Ignition and coil wires...replace or not?

when the wires go, you get misfiring. Probably most noticable at idle or stumbling when blipping the throttle.

An inductive timing light shows the problem as an irregular "heartbeat" in the strobe.

You can also pull the distributor caps and use an ohmeter to measure the wire resistance, but make sure you flex the wires some. On my 328, the core on wire to cylinder #7 was toasted. It ohmed ok initially, but bending the cable would cause it to go open as the spiral wire separated, and you could feel/hear the core cracking. Cylinder 8 wire was also deteriorating.

Other symptoms were inconsistent starting fast idle rpms (sometimes 1900, sometimes 1600, etc) and occasional lighting of the slow down light, but not due to cat temp...gotta look at the schems to see if feedback from the O2 sensor would cause one of the ECUs to turn on the light...I didn't think so, but the only other explanation is my cat ecu is heading south).

Since this happened right before a long holiday weekend, ordering a prebuilt cable set wasn't possible, so I made a $60 set from 8mm taylor spiral wires. I reused the red plug well boots and wire terminals (you can thread a new wire into the red boots, it just takes a metal tube and a bench vise to do it).

Putting the red sleeves back over the 8mm cable to get the complete oem look is possible, but painful, so after proving it could be done on one wire, I removed it and skipped the rest. 7mm wire would slide in easily...which is what the black cavis wire is. Besides, this is experimental, and following the convention established by Aristotle, all experimental ignition systems must be purple (yeah, purple...the shop had every wire color taylor makes except red in stock).

The taylor wires are about 20% lower resistance, and I'm seeing higher RF interference in the rear laser detector, though that may be just stupid cable routing. I'd check the radio, but I disconnected the amp.

People have used accel wires too. I was going to check out kingsborne wires...maybe still will. I believe carl rose made a comment about his car not liking the wires he tried, though.

I also tried a KAL spark analyzer box I got off ebay which measures kV and burn time. It definitely showed a problem, but it's not working on the taylor wires. I need to check it on another car to see if it's the box or the wire construction causing an issue.

the bad wires were probably original, and if so, lasted 44K miles. Not too bad.
Also changed the plugs (misfires cause fouling) and oil (unburned fuel contamination)

 

To step back a layer, replacing components with the same components isn't going to yield a significant performance increase unless the original components are broken. If it's broken, then replacing the broken parts means it's not broken anymore. If you're being told to replace your coils, "just because", then get suspicious.

If it ain't broke, don't fix it. (Of course, with ignition systems, "broke" can be subtle.)

So I think your question comes down to: "Do ignition components get 'tired' over the years?"

I think the answer to that one is, when they wear out, the ignition system is "broken".
Replacing parts without symptoms ... a tangled web.

 

You asked about wires, and old ones will give weaker sparks and promote fouling. As part of my fouling problem I replaced my wires; I can't say they helped but new wires every few years is a good idea anyway. But don't neglenct the coil itself.

I had a 30 year old coil in my Lotus, and over a period of 6 months it went from instant start, to crank and start, to crank crank crank and start, to not starting at all. I replaced the wires (not that old), the rotor, the distribtor cap, all to no effect. Then I replaced the coil. The car now starts right up like a new car.

Ken

 

Well Ken gave you the hint: check your plugs. If your wires are going south, you should see indications on the plugs: fouling or carbon deposits.

If you're getting indications that your plugs are too cold when you're using hot enough plugs for your driving, then your wires may be the culprit.