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#3128408 - 09/18/13 08:58 AM Multimeter use on spark plug wires
TechnoLoGs Offline


Registered: 04/03/13
Posts: 2606
Loc: Call it NNJ
As to testing them. I have an 8mm coil wire, looks to be in good shape, slightly dirty contacts but I have "Battery cleaner" (the kind that foams up.) I also have a multimeter. I am asking if there is a way to determine if this wire is good by measuring its resistance.

Any normally accepted values for this kind of thing, in Ohms or kOhms or milli-Ohms or ?

We are re-doing the tune-up on the truck.
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#3128416 - 09/18/13 09:04 AM Re: Multimeter use on spark plug wires [Re: TechnoLoGs]
punisher Offline


Registered: 09/11/04
Posts: 2135
Loc: snowblind in TX
In ancient times there was an "ohms/foot" spec for wires. You would hook up your DVOM, or an actual analog meter (watch that needle) and flex the wire and look to see if everything was in spec. If I were doing it now, I would just ohm the wire, and compare it to the others and look for something way out of spec. Truth is, ohming a wire isn't the best test in the world, better than nothing, but not a great test.

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#3128432 - 09/18/13 09:35 AM Re: Multimeter use on spark plug wires [Re: TechnoLoGs]
TFB1 Offline


Registered: 09/03/10
Posts: 2894
Loc: VA
If one looks hard enough there is still ohms per foot given for most wires, common for racers to "ohm out" their wires... The spiral wound wires will have a very low resistance vs the carbon types...

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#3128478 - 09/18/13 10:26 AM Re: Multimeter use on spark plug wires [Re: TechnoLoGs]
dparm Offline


Registered: 04/19/10
Posts: 12612
Loc: Chicago, IL
Factory service manual (the ones that dealer techs use) should have the minimum accepted value for resistance of the wire. My old Integra's did.
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#3128482 - 09/18/13 10:29 AM Re: Multimeter use on spark plug wires [Re: TechnoLoGs]
eljefino Online   content


Registered: 06/15/03
Posts: 26722
Loc: ME
You might need a "megger" eg mega-ohm meter. Your average radio shack $20 model might not do it.

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#3128539 - 09/18/13 11:27 AM Re: Multimeter use on spark plug wires [Re: TechnoLoGs]
MolaKule Offline


Registered: 06/05/02
Posts: 15693
Loc: Iowegia - USA
Many OEM resistance spark plug wires using carbon conductors have around 5,000 to 15,000 ohms of resistance per foot, very much within the measuring capabilities of a common analog VOM or a DVM.

Specialty racing wires with high copper content or special construction will have much lower resistance.

MSD says this:

Quote:
Heli-Core Wires (Blue):
150 - 1,200 ohms per foot

8.5mm Super Conductor (Red):
40 - 50 ohms per foot

If you do not know the specification for your wires, measure the resistance of each wire. Remember to divide the length of the wire by 12 to get a "per foot" measurement. If one wire is out of that average spec, it is at fault

Solid Core Wires: You cannot run Solid Core Spark Plug Wires with an MSD Ignition Control. Solid Core wires do not suppress any Electro Magnetic Interference (EMI) which will interfere with electronics or rev limiters on your vehicle. A suppression style or spiral wound spark plug wire MUST be used.


Some guy on LS1 says he tested various wires:

Quote:
So here's my test. All wires were tested at least 3 times to be sure I have accurate numbers here. Remember, they were all 12.5 inches long. I tested next to a radio but did not pick up any static from any of these wires.

stock LS1 6 in. - 351 ohms

Granatelli 8mm Steel Solid Core Cable - 0.1 ohms
MSD 8.5mm Super Conductor - 71.6 ohms
Accel 8.8 300+ Ferro-Spiral Race Wire - 166.1 ohms
Jacobs Electronics EnergyCore 8.5mm - 178.3 oms
Taylor Spiro Pro 8mm Silicone - 301 ohms
Mallory Pro Sidewinder 8mm Silicone Suppression Wire - 313 ohms
Moroso Blue Maz Spiral Core 8mm - 661 ohms
Magnecor KV85 Competiton 2.5mm - 2053 ohms


Edited by MolaKule (09/18/13 11:41 AM)
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#3128671 - 09/18/13 02:13 PM Re: Multimeter use on spark plug wires [Re: TechnoLoGs]
meep Offline


Registered: 02/20/07
Posts: 2706
Loc: Southeast
ohming them ensures they are conducting and not arcing inside. obviously the long wires will have more resistance, and this is ok.

