:cool: to make note of this in his "WEIRD HAPPENINGS" notebook. Bill W.
 
1.9 ohms never stopped 10,000 volts. Something else is going on. Is this the coil that is supposed to be on the car or a super high output coil? How do you know it is not jumping the plug gap? Does the engine miss? If a very high voltage it may be a 'halo' effect of the spark jumping the gap and down the side of the porcelain
 
Chuck Sea/Tac said:
The weird part was the spark bypassing the electrode and jumping 5/8" down the outside of the porcelain to ground. These plugs only have about 3500 miles on them. They seem to jump"ship" just as the rpm s pick up off idle. I know parts fail, but it's odd.
Click to expand...

It might be the electronic ignition giving you more volts out to the plug than you get with stock ignition. That higher voltage can find its way through another path (like an oily film on the plug insulator) easier than the lower voltage would. And once it starts, it will follow that path again.

I would not worry about 1 ohm. The current is not much, so the voltage drop is not much (compared to the 20,000 volts available). Clean and dry the outside of the porcelain well on all the plugs and check again for spark leakage. You should be good to go.
 
As far as I know, the "R"in the plug number indicates a resistor element built in to the plug. These are for modern cars, and the resistor helps to suppress the noisy emissions that woudl otherwise mess up your electronics-and your radio reception.
 
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