Ignition wires Ohm's measurement is way off

[Ferd/289]

I recently looked for a spark arcing in one of my wires. While looking I decided to check the Ohm's readings on the wires in an attempt to pin point a bad wire. Looks to me like different lengths of wire have different Ohm readings. I thought the Ohm reading should be the same for all lengths. Can you determine a bad ignition wire from an Ohm check??

Ferd

[Guest jt240z]

It's normal for Ohms to change per length. Longer wires will have a higher resistance. Wires are rated at so many Ohms/ft.

[Guest zbot43]

I would not use an ohm reading as a test of a plug wire. I work in a shop and we use an scope to check the wires. Most shops don't do that though. I think one of the best ways to look for bad wires is to use a spray bottle filled with water. while the engine is running spray water all over the wires especially around the plug boots. This is the cheapest way I know, and it truly works. At night is the best time to do this. It makes it easier to see the spark jumping. You can usually hear it though. So simply spray the wires and look for arcing. Hit the accelerator, or if the car only does it under load have someone else hold the brake while in drive or reverse loading the engine.

If you have a reading of non-connection, infinity, on your ohm meter then you have a bad wire. But just because a wire passes an ohm test doesn't mean it is any good. Leakage is the biggest problem with wires. It isn't the core that goes bad, but the shield. The spark leaks through the shield to ground. The spark is always looking for the easiest way to ground.

I hope this helps you out. We use a spray bottle everyday in our shop, and it really works.