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Are all knock sensors melted?

 
Old 03-14-2018, 04:17 PM
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Default Are all knock sensors melted?

I'm building a 04 and sensor looked like it overheated and the epoxy type substance had driped out of it. Wanting to keep stock Mazda sensors I ordered a used one and it came in looking worse than the one it had. This happen to them? Are they still good??
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Old 03-14-2018, 04:45 PM
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Most. Yep still good
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Old 03-14-2018, 04:57 PM
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Sending it.....thx
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Old 03-14-2018, 05:05 PM
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Yes, same here. I though I had an oil leak in 2002 NB from somewhere until i found out it was resin leaking form the sensor.
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Old 03-14-2018, 08:56 PM
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Have been searching used sensors and keep asking about resin and they are all as you said already melted.
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Old 03-14-2018, 09:06 PM
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Is there a better alternative that's still compatible?
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Old 03-14-2018, 09:45 PM
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no
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Old 03-14-2018, 09:55 PM
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So long as neither lead is shorted to ground (via the housing), and the sensor element is still rigidly connected to it, I see no reason why a partially-melted sensor wouldn't continue to function.

In theory, you should be able to test it by whacking the intake manifold with a hammer while watching the pulley with a timing light. Never tried this myself.
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Old 03-15-2018, 08:31 PM
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Is there any other way to test with a meter ?
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Old 03-15-2018, 08:45 PM
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Not really. It's a piezoelectric sensor, so it's not like sticking an ohmmeter across it is going to do any good.

If you have access to an oscilloscope, you could measure the voltage across it (maybe 5-10mv/div) while you bang on it with a hammer.
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Old 03-15-2018, 09:03 PM
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would this procedure from FSM help to test ?
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Old 03-15-2018, 09:09 PM
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Originally Posted by stevos555 View Post
would this procedure from FSM help to test ?
Yes, that's exactly what I said a few posts ago, re: "So long as neither lead is shorted to ground (via the housing)..."

(OK, to be fair, they specified a resistance range and I didn't.)
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Old 03-15-2018, 09:17 PM
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AIUI, a knock sensor is basically a specialized microphone. I *think* this means you could do a basic function test by hooking it to the audio in on a PC, tapping it with a hammer while recording, and then play back the sound file to see if you can hear the "knocks".

(disclaimer: I'm a software guy, not a hardware one, so this might blow up your computer, set your house on fire, and trigger the collapse of the false vacuum thus ending the universe as we know it.)

--Ian
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Old 03-15-2018, 09:18 PM
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Originally Posted by codrus View Post
AIUI, a knock sensor is basically a specialized microphone.
This is correct.

And I kinda feel dumb for not thinking of the "plug it into a computer" test.
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Old 03-15-2018, 10:21 PM
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So if resistance checks out and only small amount of resin is gone, buying a used one may be ok it seems. The OEM sensors are ridiculously priced - $140 on Mazdacomp.
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Old 03-16-2018, 12:02 PM
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I pulled the water lines to the stock oil cooler/heater to stop from melting my knock sensors.
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Old 03-16-2018, 12:22 PM
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That got me thinking that a hose heat shield maybe a good idea to wrap around the oil cooler hose and maybe a spark plug boot over the knock sensor body to keep some heat off.
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Old 03-16-2018, 12:24 PM
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What’s the point of all that? Why waste time and effort fixing a nonexistent problem?
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Old 03-16-2018, 12:29 PM
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So just let it melt?
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Old 03-16-2018, 12:38 PM
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the sensor will not melt. the dollop of resin that does melt is the stuff that simply holds the wire in place. Have you ever even looked at the sensor in person?

I know you're enthusiastic about wrenching on your car, and that's good, but it seems like you're just jumping into topics completely clueless and starting conversations about fixing problems that are just not there instead of focusing on issues that actually need attention.

So to re-cap: oem nb knock sensor is a perfectly good solution for knock detection on our cars. Nothing "better" needed. The resin melting doesn't affect anything or you'd see hundreds of people replacing their knock sensors every 5 years and/or complaining about it.

So basically, this is not a problem
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