Spark plug wire findings on resistance...Helpful info inside

[EliteConcept]

Changed my plug wires today after 65,800 miles. Truck ran fine, got fairly decent MPG...around 18 MPG average. When i pulled all the plug wires off i put a multimeter on them to find the resistance, because i wanted to compare it with that of the new wires heres what i found, for reference by others if someone ever needs it or is just wondering...

Old Motorcraft wires using the numbering on the stock wires.
Plug Wire #1 - 12.62 K ohms
Plug Wire #2 - 11.25 k ohms
Plug wire #3 - 11.11 K ohms
Plug wire #4 - 7.43 K ohms
Plug wire #5 - 6.35 K ohms
Plug wire #6 - 5.30 K ohms



Brand New Autolite Pro Plugs
I defined the plug wire number by which plug i put it on.

Plug wire #1 - 6.86 K ohms
Plug wire #2 - 6.78 K ohms
Plug wire #3 - 5.93 K ohms
Plug wire #4 - 4.47 K ohms
Plug wire#5 - 4.26 K ohms
Plug wire #6 - 3.4K ohms

Maybe this will help some of you in the furture

 

[mhn3773]

ok just so i understand....resitance is bad so the less the better right? i know im slow =)

 

[EliteConcept]

yeah, you want your wires to have as little as resistance as possible.
Also remember that the long the wire the greater its resistance gets.

 

[Runnin'OnEmpty]

EliteConcept, interesting comparison. That seems to confirm that spark plug wires do indeed wear out.....

 

[mrboyle]

Generally if a wire has more than 10ohms of resistance its time to replace them.

 

[EliteConcept]

Originally posted by mrboyle
Generally if a wire has more than 10ohms of resistance its time to replace them.

But the shorter wires that have lower initial resistance may never actually reach 10 k ohms

Runnin'OnEmpty
Are you mocking me?

 

[MrShorty]

I think the usual way of "defining" bad wires is a resistance/foot of wire. Chilton's lists it as greater than 7K ohms/foot. Since most spark plug wires are probably less than 1½ feet long, 10K ohms is probably a good rule of thumb. Do you have the lengths of those wires?

 

[EliteConcept]

i didn't measure them but i can, i still have my old wires, and the new wires were about 3-5 inches longer than the stock ones

 

[Runnin'OnEmpty]

Runnin'OnEmpty
Are you mocking me?

No, no, no, Elite! I'd never mock you. Sorry if it sounded that way.....

My thoughts were that a lot of plugs and wires are replaced unnecessarily. The only way to know for sure is to do what you did, and take a resistance measurement. I've always heard that a ballpark figure is about 5K ohms per foot of wire. Any more than that and the wire is suspect.

I once had a Mustang that ran 125K miles on the same set of sparkplugs. I would clean them periodically; sharpen the electrodes and check the resistance. They always checked out at around 2-3K ohms resistance, if I remember correctly. Since the resistance was OK, I didn't see a reason to change them. They were Motorcraft's from the factory, and never missed a beat. (After 125K, the electrodes were starting to get pretty thin, however.)

 

[EliteConcept]

heheh ok i was just checking? its sometimes hard to determine the context that ones statements should be read in...

 

[SQExplorer]

Hey Elite,
Good post. Were the wires the same size were bigger?

I would honestly like to see a comparison of diffrent brands..

Anyone with me?

 

[EliteConcept]

i thought they were 8mm but upon looking at the box to double check i didn't see that so i believe they were the same size.