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Old 06-27-2009, 09:26 PM
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plug wire ohms

Does anyone know what the ohms range is for spark plug wires? They are on a 1974 350 engine and the engine has points. Any other way to tell if they are bad? The engine misses and i am thinking the wires may be bad because the points/coil/and distributor cap are new. I haven't done a cylinder leak test to check the valves, but the engine doesn't smoke, so I hope the vales are good. Thanks for any help and advice...
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Old 06-27-2009, 09:28 PM
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The higher resistance they are the worse. If they are old or you are in doubt just replace them.
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Old 06-27-2009, 10:07 PM
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Simple.

Just measure the resistance of each wire while wiggling the wire.
Not likely for all wires fail at the same time; so just verify all wires have similar resistance per foot. In other words the short wires will have lower resistance than longer wires.

Another test is to inspect the wires during idle at night. Look for any sparks while wiggling wires. Wear rubber gloves or else you may get a shock from a leaky wire.
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Old 06-28-2009, 07:50 AM
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Quote:
Originally Posted by weirdbeard
The higher resistance they are the worse. If they are old or you are in doubt just replace them.
Eventually I will replace them, but i am trying to determine if i have a bad wire or a problem with a valve. I figure it is easier and less expensive to check the wires than to do a leak down test....although i cant see any smoke or smell excessive gas it does skip and pop from time to time. Any advice is appreciated
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Old 06-28-2009, 08:12 AM
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Can i get some input on making plug wires versus buying them already put together? Are there any special tools and tricks that one might want to know? I know a crimper is needed, but is there a special type or can a standard electrical crimper be used?
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Old 06-28-2009, 08:23 AM
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From the "old school"--The average resistance reading for plug wires is 10K per foot. I will also use a windex type spray bottle with water in it and spray the wires while engine is idling--any LEAKING wires will usually show themselves at that point. Use the "wiggle" method with your meter as suggested to find an intermittent BROKEN wire. High resistance wires most often misfire under load but otherwise will seem to be OK. If in doubt--Throw them out.
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Old 06-28-2009, 11:09 AM
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Things You'll Need:

* Volt meter tester
* Dielectric grease
* WD-40
* Rags or shop paper towels

1.
Step 1

Remove only one wire at a time. If it is a used wire, start out by wiping down the wire with WD-40, since your visual inspection will be easier with a clean wire. Be sure the metal clips within the boots at each end of the wire are clean, corrosion free and in good condition.
2.
Step 2
Typical volt meter tester
Typical volt meter tester

Prepare your tester and set up on the OHM test section on the meter at 20,000, or 20k.
3.
Step 3

Measure the length of the wire, since the length is a factor you must know to determine test results. To test, hold the positive, or red, probe into one end, being sure to have contact with the metal clip in the boot and the negative, or black, probe into the other end.
4.
Step 4

Your readings may jump around at first but should stabilize after a few moments. A shorter wire with a length of 12 inches may test out between 6.00 to 7.00 ohms and a longer wire of 30 inches may measure out between 9.00 and 11.00. A 24-inch wire may come in between 7.50 and 9.00 ohms. All of the above readings would put you in a normal range. Any reading less than 6.00, regardless of the length, would represent low resistance, and that wire would be best off replaced.
5.
Step 5

If your readings are satisfactory and you are going to install the wires, apply a small amount of dielectric grease on the inner portion of the metal clips within the boot to help insure the boot will not get stuck to the plug and to prevent arcing.
6.
Step 6

Install your wire back to the plug and location on the distributor cap from which it came and be sure that the wire is secure at both ends. You may tug on it a bit after installation to be sure you have a proper fit. If you have a problem securing a connection, sometimes you can work with a needle-nose pliers to reshape the metal clips within the boots for a more secure fit.

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Old 06-28-2009, 05:14 PM
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Quote:
Originally Posted by richard stewart 3rd
Things You'll Need:

* Volt meter tester
* Dielectric grease
* WD-40
* Rags or shop paper towels

1.
Step 1

Remove only one wire at a time. If it is a used wire, start out by wiping down the wire with WD-40, since your visual inspection will be easier with a clean wire. Be sure the metal clips within the boots at each end of the wire are clean, corrosion free and in good condition.
2.
Step 2
Typical volt meter tester
Typical volt meter tester

Prepare your tester and set up on the OHM test section on the meter at 20,000, or 20k.
3.
Step 3

Measure the length of the wire, since the length is a factor you must know to determine test results. To test, hold the positive, or red, probe into one end, being sure to have contact with the metal clip in the boot and the negative, or black, probe into the other end.
4.
Step 4

Your readings may jump around at first but should stabilize after a few moments. A shorter wire with a length of 12 inches may test out between 6.00 to 7.00 ohms and a longer wire of 30 inches may measure out between 9.00 and 11.00. A 24-inch wire may come in between 7.50 and 9.00 ohms. All of the above readings would put you in a normal range. Any reading less than 6.00, regardless of the length, would represent low resistance, and that wire would be best off replaced.
5.
Step 5

If your readings are satisfactory and you are going to install the wires, apply a small amount of dielectric grease on the inner portion of the metal clips within the boot to help insure the boot will not get stuck to the plug and to prevent arcing.
6.
Step 6

Install your wire back to the plug and location on the distributor cap from which it came and be sure that the wire is secure at both ends. You may tug on it a bit after installation to be sure you have a proper fit. If you have a problem securing a connection, sometimes you can work with a needle-nose pliers to reshape the metal clips within the boots for a more secure fit.

