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post #1 of (permalink) Old 06-07-2002, 05:13 AM
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Spark plug wire resistance

I have the 8.5 mm Jacobs spark plug wires. I think I have one with a problem. What is the rule of thumb for measuring resistance to see if you have one gone bad? Is there a better way of testing? Is there a chart of resistance for different lengths of wire? I put the stock Motorcraft wire in place of the one I think is bad and I *think* it runs better. [img]images/icons/frown.gif[/img]
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post #2 of (permalink) Old 06-07-2002, 08:32 AM
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Re: Spark plug wire resistance

I have the jacobs as well. You should be measuring in the ballpark of 250 ohms resistance per foot of wire. If its off some not a big deal. All should measure roughly the same.
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post #3 of (permalink) Old 06-07-2002, 05:51 PM
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Re: Spark plug wire resistance

They's guaranteed for as long as you own your non-commercial vehicle

so I'd be asking them what the acceptable specs are and then nailing them for a new set if yours don't measure up anymore.

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post #4 of (permalink) Old 06-07-2002, 08:15 PM
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Re: Spark plug wire resistance

Whenever an engine feels like it's missing, just shut 'er down and start pulling plug wires one-by-one (starting it up after each pull). If it runs worse, the wire/sparkplug/cap terminal are good. If it runs the same, you've found the bad spot.
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post #5 of (permalink) Old 06-09-2002, 08:01 AM
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Re: Spark plug wire resistance

Well, I called them. They say it is 350 ohms per foot. I can always take one the same length that is believed to be good and measure it, I guess. Now I discovered that I need new batteries in my ohm meter.
post #6 of (permalink) Old 06-10-2002, 06:05 AM
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Re: Spark plug wire resistance

I put new batteries in the multimeter, zeroed the ohms and checked it against a new 1.5K resistor. It read 1.503. So far so good. 6 of 8 of the Jacobs wires read over the 350 ohms per foot in a range of +5 to +685 most were +30 or a 3% variation. Is anything over the 350 per foot acceptable?
post #7 of (permalink) Old 06-10-2002, 11:24 AM
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Re: Spark plug wire resistance

anything close is acceptable + or -. I would ask Jacobs about the +685 wire though. That might be one they warranty.
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post #8 of (permalink) Old 06-10-2002, 07:36 PM
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Re: Spark plug wire resistance

Jacobs is going to replace the wire that was way over. The others are within tolerance. The resistor I calibrated the ohm meter with is +-5%. We'll see how it comes out.
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