It will not catch early breakdown in the insulating jacket, where a wire may be arcing to ground and causing a misfire.
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#3128680 - 09/18/13 02:20 PM Re: Multimeter use on spark plug wires [Re: TechnoLoGs]
dishdude Offline


Registered: 11/14/08
Posts: 4472
Loc: Phoenix
I thought you replaced the wires?

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#3128693 - 09/18/13 02:30 PM Re: Multimeter use on spark plug wires [Re: dparm]
stephen9666 Offline


Registered: 12/08/06
Posts: 2874
Loc: USA
Originally Posted By: dparm
Factory service manual (the ones that dealer techs use) should have the minimum accepted value for resistance of the wire. My old Integra's did.


This.

I know I've seen this spec in my FSMs.

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#3128992 - 09/18/13 07:55 PM Re: Multimeter use on spark plug wires [Re: meep]
JetStar Offline


Registered: 10/02/08
Posts: 1105
Loc: Flatlands of Indiana
Originally Posted By: meep

It will not catch early breakdown in the insulating jacket, where a wire may be arcing to ground and causing a misfire.


Bingo, "Any good" means that they are conductive where they should be and don't arc through the insulation to ground. Both will cause misfire. To test the insulation properties, you would need a Hi-pot / dielectric tester capable of at least 20 Kv and a ground rod to sweep the exterior looking for flashover. probably not worth the hassle. Probably easier to check them out for arcing at night.


Edited by JetStar (09/18/13 07:56 PM)
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#3129060 - 09/18/13 08:53 PM Re: Multimeter use on spark plug wires [Re: TechnoLoGs]
TechnoLoGs Offline


Registered: 04/03/13
Posts: 2606
Loc: Call it NNJ
^^^ I just misted water onto all electricals at night in the dark and I saw NO light show, AT ALL! This is desired result, yes?
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12,359 10/22 12,361 10/23 12,365 10/24 12,369 10/25

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#3129122 - 09/18/13 10:28 PM Re: Multimeter use on spark plug wires [Re: TechnoLoGs]
punisher Offline


Registered: 09/11/04
Posts: 2135
Loc: snowblind in TX
Originally Posted By: TechnoLoGs
^^^ I just misted water onto all electricals at night in the dark and I saw NO light show, AT ALL! This is desired result, yes?


You know, we had $100k+ of electrical/ignition/computer testers in the shop, and a spray bottle was still the fastest/easiest way to find a bad wire.

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#3129199 - 09/19/13 01:33 AM Re: Multimeter use on spark plug wires [Re: TechnoLoGs]
ram_man Offline


Registered: 03/15/13
Posts: 2148
Loc: southern mo
Originally Posted By: TechnoLoGs
^^^ I just misted water onto all electricals at night in the dark and I saw NO light show, AT ALL! This is desired result, yes?


That is the redneck way. It tests the wires insulation. Honeslty when I check them I do them all and if one has a resistance way higher than the rest I get all new. As long as they are fairly even accross the board theyre ok.
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#3129354 - 09/19/13 08:22 AM Re: Multimeter use on spark plug wires [Re: ram_man]
dishdude Offline


Registered: 11/14/08
Posts: 4472
Loc: Phoenix
Originally Posted By: ram_man
Originally Posted By: TechnoLoGs
^^^ I just misted water onto all electricals at night in the dark and I saw NO light show, AT ALL! This is desired result, yes?


That is the redneck way. It tests the wires insulation. Honeslty when I check them I do them all and if one has a resistance way higher than the rest I get all new. As long as they are fairly even accross the board theyre ok.


Sometimes the simplest test is the best.

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#3129438 - 09/19/13 10:07 AM Re: Multimeter use on spark plug wires [Re: dishdude]
hsd Offline


Registered: 09/05/09
Posts: 242
Loc: NE
Originally Posted By: dishdude


Sometimes the simplest test is the best.


Just run fingers along the wires while its running cry

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