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Issues setting plex knock monitor on vtec bseries engine

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I've been away a while but I'm finally tuning my civic trackcar.

I'm having issues with the plex v2 being too sensitive(I'm 95% sure the engine isn't knocking) a few details on what I've done/learnt so far.

I have the sensor mounted on the intake manifold, ive seen tuners do this on my own car before and it's supposed to be the best spot for signal to noise ratio.?

Running a completely standard integra R on the monitor see it reading 120s with a sensor gain of 18.

For my engine to see 120s I need to turn gain down to 11 (lowest it will go)

I've tested the full rpm range with 12deg timing retarded over one of the basemaps in hondata(roughly 12deg at 8000 rpm) same result as running 21deg at 8000rpm. So it's not knocking at 12 as surely it would have gone bang at 21?

I know 12 is too low as I start getting boost creep when the timing is that low.

I'm using the basic preset settings on the plex of 80mm cylinders(mine are 81.5) and the gain low as it will go.

Through the head set I get what I can only describe as static at about 8k no matter what the timing is (12 or 21)

I'm concerned about inducing it on purpose as I may be missing the knock as it is and pushing the timing further whilst still not hearing it....

I guess I'm after advice on setting the plex up so that it's not flashing at me all the time lol

I have always heard that the knock sensor should be installed on the engine block and NOT on the engine head (or the intake manifold) to avoid valvetrain noise.

Hi Getuned

my thoughts on your post are:



--> mount the sensor(s) mid height or higher between the cylinders. No shortcut there. The quality of the data output depends on the quality of the data input. Rubbish IN = Rubbish OUT, apologies to be so blunt.


The OEM manufacturer did not attach them there when developing the engine for sure.


Best for saving time for the "tuner" (dabbler) only, yes.


I know 12 is too low as I start getting boost creep when the timing is that low.>>

Follow PLEX's guidelines, do safe runs on the dyno to gather the mechanical noise threshold line, noise profile. , mechanical noise increase will be quite predictable on higher power output under load, just adjust the PLEX's threshold line with a bit of a safety margin. If there is knock, you will find that you get isolated dots on the graph very high up. It is important to note that the ignition timing should not be overly conservative during these calibration runs because the mechanical noise WILL increase once the motor makes good power. Just stay away from an assumed MBT by ie. 10-12 degrees. What I am trying to say with this is to not retard the timing ridiculously for the sake of finding the mechanical noise profile.


The preset at 80mm is close enough. Play and elaborate with the second harmonic frequency (x2) and gather if you get a clearer signal with this setting.


mhh, I would not trust the gain nor any other setting if the input source is of questionable origin (intake manifold, valve cover, etc)


:GOTO TOP // this line is skipped

Thanks for the advice.

I have a spot I can use on the block that's around half way down and right of centre. I could try this spot against the spot on the intake....

I've not played with the plex settings too much as I'm using it via laptop power and don't have any signals to the plex (rpm etc) but I'll wire the loom in and see what I can learn about the noise profile. Having the 10khz high pass filter on seemed to help clear a good portion of the static noise.

This is the first engine I've tuned so I'm a little cautious to what conservative timing is, hence ending up pulling 12 degrees out trying to learn on the go.

Don't worry about sounding harsh or blunt, I'd much prefer that with something like this...

I'll be back later today with my results.

So I couldn't get the sensor in the stock location because I didn't have a 27mm deep socket to remove the old one. (On order)

I did however put it here to test the theory of the intake manifold being the problem.

Whilst I was there I got the rpm signal wired in and this is the noise profile I have with conservative ignition timing.

Eventually I'll get the sensor in the stock location but for now I'm quite happy to press on with the tuning in its current state.

We usually reply within 12hrs (often sooner)

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