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Ignition wire resistance and knock sensor resistance?


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3 replies to this topic

#1 Suby Skier

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Posted 15 March 2007 - 07:12 PM

I have a 99 Outback Wagon, 2.5. 148,000 miles.
Does anyone know what the resistance should be on the spark plug wires I am getting a range from about 8 ohms - 11, is this normal?
Also what should the resistance be on a knock sensor?
Thanks in advance.

Ken

#2 OB99W

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Posted 15 March 2007 - 07:56 PM

[...]Does anyone know what the resistance should be on the spark plug wires I am getting a range from about 8 ohms - 11, is this normal?

Assuming the unit is actually kohms, yes.


Also what should the resistance be on a knock sensor?[...]

The knock sensor is a ceramic piezoelectric element; expect resistance to measure quite high. However, resistance testing generally won't tell you much about condition of the knock sensor -- they often crack when failed, so check visually for that, or just replace if you have strong reason to suspect it. If replacing, be sure to clean the mounting surface and tighten the bolt to the proper torque.

#3 Suby Skier

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Posted 15 March 2007 - 08:07 PM

I lower resistance numbers better. I also have a 97 Outback Sport and I checked those wires and got from 6.35k - 8.35k ohms?
When should you replace the spark plug wires? My vehicles have 176,000 and 149,000 on the 99 Outback I do not think that they have been changed before.

#4 OB99W

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Posted 15 March 2007 - 08:48 PM

I lower resistance numbers better. I also have a 97 Outback Sport and I checked those wires and got from 6.35k - 8.35k ohms?

The resistance measurements you're reporting are reasonable. There has to be a certain amount of resistance in the secondary ignition circuit. It's needed to minimize RFI (Radio Frequency Interference), which can effect operation of electronic equipment in the car (computers, radio, etc.); by limiting the rise time of the spark, it can also somewhat improve ignition by lengthening the firing time a bit.

When should you replace the spark plug wires? My vehicles have 176,000 and 149,000 on the 99 Outback I do not think that they have been changed before.

Although plug wires can last for many years and miles, those are a lot of miles for even the best wires, and you might consider replacing them. Nevertheless, if the resistance measures okay, and the insulation is in good condition (no visible sparks when inspected in the dark, and no misfiring, etc. if wetted down by road splash or lightly misted with water from a spray bottle), then they may still be usable.




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