Why change spark plug wires?

[sven556]

I'm looking at doing a full tune-up on my truck and I can't explain to myself why the spark plug wires need to be replaced.. ever. Unless one wears through and grounds out....I'm not aware of any other wires that get replaced as part of routine maintenance. Please somebody set my mind at ease, and explain this to me!

[kstruckcountry]

Eventually the "fibers" in the wires break down so they don't work as well. Old wires are also more likely to arc to nearby metal, hurting the efficiency and leading to electrical problems.

 

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[SurFire]

Over time the insulation is weakened and will "leak" voltage by arching or the wires themselves will corrode and weaken and cause higher resistance causing a weak spark. If your plug wires are not working efficiently you will experience problems such as misfires, causing poor engine performance and poor gas mileage, even premature failure of other ignition components.

 

The reason you replace the plug wires and not others is because of the voltage that is ran through them vs all the others and the actual material used in plug wires. Unlike most of the other wires, which are copper, plug wires are made from carbon strands which deteriorate over time and there is much higher voltage ran through them which is produced by the ignition coil.

[Duelin]

If and when you understand the reason for changing the wires make sure you don't buy cheap wires. If you do you will probably end up with more problems than you started with. Good wires should be able to handle 30,000 to 60,000 volts.

Oh! and the other wires in your truck that don't have to be replaced and are made of metal carry between .01 to 15 volts.

[TimmyG]

I always assumed it was also due to corrosion in the boots

 

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[sven556]

Thanks for the replies. I thought I had responded already... Anyway, thanks for the information. I knew the voltage was in the thousands of volts but I didn't think it was in the tens of thousands of volts, and I never have heard of carbon strands being used for a flexible conductor! I'll have to look into that.

[Blazerblitz]

If you sort of roll/squeeze the wires through your fingers and they feel squishy like a water ballon, it's time to replace them. Heat and time will ruin just about anything around an engine. This 'plumpness' will build up first near the boots and/or surfaces that are too close to direct engine heat. Having good aftermarket looms can extend the life of the wires, but stuff eventually wears down like the other folks are saying. It's not like this is all that expensive to change out, though. Plenty of room to work with also - not like a 90s S10