MolaKule
Staff member
It depends on type of wire, whether it is solid core or RF suppression.
RF suppression wire is approximately 850 ohms per foot.
RF suppression wire is approximately 850 ohms per foot.
spark plug wire ohm readings
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A service manual should have that info for your specific vehicle. Longer wires will have more resistance. It's usually specified as resistance per foot of wire.
I've only checked wire resistance once. I didn't know how old they were (at least 100,000km, car had 300,000km) and I was doing plugs, so I did wires too. If I remember correctly, the old wires ranged from 3kohm to 9kohm, and were not all from the same manufacturer. I was surprised when the new ones measured much higher (something like 8kohm to 15kohm). I put them on and the car ran fine, just as before.
I've only checked wire resistance once. I didn't know how old they were (at least 100,000km, car had 300,000km) and I was doing plugs, so I did wires too. If I remember correctly, the old wires ranged from 3kohm to 9kohm, and were not all from the same manufacturer. I was surprised when the new ones measured much higher (something like 8kohm to 15kohm). I put them on and the car ran fine, just as before.
MolaKule
Staff member
The number I gave was for new wires and cold.
age is a factor with plug wires too. Ohms spec doesnt really reflect the loss bled out of the wires from broken down insulation. Look under the hood some night, if you see blue sparks running out of the plug wires or the car mis fires in damp weather then replace the wires. I couldnt believe the difference a new set made after 250k miles on the old ones.
exactly. In fact, I've measured wires that "leaked" like this and often found them to be perfectly within spec. But bad nonetheless.
250k on one set?
With newer wire conductor technologies, I believe the insulation is now the weak link; it is more likely to break down (causing the arcing you mention) than the actual conductor to show an open/hi ohm circuit.
Anything over 6,000 ohms is no good.
I just replaced a 7 year old set on my truck. It has been running crappy all summer, and I decided it was close enough to fall to tune it up. I put so few miles on it, I have been running the points and plugs 2-3 years. New plugs didn't do much, only about 7 K on AC's. However, I noticed a lot of rust on the terminals. The wire terminals were badly rusted. I could have made more effort on cleaning or maybe you can even still buy separate terminals, but figured the 7 year old rubber wasn't worth it. A new set made a big difference. Checked with a magnet, and they have brass plated steel too. Is this what I get for buying cheap ones?
The new ones are from AAP. The old ones were Wells from Wal-Mart. My Wally's has crap compared to what they used to. No AC plugs, just AutoLite, Champion and Bosch. AAP wanted twice the buck a piece last time at Wal-Mart for AC's. No wires at all. They didn't list any for my LUV last time, but I poked around and found a set that worked, I think a MB application. Nobody had wires out where I could look at them, or stocked anything listed for my truck. Had to order them.
I prefer to replace stuff before it hurts performance or fails. May even buy a new truck someday.
The new ones are from AAP. The old ones were Wells from Wal-Mart. My Wally's has crap compared to what they used to. No AC plugs, just AutoLite, Champion and Bosch. AAP wanted twice the buck a piece last time at Wal-Mart for AC's. No wires at all. They didn't list any for my LUV last time, but I poked around and found a set that worked, I think a MB application. Nobody had wires out where I could look at them, or stocked anything listed for my truck. Had to order them.
I prefer to replace stuff before it hurts performance or fails. May even buy a new truck someday.
you're not the only one. i tested mine to see if i could use a replacment. i got around 8k per 3 feet, roughly. 85k miles on NGK wires that look only months old.
my chilton manual states no more than 16 kohms per 3.28 feet. i'm gonna leave 'em on a little longer.
my chilton manual states no more than 16 kohms per 3.28 feet. i'm gonna leave 'em on a little longer.
I think the wires are no more than 1.5ft, probably 1.75ft for the longest. I figured the low two was good reading. These may be the originals, they came off of the motor that had 90k according to the odo, may have only 45-50k on them though. It does run better but still bogs down before it warms up.
This is very true. Voltage loss through crossfiring can be much more than what's lost through high resistance. The thing is, once a spark finds it's way through a crack in a wire, it'll continue 'shorting', and get worse. It's most apparent when going up hills and in high load situations.
I wish the Wal-mart's near me carried plug wires, period. They haven't stocked any in about four years, and I used the Wells quite a bit. Also, they used to stock regular Champion plugs and now just the lawn mower/marine plugs. I miss the AC's too. Kinda sucks the Delco's I used to buy for 3.00/two pack now cost 3.00 apiece at Advance.
Does anyone know what spark plug wires are supposed to read? The ones I just pulled off the car 2 at 4-5k, one 9k, and the last at 15k. I guessing the last two are little high. I could test the new ones but I tested the old ones after I got the new ones setup perfectly. Then again they're a different brand so that may not be a good base reading. Or am I the only one bored enough to test spark plug wires??
JHZR2
Staff member
I didnt see sparks, per se... I saw bright spots on the wires as the engine ran.
TO be totally fair, the MSD wires that I put on did very much the same thing, especially at the end connectors! From new!
JMH
TO be totally fair, the MSD wires that I put on did very much the same thing, especially at the end connectors! From new!
JMH
really? strange indeed.
the bright spot is probably a corona and it's a precursor to sparking. Corona breaks down the insulation. Not good on new wires (if that's what it is, and i cannnot imagine what else it could be other than corona)
the bright spot is probably a corona and it's a precursor to sparking. Corona breaks down the insulation. Not good on new wires (if that's what it is, and i cannnot imagine what else it could be other than corona)
JHZR2
Staff member
This sounds right...
I checked the OE GM wires on my 98 ZR2, as in the dark I could see a little bit of 'brightening' of the wires.
Each one was more or less 1500 ohms.
I replaced them with MSD wires, they were SIGNIFICANTLY lower... Cant recall the number, but it was very low.
No issues with RF, etc.
JMH
JHZR2
Staff member
oh... this was on my GM 4.3L V6
Thanks!
JMH
Thanks!
JMH
I've never seen any sparks, touched a wire or two that shocked. The wire that was the worse, was the the number one spark plug wire. I just set the timing, should I recheck it, it's rather a pain in the butt.
Not so. There is a lot more than just seeing the spark. What about when the engine is under full load? What will be the quality of the spark then? An oscilloscope will show you how well of a job the ignition doing firing each cylinder.
yes so.
my point is that if it is leaking sparks (ie voltage), it cannot be delivering the full voltage to the plug.
No sparks does not mean it's good (which I did not say), but visible sparks coming thru the insulation (my point) is bad and the fact that the resistance measures OK is moot.
If it is leaking at idle, it will certainly be leaking more at load.
my point is that if it is leaking sparks (ie voltage), it cannot be delivering the full voltage to the plug.
No sparks does not mean it's good (which I did not say), but visible sparks coming thru the insulation (my point) is bad and the fact that the resistance measures OK is moot.
If it is leaking at idle, it will certainly be leaking more at load.
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