Does a spark plug wire lose it's efficiency over time or does it just go bad all at once. How often should wires be replaced?

 

My personal opinion is that Spark Plug wires are the BIGGEST SCAM in automotive parts business !

Whats a wire do? it conducts current. That's it. No wear, no degradation of the signal unless it was so far beyond the resistance of the conduit that it melted it.

Bottom line, there is no need to replace wires unless:

the exterior is damaged, cut or cracked

the carbon filament is broken inside from being stretched or kinked (does not carry spark at all)

the boots are damaged, cracked or the wire cap inside the boot is pulled out.

Always buy the size wire (8mm or whatever they are/were) the factory installed. It matters. Size and thickness IS resistance and that can delay the spark in any type distributer and that means oddball knocking and misfiring when there is a late spark or weakened spark from excess resistance in the path (wire).

Some folks will disagree. They will say that wires should be changed every 2 yrs or whatever...I just do not see why? Unless the wire is damaged it is the same today as it was in 1993, or feb 2014. Stay away from the DIY kits...those are too easy to end up with a poor end and the engine suffers.
Its usually boots that are the problem. Wires come in high strength silicone and rubber with nylon wrap and they are fairly tough. Always grease the boots inside with silicone grease that's sold as "boot-grease". Makes removal safer and easier.

 

Thanks, with the price of wires I wouldn't want to buy something that's not necessary.

 

What I've seen happen (twice) is that the carbon filament breaks. After that happens the spark arcs across the gap and eats up the filament. Over time the gap gets bigger and bigger until the arc can't jump the gap any more. Then you have a miss on that cylinder.

I found the last one by looking at the wires in a dark garage. Wire #6 was arcing to the oil dipstick tube. When I pulled the boot off the spark plug it came off the wire -- no longer connected.

 

Is a miss very noticeable? My 85 has a TPIS cam and the idle is a little rough or lopey all the time. I just wanted to make sure every cylinder is getting spark. Will the dark garage method work all the time or is there a better way to check. I changed the spark plugs not that long ago.

 

You want a way I've used for years and I think is better?
Take a set of jumper cables, use either the positive or negative (doesn't matter which), have the garage as dark as you can yet still see things like the wiring, belts and pulleys etc and connect one end of the jumper cables to the frame and run the other end along the wires watching and listening for arcing. I've found some bad wires that way when you couldn't see arcing by itself. It won't find things like broken conductor or bad ends on the plug wires, you'll need to ohm them to check that.
Another is to look for carbon tracking in the distributor cap and the condition of the rotor.

 

I usually change plug wires with my first major tune on any vehicle just to have new ones and usually a custom color to match the engine or vehicle color. Vain maybe but I like em. I know I may be taking good wires off and I dont throw them away in case I need one of them I usually buy MSDs, Accels or Taylor because iof the color choice. I dont buy the really expensive ones and I usually do buy the "universal" kit to cut a custom length. Ive never had a problem with them.

You can check the wires individually with a DVM/Ohmmeter. Each wire should have minimal resistance, each type will vary but generally the least resistance is the best. The wires should be about the same what ever that may be so check them all and if they are about the same and I would say (as an uneducated guess) less than 10 ohms, they should be fine.

Definitely pop open the hood at night and check for the light show. Any sparking is bad so swap them out.

Good luck!

 

As usual, Cliff has made me think and remember something related to his comments...

whenever there is increased resistance in the spark plug wires/system, such as a bad wire or corroded boot contact, the increase in resistance can be seen in the cap and rotor tip.
If the resistance gets too high, enough to cause a misfire, it will try to start arcing in the cap as the rotor passes each pole. The bad cylinder will have a burnt pole inside the cap.
NOT on the post on top of the cap, but inside where the rotor passes by. That's because the resistance makes the spark delay or hesitate and then when there is enough pressure built up, (voltage) it will jump to the pole (arc). This is normally just a field surge but in high resistance situations it becomes a physical arc and you WILL see the copper or aluminum pole with carbon scum from the arcing.

That tell-tale sign leads you directly to a bad wire or plug because the source of the resistance must be after the rotor & cap.

 

As usual, Cliff has made me think and remember something related to his comments...

whenever there is increased resistance in the spark plug wires/system, such as a bad wire or corroded boot contact, the increase in resistance can be seen in the cap and rotor tip.
If the resistance gets too high, enough to cause a misfire, it will try to start arcing in the cap as the rotor passes each pole. The bad cylinder will have a burnt pole inside the cap.
NOT on the post on top of the cap, but inside where the rotor passes by. That's because the resistance makes the spark delay or hesitate and then when there is enough pressure built up, (voltage) it will jump to the pole (arc). This is normally just a field surge but in high resistance situations it becomes a physical arc and you WILL see the copper or aluminum pole with carbon scum from the arcing.

That tell-tale sign leads you directly to a bad wire or plug because the source of the resistance must be after the rotor & cap.

In other words, when the distributer generates a high voltage spark, IF it is unable to discharge easily at the plug TIP where it should, it will discharge that energy somewhere....the next place would be the gap between the rotor and cap, or in the plug wire IF the wire were broken inside....same end result, something gets burnt from the arcing,.

 

The wires look to have been there a while, and I thought it may be time to change them both. What do you all think ? What is a good straight up replacement, size ect. ? I don't want to have to make way for size changes or other issues.

Thank You in advance.

 

I only replace them when I burn one. I will change the plugs every 2 years and roughly 2-4 on the coil/cap/rotor.