Plex V3 Threshold Setup Help

Hi,

I'm new to the tuning world and my first project is a Ford Transit Connect running a 2.0 Zetec turbo & Maxxecu.

Following the courses on here I've got the van running on a decent base map while running the freshly built engine in. I've setup pretty much everything and have been pretty happy with the drivability without going for full power just yet.

My concern has always been knock, I'm happy and confident with my fuelling etc but want to start pushing for more power on the dyno so I have purchased a Plex Knock Monitor V3 but I'm not sure if I'm getting the setup right or of I'm actually getting knock.

The spec is:

2l Blacktop Zetec

Forged pistons & rods 7.7:1 Cr

GTX3076R turbo

Deca 875cc injectors

Full 3" exhaust

When setting up the Plex listening to the audio with in ear headphones and ear defenders as Andre recommends I'm hearing audio clear but I don't seem to be hearing anything that sounds like the samples of knock I've heard, it's very noisy even with the high-pass 10khz filter it's pretty noisy and I don't hear (with my novice ears) anything I think is knock however when setting the threshold the plotted data on thr graph looks like its knocking and Plex is logging knocks too. This is using a sensor gain of 8db.

I want to be confident in the knock detection before I move forward but I'm unsure where to go from here. I've tried holding steady stating and increasing the advance slowly to 40deg at 2500rpm & 120kpa load to try and give me an example of the knock sound on this engine but I can't hear that anything is physically changing.

I've watched the plex setup videos multiple times but they cover the V2 and the V3 configuration is completely different, it talks about the 2nd harmonic frequency which the V3 doesnt seem to have an option for. I've read the manual christ knows how many times and believe that I've set everything up properly but the data and my ears don't seem to tally up. Can anyone point me in the right direction so I can be confident and progress with my tuning?

I have attached an image of the noise plot in plex, I don't think I picked up any knock in the headphones.

Thanks in advance.

Rich

Edit: Also worth mentioning that the knock sensor is mounted to the OEM location on the rear of the block near the head in the centre. The surface was covered in paint but was cleaned up by lightly sanding back to the machined surface.

I've not used that unit so I don't have unit specific suggestions, but can you select a frequency double what's calculated for your bore size?

Hi Mike,

Thanks for your reply, it doesn't seem like it's possible. That's what's causing me confusion, for all the V2 guides people mention to try using the 2nd harmonic frequency but in the V3 I can't find this option anywhere, nor is it in the manual. I've tried to manually type in the frequency and it just changes the bore size massively so not sure if this will negatively effect my results.

This is the data being plotted in plex when trying to setup a threshold. I don't think that I can hear any knock in the headphones but the graph looks very noisy.

Hello Richard,

When the setup of the Knock detection system is not done correctly the V3 reports Knock even when there is no knock occurring(via audio Signal).

The best way for Setup is to listen for knock audibly while forcing the engine into some light knock.

After that analysing the recorded data and adjusting the Knock detection Parameters(Knock Frequency, Sensor Gain, Knock Threshold,...).

It could be difficult(or not possible) to force the engine into knock under your conditions(2500rpm & 120kpa).

You could try to use a lower grade fuel for testing purpose. Maybe try it in steady state @ 3000rpm + 140kpa.

Use safe Ignition values exept the 140kpa cell, try 45deg in this cell so you can adjust the ignition timing by pressing the throttle.

Once knock is occurring the audio sound(klicking) is obvious.

I had contact with Plex tech support (Ioannis Andrianakis) and he have send me some helpfull information please see below.

Before you analyse the data you should setup the page in the PDA like described in the help section.

Noise caused from knock is not consistent (not repeating frequently)

look if the noise appear in the expected frequencies

look for significant spikes in the "Signal" values.

look for spikes in the "Signal Range"(raw) values. (this is not always a clear indication but in most cases it correlates with knock)

High power engines with forged pistons are usually very noisy when operated at low rpm, low load

With the spectrogram you want to look where you have high intensity areas and and low noise.

High pass filter typically make it easier to detect knock audibly

The audio filter setting in the device configuration only affect the output through the headphones. The Data log file is not affected by this filter.

The knock detection frequency setting does not affect the audio from the headphones or in the pc.

Some improvements coming soon is the ability to set dual frequencies for detection as well as high pass and L/R channel selection for the audio in the pc software.

I have attached a demo file with clear knock provided from Plex and one that i have recorded.

On my file (EVO) the knock detection was not done correctly it was only for audio and signal analysing.

I hope these informations help you to get more confident with the device.

Hi Marian,

Just want to thank you for your help with this, I'm confident in the plex now after following your info.

Doesn't seem that my engine is very knock limited, only experienced light knock at 6k Rpm, 170kpa, 21deg, 0.84 lambda.

Managed to get the threshold setup properly and the audio pretty clear.

I find the audio very difficult to hear when on the dyno with the output set at the maximum 24db. Being new to tuning when adding timing I've logged the run and then listened to it back in the office, I find checking the data in the log with the audio gives me clarity.

Thanks again!

Hi Marian,

Would you mind having a listen to my log file I've just done and giving me your feedback on the audio & the data.

The log records 4 knocks but I think i hear a couple more just past 5k so maybe I need to work on the threshold.

Many Thanks

Rich

Hello Richard,

i have listened to your log file multiple times and i think there is no knock occurring(it sounds not like knock) at all.

Also in the Spectrogram there are no signs for knock.

Because i am not very experienced with the device i would recommend that you send the file also to the Plex tech support (Ioannis Andrianakis) info@plex-tuning.com

Ioannis has helped me with my file and gave me very helpfull informations.

Could you please share the informations you receive from the support because it helps speeding up my learning also.