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Testing New Spark Plug wires ? by StockGT
Started on: 06-01-2008 01:53 PM
Replies: 3
Last post by: StockGT on 06-02-2008 02:39 PM
StockGT
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Report this Post06-01-2008 01:53 PM Click Here to See the Profile for StockGTClick Here to Email StockGTSend a Private Message to StockGTDirect Link to This Post
I have a set of new Spark Plug wires that I measured the resistance with a DVM before installing. I wanted to find out before rather then after installation if any of the wires were bad. The two short wires measured 8.0 k and 9.6 k ohms. The longest wire was 13.6 k ohms. The 2nd longest wire measured at 42 k ohms. The wires are for a Duke with DIS Ignition.

Will the Higher resistance measurement on 2nd longest wire be a problem ?
The resistance on this wire is about three times the measurement on the longest wire. I realize that the meter is measuring DC resistance, and that ignition spark is a high voltage AC signal, which has characteristics different then a DC current. Measuring the 11 year old wires, the resistance varies in proportion to the wire length.
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Dennis LaGrua
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Report this Post06-01-2008 10:54 PM Click Here to See the Profile for Dennis LaGruaClick Here to Email Dennis LaGruaSend a Private Message to Dennis LaGruaDirect Link to This Post
To answer your question, your resistance reading for OEM carbon core wires sound correct. They are usually in that range.
However,ignition wire resistance so large as that weakens the spark. Thats why I use only MSD superconductor wires on all my Fieros.
Stock GM carbon core wires can run 8,000 to 10,000 ohms per wire. Thats a considerable impediment to a strong spark. Standard nickel spiral performance wires can have about 300 ohms per ft of resistance, while stock GM and other carbon core wires can have several thousand ohms of resistance per ft.
MSD Superconductor wire has the lowest resistence of any wire of only 50 ohms per ft. and hence it provides the strongest spark. It also improves the life of your coil(s) as they don't have to work as hard to overcome much resistance to fire the plug.

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theogre
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Report this Post06-01-2008 11:30 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreDirect Link to This Post
The DC resistance of plug wires is actually a pretty useless test and even more meaningless as a marketing tool. It should be considered little more than the most rudimentary measure of wire condition.

High voltages used in things like the Ignition behave much differently than what you get at the voltage your Ohm meter uses or even if you ran 120-240VAC over them. Other than wire quality, IE durability, nearly all wires perform exactly the same because of it. Any quality brand of wire is going to work just fine and last at least a few years. (Assuming you don't jerk the end off one or burn one up from being too close to the exhaust etc.)

I'm not going to even try to explain it. It's fairly advanced electrical practice and even an Ogre has trouble understanding it all, which is why so many wire makers get away with complete BS for marketing. If you've ever seen pictures where lightning is skipping along the surface of things, that is similar to what is happening in a plug wire. That kind of energy barely notices a change of even hundreds or thousands of ohms. It's about to jump an open circuit...

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StockGT
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Report this Post06-02-2008 02:39 PM Click Here to See the Profile for StockGTClick Here to Email StockGTSend a Private Message to StockGTDirect Link to This Post
Thanks for the replies!
Yesterday I cleaned up the old wires, applied some dielectric grease and reinstalled.
I will try the new wires after the car passes it's smog test.
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