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Wow, thanks for this very good information. According to your post, not only do I have a bad wire, all my wires are bad. I set my meter on 20k as you said and my readings range from 1.34 up to 2.01 and the coil wire is even lower at .51.
It looks like i need some wires, my wires are reading very low. Thanks for the help....
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Old 06-28-2009, 05:23 PM
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All the years I have been doing tuneups, a plug wire should ohm at 2K per foot.
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Old 06-28-2009, 05:38 PM
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Back in the day, I used to use that yellow Accel solid core wire on everything, along with no-resistance plugs. The wire ohmed at ZERO per ft., but played hell with anything electronic, including my neighbor's television set.

Last edited by techinspector1; 06-28-2009 at 05:45 PM.
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Old 06-28-2009, 05:52 PM
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Solid core plug wires...I have not installed a set of them in anything in years. IIRC, MSD does not recommend them either, for use with the 6AL box.
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Old 06-30-2009, 07:44 PM
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I bought new wires today and although i haven't put them on my truck yet, I did check the ohms. The old wires ranged from the coil wire (.51) to the longest wire at (2.01) and the new wires range from (3.0) to (12.0) with the meter set at 20k.
I bought a small tube of dyelectric grease and have heard mixed comments about it. I was going to use it on the inside of the plug boots, but i read it may get hard and brittle? Any comment good or bad on this type grease?
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Old 06-30-2009, 09:01 PM
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Quote:
Originally Posted by richard stewart 3rd
Things You'll Need:

* Volt meter tester
* Dielectric grease
* WD-40
* Rags or shop paper towels

1.
Step 1

Remove only one wire at a time. If it is a used wire, start out by wiping down the wire with WD-40, since your visual inspection will be easier with a clean wire. Be sure the metal clips within the boots at each end of the wire are clean, corrosion free and in good condition.
2.
Step 2
Typical volt meter tester
Typical volt meter tester

Prepare your tester and set up on the OHM test section on the meter at 20,000, or 20k.
3.
Step 3

Measure the length of the wire, since the length is a factor you must know to determine test results. To test, hold the positive, or red, probe into one end, being sure to have contact with the metal clip in the boot and the negative, or black, probe into the other end.
4.
Step 4

Your readings may jump around at first but should stabilize after a few moments. A shorter wire with a length of 12 inches may test out between 6.00 to 7.00 ohms and a longer wire of 30 inches may measure out between 9.00 and 11.00. A 24-inch wire may come in between 7.50 and 9.00 ohms. All of the above readings would put you in a normal range. Any reading less than 6.00, regardless of the length, would represent low resistance, and that wire would be best off replaced.
5.
Step 5

If your readings are satisfactory and you are going to install the wires, apply a small amount of dielectric grease on the inner portion of the metal clips within the boot to help insure the boot will not get stuck to the plug and to prevent arcing.
6.
Step 6

Install your wire back to the plug and location on the distributor cap from which it came and be sure that the wire is secure at both ends. You may tug on it a bit after installation to be sure you have a proper fit. If you have a problem securing a connection, sometimes you can work with a needle-nose pliers to reshape the metal clips within the boots for a more secure fit.

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Get Current & Comprehensive Info on HIV Resistance Testing & Education
www.Resist-HIV.info

Resistance Meter
0.1u-ohm to 110M-ohm High Accuracy & High Speed
www.hiokiusa.com

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You have a wealth of knowledge there. I have a question for you. I have a 347 ford with new edelbrock heads and the question of whether to use a spark plug anti-seize paste off the shelf, or not ,as some say the paste can actually weld the plug thread into the head if it has ceramic content in it. One mechanic on the web uses Bel Ray assembly lube, others use grease or oil. I have quizzed them at edelbrock but no response as yet. I recently took out a plug from an alloy headed 4 litre engine with two threads of alloy jammed in the thread. Consequently a helicoil was needed.
Any suggestions welcome
Al from Aus.
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Old 07-01-2009, 04:42 PM
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Quote:
Originally Posted by tcoop
I bought new wires today and although i haven't put them on my truck yet, I did check the ohms. The old wires ranged from the coil wire (.51) to the longest wire at (2.01) and the new wires range from (3.0) to (12.0) with the meter set at 20k.
I bought a small tube of dyelectric grease and have heard mixed comments about it. I was going to use it on the inside of the plug boots, but i read it may get hard and brittle? Any comment good or bad on this type grease?
On the dielectric grease, it should not get brittle... only use it on the plug boots not the dist boots. Its purpose is to keep the boots from sticking to the plugs (but given enough time & mileage they may anyway). Dont over-do it, just a light coat on the inside of the boot is sufficient.

One thought about ohming wires, there are some brands that tout low resistance (like 50 ohms per foot) and still claim to have decent supression capabilities (supression of RFI is what lets the wires work without causing problems like the solid cores mentioned earlier) ... just because you check ohms and the reading is low does not mean they are in need of replacement.

BTW, you asked earlier about a crimper, I'd venture to say most use an electrical crimper but MSD makes a good one that goes in a bench vise.

Last edited by Mad_Max; 07-01-2009 at 04:57 PM.
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