My car is running a little off and I was wondering how I can test the plug wires to make sure they are allowing the right flow of current threw them?

:patriot:

If you have a volt meter you can run a continuity test

I though the way to test a spark plug wire was the ohm meter setting of the multimeter. The lower the resistance the better.

ohm meter unless you have ignition scope

OR

if you're adventurous, stand in a puddle of water, place one hand on the engine and one on a plug wire end and see if you get lit up :woowoo:

Ohm meter is not really a good test because of possible leakage of insulation under high voltage conditions.(engine running)

Ohm meter is not really a good test because of possible leakage of insulation under high voltage conditions.(engine running)

If you want to get down to the nitty gritty, unless you have something to measure the wires integrity while the engine is running, what would you suggest?

If you have an oscilloscope then we could measure the Kv while it was running, but I don't think many people keep those in their garage. But then we'd still have to compare it to the rest, look at the burn time, and then in the end, pull out our Ohm meters and do a wiggle test.

If you want to get down to the nitty gritty, unless you have something to measure the wires integrity while the engine is running, what would you suggest?

If you have an oscilloscope then we could measure the Kv while it was running, but I don't think many people keep those in their garage. But then we'd still have to compare it to the rest, look at the burn time, and then in the end, pull out our Ohm meters and do a wiggle test.

You'd need a scope and a big voltage divider. Or a ragowski coil to look at the DI/DT trace.
Either way, a simple test is to spray water on them in the dark; if the insulation has been compromised you will see a blue corona glow around where voltage is leaking.
Realistically though, if the wires were bad enough for that to happen, you'd be able to see it. The ohmeter test will tell you if the carbon core is intact.
My policy is to replace them every 3 years or so since they are cheap anyways.

You'd need a scope and a big voltage divider. Or a ragowski coil to look at the DI/DT trace.
Either way, a simple test is to spray water on them in the dark; if the insulation has been compromised you will see a blue corona glow around where voltage is leaking.
Realistically though, if the wires were bad enough for that to happen, you'd be able to see it. The ohmeter test will tell you if the carbon core is intact.
My policy is to replace them every 3 years or so since they are cheap anyways.

Water is good but you need bad insulation for that to work.

Years ago I built up a complete MSD ignition system w/the 2 step and the timing control - the whole thing down to the wires. It used a 6T box. At night the wires glowed blue, no miss fires, you could actually grap the wires with no effect. I had to step up to a sheathed 10mm wire to stop it. But it was pretty.

Water is good but you need bad insulation for that to work.

Well, that's the idea isn't it? To check if the insulation is bad ;)


Years ago I built up a complete MSD ignition system w/the 2 step and the timing control - the whole thing down to the wires. It used a 6T box. At night the wires glowed blue, no miss fires, you could actually grap the wires with no effect. I had to step up to a sheathed 10mm wire to stop it. But it was pretty.

I hear you... Here's a photo of me doing the same; that is $6/ foot wire rated at 50,000 volts, and it is sparking to my finger at only 40kV:
http://i529.photobucket.com/albums/dd339/sampowerlabs/DSC00496.jpg

That is capacitive current transfer; it happens because the voltage in the wire is at high frequency so the insulation is acting like a capacitor and charging/discharging my body tens of thousands of times per second and the current transfer is enough to ionize the air between my finger and the wire.
The problem with that is that it does deteriorate the insulation... You did the right thing by sheeting the wires. Big HV cables are shielded for that same reason.

Well, that's the idea isn't it? To check if the insulation is bad ;)

That is capacitive current transfer; it happens because the voltage in the wire is at high frequency so the insulation is acting like a capacitor and charging/discharging my body tens of thousands of times per second and the current transfer is enough to ionize the air between my finger and the wire.
The problem with that is that it does deteriorate the insulation... You did the right thing by sheeting the wires. Big HV cables are shielded for that same reason.

Water is good and has it's purposes, but it's not the end all.

For the longest time the 3.8 and 4.6 Fords w/the waste spark remote coils had problems with the wires. The car would come in w/a misfire, you could spray the wires and not find the failed one.

My suggestion to you is ,if you suspect the wires are source of problem ,and you don t have any of the aforementioned meters or equipment to test each one, , just replace them with a good quality set ,they aren t that expensive

My suggestion to you is ,if you suspect the wires are source of problem ,and you don t have any of the aforementioned meters or equipment to test each one, , just replace them with a good quality set ,they aren t that expensive

Agreed, I,ve seen wires that have leakage when I run the car in the dark and look at the engine running.
Continuity is not the only purpose of a plug wire,at these high voltages, dialectric strength is extremely important.Thats why the wires( insulation ) are so thick.

A meggar or mega-ohm test can determine the dielectric strength of the insulation.