Knock Sensor Output Differences

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Knock Sensor Output Differences

Postby DavidBraley » Wed Jan 30, 2019 11:04 am

After a lot of searching, I'm having trouble finding an answer...

This question relates to the GM LS/Vortec 2000-2002 GenIII 0411 controlled V-8 engines.

I understand that knock sensors are engine specific. I've read that it has a lot to do with the cylinder bore of the block (something to do with the resonant frequency of that combination). I'm guess then this is why the knock sensors for the 5.7L, 6.0L, 7.4L, and 8.1L engines all use different knock sensor part numbers. I'm also reading that the internal resistance of the knock sensor is supposed to be something close between 93K-107K ohms (can't find if that ohm value applies to all of them, yet).

What I'm not finding is the difference between the output signals from those different knock sensors, and what the PCM does with it. And more specifically, is the bin file for each engine size somehow tied to it's specific knock sensor. So hopefully my next question makes sense. Sorry, but my "EFI" vocabulary is still a work in progress...

So the question I have is if I use a 6.0L bin file in a 0411 PCM to tune a 8.1L engine (with the correct 8.1L knock sensors in the block), will the 6.0L bin file in the 0411 PCM know how to properly handle the signal from the 8.1L knock sensors? I fully understand that the fuel and spark settings will be all wrong for the 8.1L, and I hope to change those to supply the fuel and ignition needs for this different size engine. What I'm concerned with is will the original 6.0L bin be able to correctly detect knock from the 8.1L knock sensors. (sorry or the repeat)

Why do I ask? I'm having a devil of a time finding a stock, unmolested 8.1L bin file that uses a 4L80e transmission. The two 0411 PCM's I have here with 8.1L bin files, and some other 8.1L bin files I was able to find on the net all use the Allison 1000 transmission. I'm guessing it will be impossible for me to get those bins to correctly control the the 4L80e. Unless there is a work-around for that problem...

I hope what I just asked made sense.

Thanks in advance for your thoughts on this.

David
-David

Horsepower determines the speed you hit the wall. Torque determines the size of the hole you make.

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Re: Knock Sensor Output Differences

Postby Charlescrown » Wed Jan 30, 2019 2:44 pm

Not my most knowledgeable area but the main difference with different bore sizes is the knock filtering. You'll probably find the ones you mention have different resistance values and can't interchange because the ECU would log a code.

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Re: Knock Sensor Output Differences

Postby pman92 » Wed Jan 30, 2019 3:59 pm

The sensors themselves are a piezo crystal. Movement/deformation of the piezo generates a voltage. So as the sensor is bolted into the block, tiny movement (vibration) of the block generates a voltage signal, like an audio signal, sort of like an AC voltage but with all different frequencies.

The voltage signal coming out of the sensor will be very raw and noisy. All sorts of things cause the sensor to generate voltage. The mechanical things moving around make noise. The valve train etc will all create part of the signal. Hit the engine with a hammer with the oscilliscope hooked up to the sensor and you will see it in the voltage trace.

Somewhere in the PCM something will filter the signal. It will remove all the unwanted frequencies. There is one specific frequency it is looking for that is knock. That specific frequency is very much related to bore diameter of that particular engine. Whether that's done in hardware or software in a '411 I couldn't tell you.

As for having different sensors, I'm also not sure why. They might have different resistances. Or maybe they are more reactive close to the frequency they are designed to pick up. All the different engines have different knock frequencies, so the sensor in them is designed to work best around that frequency
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Re: Knock Sensor Output Differences

Postby DavidBraley » Wed Jan 30, 2019 7:14 pm

Thanks for the replies.

I took a look in TunerPro RT, and there is a TON of knock sensor settings when reading a bin file. Tomorrow when I get some time, I will open up two instances of TunerPro, and compare those knock sensor setting between a 6.0L bin and a 8.1L bin I have here.

I'm guessing that the physical hardware in the 0411 PCM is the same, and the managing of the knock signal comes from these settings that make up part of the bin file. If that is the case, I should be able to copy over the 8.1L bin knock settings to the 6.0L bin knock settings. I think...

Thanks again for the help.

David
-David

Horsepower determines the speed you hit the wall. Torque determines the size of the hole you make.

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Re: Knock Sensor Output Differences

Postby DavidBraley » Thu Jan 31, 2019 4:06 am

I've had another potentially crazy thought.

Does anyone know here if it's possible to bring the 4L80e transmission bin settings in a 6.0L bin file, and write over the Allison settings in the 8.1L bin file? That might give me a much better starting point for this engine and trans combination from the get-go.

I wouldn't be surprised if other people do this already, so excuse my ignorance. :D

I need to get my engine run-in stand finished so I can physically try this stuff out.

David
-David

Horsepower determines the speed you hit the wall. Torque determines the size of the hole you make.

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