Thread: What is the conductor in spark plug wires?

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  1. #1 What is the conductor in spark plug wires? 
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    I was changing the spark plugs in my Land Rover last night and broke the end from one of the wires when I pulled it off the plug. I would have assumed the conductor to be copper strand wire, but it seemed non-metallic. It was a stranded material about 1.5 mm diameter that was similar to glass fiber (like you'd find in fiberglass w\o the resin) that was wrapped in a black plastic sheath, then had the normal insulation around that. I've never seen this before, anybody know what it is made of?
    Last edited by FearTheDentist; 06-15-2010 at 01:35 PM.
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  2. #2 Re: What is the conductor in spark plug wires? 
    Senior Member Lifetime Supporter Colorado 5.9's Avatar
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    It's most likely a carbon core.
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  3. #3 Re: What is the conductor in spark plug wires? 
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    Looks like it is fiberglass; stolen from the interwebs:

    CARBON (SUPPRESSION) CONDUCTORS

    Carbon conductors are used in original equipment ignition wires by most vehicle manufacturers, and in the majority of stock replacement wires. This style of ignition wire is cheap to manufacture and generally provides good suppression for both RFI (radio frequency interference) and EMI (electromagnetic interference). Conductor usually consists of a substrate of fiberglass and/or Kevlar over which high-resistance conductive latex or silicone is coated, and functions by reducing spark current (by resistance) to provide suppression a job it does well while the conductor lasts. Vehicle manufacturers treat ignition wires as service items to be replaced regularly, and limited life is never an issue. This type of conductor quickly fails (burns out) if a high-powered aftermarket ignition system is used.

    SOLID CORE CONDUCTOR WIRES

    Solid metal (copper, tin-plated copper and/or stainless steel) conductor wires are still used in racing on carbureted engines, but can cause all sorts of running problems if used on vehicles with electronic ignition, fuel injection and engine management systems, particularly if vehicle is driven on the street — and damage to some original equipment and modern aftermarket electronic ignition and engine management systems can occur. Solid metal conductor wires cannot be suppressed to overcome EMI or RFI without the addition of current-reducing resistors at both ends of wires.
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  4. #4 Re: What is the conductor in spark plug wires? 
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    Google, imagine that (doh!). That's pretty nifty- I had no idea there was such a thing as conductive silicon or latex- I thought one of silicon's virtues in commercial applications was it's capacity as an insulator (although I guess "semi-conductor" suggests it has some conductivity...).

    Fortunately I was able to just strip it back a bit and crimp the end back on, because replacing the wire would have been a bitch (in brilliant fashion, the designers put the distributer (or whatever you call it in an EFI engine) directly behind the motor where it is almost completely inaccessible).

    I picked the Land Rover up a few weeks ago for a song and dance (less than half of book value, although you do have to keep in mind it is a Land Rover built with world reknowned British engineering, so "book value" is a slippery concept...). It had one significant issue, but the prior owner didn't know it was covered by a recall and just wanted to dump it. It did run a bit rough and seemed rather underpowered for a V-8, but I just attributed this to the aforementioned British engineering and high mileage. Well, last night I spent a few hours last night changing oil, plugs etc just to make sure all the maintenance was up to date. I'm wondering if the PO had the wrong plugs in- they were the "splitfire" type and did not appear to be in bad shape, but I thought I read somewhere these aren't necessarily a good idea in motors not designed for them, so I replaced them with stock. I'm stunned by the improvement- the rough idle is gone and it actually accelerates like a V-8 now. It's still one f'in ugly truck though..
    Last edited by FearTheDentist; 06-15-2010 at 06:13 PM.
    2004 WJ 60\14b ARB\lockrite 37" Nitto mud grapplers

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    If there's one thing I like more than Moab and Grand Cherokees, it's a little boy on boy action.
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