Audi A6 + RS6 (1997 - 2004) - HT Leads - replacement time? [as plugs, cambelt?]

Honest John Back Room » Technical matters
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Mon 3 Sep 2007 14:25
HT Leads - replacement time? [as plugs, cambelt?] - John F
How long do HT leads last? I had a bit of hesitant starting 5,000 miles ago [1998 Audi A6 2.8, now 98,000] but all is OK now, so thought it might have been a tankful of dodgy fuel. I bought it at 77,000 with FSH so I am fairly certain they are original.

Is there not an argument for routine replacement as early sign of failure [un-noticed misfiring, especially on engines with more than 4 cylinders] could damge the cat with unburnt fuel? If so, why is this not recommended in the manufacturer's handbook?
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Mon 3 Sep 2007 15:30
HT Leads - replacement time? [as plugs, cambelt?] - GregSwain
HT leads vary in lifespan, and at worst will cause a misfire, which is why they're generally only replaced once they stop working. I doubt an intermittent misfire would cause cat damage if it was sorted soon after being discovered. Most modern cars have low-voltage leads, with a coil pack on each cylinder, and these would be rather expensive to replace every few years.

Anyway, you can't compare a HT lead with a cambelt - the subsequent cost of a cambelt snapping far outweighs the cost of replacing the part routinely. The same cannot be said for an ignition lead (or coil-pack for that matter). Test the resistance of the leads, they should all be similar, and hopefully very low. If not, maybe just replace the one(s) that aren't working efficiently anymore rather than all 6.
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