What Should Ohm Reading Be?

You're fine estimating the length and calculating off that. There should be no resistance in the cap terminals or extenders so you do not need to remove them

 

Only if you want to measure just the wire itself. First, remove the wire from the cap, cut off ~1/4", and then repierce the wire with the pointed retaining screw. Then make the resistance measurement for the whole food chain (from the contact inside the cap to the clip at the end of the extender. If still no good, then measure the individual components. The surface of the contacts inside the cap can get oxidized so you might need to "dig" the meter probe into the contact material a little bit, or file off a clean place (in a non-functional area) to touch the probe.

 

I found the screw in the distributors that holds the wire and makes contact didn't always make a good contact when measured with an ohm meter ... but she still seemed like she was running/firing on all 8. It made me worry about removing the caps and disturbing the connections if/when I would have a continuity reading. I think the material of the conductor and the diameter of the wire effect the connection. The smaller wires from the factory work better I figured because they can shove the wire to the side and the pin/screw will make better connection ... maybe? It seemed like if it pierced the very center of the wire I'd have the intermittent connection. I played with them on the bench and they just seemed really finnicky ... my .02

 

Because the wires break inside but the spark will jump the gap, so the engine will still run - but as you would expect performance then deteriorates over time & eventually it will mis-fire

Before I changed mine (for new OEM wires) I measured the old ones 2 or 3 times & they came in between about 700 & 1150 depending on lead length - and they really didn't change over time. I measured the brand new set & they were basically the same.

Within 6 months of the previous test on the old wires I had them off again to find that 3 of them had broken in the intervening period. It seems that once they start to go the can all go fairly quickly.

 

I always found this to be due to the connection in the cap and not a break in the actual wire .... whenever I removed a wire and just tested the conuctor from end to end it was fine ... .02 more ... edit: then installed coil on plugs 6 years ago and stopped worrying about it

 

I tested them out of the caps to check that, then shortened them a little & checked again, they were broken.

I automatically test them end-end from the cap to the end of the extender now whenever I take a cap off.

 

Looking carefully at the end of the wire, it is actually wound around a non-conductive core. If you try and measure at the core, you will get infinite resistance. Also, the wire may be coated or oxidized, I can't remember, so you have to scratch the surface of the thin wire to be able to get a reading.

But don't be too alarmed about bad conduction. The spark will get through even if there is no direct metal-to-metal connection. I usually think, as a guideline in air, 1mm/kV. If the gap is larger than that, the spark might not happen. In case there is an isolator in between the two metal surfaces, the gap has to be much smaller, of course.

As an example in air - if I have 6kV across a gap of 6mm - then I will probably get a spark. If I have 10mm - I will not get a spark. With 1mm, the spark is guaranteed.

 

I don't know what 3M heat shrink is capable of, but I just wanted to mention that I used polyimide tape (such as Kapton from DuPont) to insulate my electrostatic speaker panels. The voltage in these speakers are much lower than in an ignition system, but the tape is very capable, in the region of 300kV/mm in dielectric strength. I guess you should have at least 60kV strength to be on the safe side, which would suggest 0.2mm thick tape.

 

The resistance is DC-measured, I assume. It does not say much about the performance of the wire. It does tell you that a low-resistance wire might have fewer turns (wound wire around a core) than a wire with higher resistance.

To be sure what to order, there should be a kind of "spark energy" comparison chart ... but I don't know if this exists.

In general, a straight wire with low resistance would be nice to produce a high-energy spark, but the downside of this would be a completely ruined radio reception or inoperable electronic ignition system. Things might not break - but just temporarily fail to operate with the wrong spark wires.