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Plex Knock Monitor V3 setup for Audio knock detection

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i am starting to work with the audio knock detection of the Plex Knock monitor V3.

It´s difficult for me to exactly differ between normal background noise and real knock events.

The V3 Knock detection and Audio output Parameters were configured as recommended for starting by the help manual.

The test car on the dyno is a modified Mitsubishi EVO 8 (engine with forged internals 86mm bore).

Test conditions: steady state 2500rpm, MAP 20kpa(gauge pressure), Ignition advanced from 13 to 20 degrees to push the engine into light knock.

Because it's realy noisy i have tryed to reduce the Sensor Gain value and change the Audio outut filter. Also i have tryed the second knock harmonic frequency (13600Hz) but i still have problems to detect if the engine is knocking or not.

When the ignition angle were advanced from 13 to 20 degrees a rattling sound is occurring but no clicking sound.

I have recorded and attached some logfiles from the same condition with different settings(Sensor Gain value, Audio outut filter, Knock frequency).

Please listen at the audio sound files and give me some feedback about the settings and if this is knock or not.

Thank you for your help.

Attached Files

I doubt you going to be anywhere near knock with 20deg at 20kpa MGP. I would expect it would need more like double that.

If you have a dyno that can hold RPM steady state, then one trick you can do is put a very high advance value in a single cell in the ignition table at the RPM you are holding at. So as an example based on your original test: Put 50deg advance in your 2500RPM, 20Kpa cell. In the cell below it (say 0kpa,2500RPM) you have a normal advance value. With the dyno holding RPM at 2500, you can then control advance with your throttle, press the throttle down more and more until you hear knock.

Try to carefully creep up to light detonation using a lower octane fuel.

This will make it much easier to learn how true knock sounds and to distinguish normal mechanical noise from real detonation. Once you heard it, it will become obvious.

Hello Guys,

thank you for your help / informations and recommendations.

I have done some testing based on your suggestions and knock were audible clear detected.

A Data Log file is attached.

Have you some recommendations and tricks for setting up the audio configuration very quickly and efficient on the V3 device?

Attached Files


Where exactly is the sensor mounted?

Hello Dominique,

the Knock Sensor is bolted to the engine Block on the OEM position (=middle of the block and close to the deck surface).

The surface is also perfectly flat.

Hi Marian,

Did you manage to get the Plex V3 setup so that you were confident in the data logs and also clarity over the audio?

I have just got the Plex but I'm also struggling to identify knock that Plex is logging and I'm starting to think it's something I have done wrong with the setup.

Hi Richard,

I am confident with the initial Setup proceedure with the device but i have not worked very much with it in the last months.

I will answer you on your post with my suggestions and Informations i have already gained.

Brilliant, any pointers would be greatly appreciated!

I'm itching to push on with the project but I'm not the sort to rush into something unless I'm confident I'm doing it properly.

Plex will never be getting my money again, the V2 was complete garbage. Mine constantly powers off abruptly, Lags behind on the software. It's now an expensive paper weight.

Tuner Nerd knock monitor pro, that is all. Makes you see how over priced those plex devices are

Hi Chris,

I've also got the tuner nerd and had nothing but issues with it. The features are great and it's definitely got potential but the software was far too buggy.

After speaking with them I tried everything they suggested but it was just so unpredictable, the software would crash out when detecting knock, the RPM would be stable some times and then other times really erratic so the data wasn't of any use.

After plenty of research I decided to go for the plex, despite the cost I wanted reliability which I'm hoping this will offer once setup correctly.

Which version of the TN did you have?

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