Spark plug wire test
Thread Starter
Rennlist Member
Joined: Mar 2004
Posts: 190
Likes: 4
From: San Diego, CA
Spark plug wire test
I have ordered new distributor caps and rotors that I will install next weekend; it looks like a straightforward DIY job. The specialist said that when they do this, they also do an ohm test on the plug wires to check their condition. Can I do this test with a basic digital multimeter and how is it carried out? I did a forum search, but found nothing on this topic. As far as I know, these are the original plug wires at 140K miles, and the engine is running just fine.
Burning Brakes
Joined: Jun 2004
Posts: 762
Likes: 10
I'v enever done it on plug wires before, but I'm assuming its just like any other ohm-meter continuity test on a wire. Make sure your battery is good in the ohm-meter because its going to provide power for the test. I think you're going to need an alegator clip for at least one end, and probably both.While your plug wires are disconnected, you're going to connect the meter to either end of each wire, one at a time. Set the meter to the "Omega" for measuring resistance and turn it on. Basically all it's doing is sending a current through the wire to measure resistance from one end to the other. I have no idea what is the proper resistance for a plug wire to demonstrate uninterrupted continuity, but I'm sure someone can provide that.
Burning Brakes
Joined: Oct 2005
Posts: 828
Likes: 0
I know this is crude but run the engine in the garage with lights off and hood up. If the insulation of a wire is bad, you will see it light up. Or you could run a long screw driver with a plastic handle along the wires and that will cause a spark to jump to the screw driver too. Obviously, you DON'T want to do this in complete darkness with the engine running for numerous safety reasons. Better yet, if the wires are that old and you are changing out the caps anyway, might as well do the wires and forget about it.
Three Wheelin'
Joined: Oct 2002
Posts: 1,879
Likes: 3
From: Pasadena, MD - Land of Taxes
Ian... The distributor cap swap is very easy to do. While you're under there you may want to clean your ISV too. To make it easier... You may want to number the wires with masking tape so you can ensure that you get the correct order going back on.
At 140k miles... I think I'd go ahead and replace the plug wires too. Just my .02
At 140k miles... I think I'd go ahead and replace the plug wires too. Just my .02
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Thread Starter
Rennlist Member
Joined: Mar 2004
Posts: 190
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From: San Diego, CA
Thanks to all of you for the helpful advice. I do plan to replace the plug wires, but after doing the clutch and flywheel already this month, they will have to wait a while and which is why I am wanting to just test that they are OK for now. Thanks for the ISV suggestion, Rick, I hadn't thought of doing that.
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Racer
Joined: May 2004
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From: Kent, Great Britain
The plug leads should have some internal resistance as they also act as RF suppresion 2.8k is about right from memory (there may be a factory spec!). What your really looking for, are any that are completely oc (open circuit). I remember changing a set on my older Carrera 3.0 . it's suprising how "well" a six cylinder engine runs with poor leads. And equally suprising how much improvement good leads are.
Nordschleife Master
Joined: Sep 2004
Posts: 5,061
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From: not in HRM
"That may be, but the new wires factory wire set I have for my car measures 2800ohms for a 2.5' length. That is more like 1120ohms per foot."
Is that boot to boot or just the wire ?
I'm going to dig out my spare set and kenwood bench dmm and check um out .
"The plug leads should have some internal resistance as they also act as RF suppresion"
Last I looked , my wires were metal . Not all wires are made the same .
Is that boot to boot or just the wire ?
I'm going to dig out my spare set and kenwood bench dmm and check um out .
"The plug leads should have some internal resistance as they also act as RF suppresion"
Last I looked , my wires were metal . Not all wires are made the same .
