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Thread: Spark Plug Leads ?

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    Default Spark Plug Leads ?

    I replaced a set of Spark Plug Leads on a GU Patrol 4.5L Petrol yesterday
    I just did it as a matter of course while changing the spark plugs and doing the filters.

    The plugs i removed where in near perfect condition and leads in perfect condition
    Bright shiny ends where they plug into the distributor and connect to the spark plug, nice flexible silicon leads, no marks on them, nothing

    I replaced them a some 8mm silicon leads, which subsequently were too fat to fit in the stock lead holders, making this a bit messy.

    I know they say to change leads after a certain amount of km's...... But why?
    Does the actual cable break down?? Or is it the terminations begin to become high resistance or something?

    Engine ran perfectly smooth and quite before, same after.....

    So, what is it with leads needing to be replaced at a certain interval???
    If u want to go on an expedition get a Land Rover, if u want to come home from an expedition get a Landcruiser!



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    I replace only when there is an obvious problem, which I can't remember the last vehicle I changed leads on.
    Oh yes I do it was my HG Monaro about 40 years ago & I did it because I built a new engine & wanted nice bright yellow leads on it for some bling.
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    In old days we used copper wire in leads, but very rf producing. So carbon type leads were developed. These break down over time/use, so need to test/replace periodically. Quick test is resistance measurement.

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    Quote Originally Posted by Tom Mix View Post
    In old days we used copper wire in leads, but very rf producing. So carbon type leads were developed. These break down over time/use, so need to test/replace periodically. Quick test is resistance measurement.
    Yes & if they test OK no need to replace.
    Now new engines have no leads; each spark plug cap is a coil, so only ordinary low voltage wires run to each.
    Cheers, Tiny
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    way back when we used to take the carbon leads out and bash them on the concrete to lower the resistance as the carbon would end up on the lowest point and a good bash would re distribute it thru the lead again. they were made of raw fiberglass drawn thru carbon dust inside a plastic sheath theres some history for ya
    . Please treat people as you would like to be treated yourself.

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    I don't replace leads very often only when I start to get a miss after I've replaced the spark plugs. Old VT Commodore prob had them changed twice in 435,000km.

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    depends on the car and how the leads are utilised to some extent. on my previous Pajero there was never anything wrong with the wires themselves . but - because the plugs were buried deep into the head they sat at the bottom of long stainless tubes , and the rubber insulating boots over time would crack open causing a spark loss to earth inside the tube. This sort of misfiring issue is hard to find so it was reccommended they be replaced at 150k or so.

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    LSemmens
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    Leads? What are they? Haven't been anywhere near them since late last century!!!
    I'm out of my mind, but feel free to leave a message...

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    Thanks guys, that is about how i've seen it
    There is no degradation the in the lead itself, but maybe the terminations

    I have only ever seen degraded Spark Plugs, not leads before.
    But have changed both as part of being thorough.

    Everytime i have, the leads i've removed look perfect
    If u want to go on an expedition get a Land Rover, if u want to come home from an expedition get a Landcruiser!

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