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Plex Knock Monitor V2 Engine Noise Profile

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I recently purchased a Plex Knock Monitor V2 to try to see exactly what is going on regarding some reported knock by the factory ECU and knock sensor.

The vehicle in question is a 2017 Honda Civic Si 1.5T. A new engine has been installed with upgraded rods, pistons, and valve springs / retainers. A larger, aftermarket turbocharger has also been installed. I am working with another tune (with much more experience than myself) and we have determined the ECU is reporting knock under circumstances that should not be close to inducing any knock.

I've recorded a few runs with the Plex system and the noise profile (based on the PC software chart) is not what I expected it to be. I expected a more gradual increase in noise but for some reason around 5600 RPM it tends to go all over the place. There does not seem to be much data online for me to compare this to so I am reaching out to the community hoping you can help me make some sense of this. I will attach a screenshot from each of the three runs, labeled as follows:

12- This is a 12psi pull where ignition was heavily pulled because I did not have the factory knock sensor attached and the ECU was not happy about it.

12+ This is a 12psi pull with full ignition advance (peak advance approximately 12 degrees) The factory ECU/sensor reported this run as clean, no knock.

22+ This is a 22psi pull with full ignition advance (peak advance approximately 8 degrees) The factory ECU/sensor reported this run as clean, no knock.

25* This is a 25psi pull with full ignition advance (peak advance approximately 5 degrees) The factory ECU/sensor reported knock on this run at approximately 4600 and 5300 RPM so I ended the run early

25 This is a 25psi pull with full ignition advance (peak advance approximately 6.5 degrees) The factory ECU/sensor reported knock on this run at approximately 6200 and 6500 RPM. I did not end the run early because I wanted to record the full range with the Plex monitor.

I am running a fuel blend of 93 octane and E85, to achieve an ethanol content of approximately 30%. I should be able to comfortably achieve about 26psi with 9-10 degrees of ignition advance with my current setup but the factory ECU is not happy when I do.

Any input is appreciated. Thanks

Attached Files

You should tap and input the ignition 1 signal into the Plex, then you will be able to see the knock levels per cylinder. You may have a particular cylinder or two that are way noisier than the others.

Unfortunately, the Plex V2 does not have individual cylinder gain adjustment, which is a big drawback IMO. The high end systems like Emtron and Motec M1 offer individual cylinder gain so you can quiet down certain cylinders.

Are you using the first or second harmonic frequency?

Thanks for the reply.

I initially tried to pick up IGN 1 by using an inductive clamp over the factory "service loop" that I typically use for the RPM pickup on my dyno. When that gave me inconsistent results, I tried to directly connect the red and black wires in the service loop to the trigger tires for the Plex unit, but I didn't pickup anything with that. I then went and just tapped a tach signal wire. I do see the benefits of picking up IGN1, I'm just not sure how best to grab it at this point with the factory ECU in place.

The Motec system for the 2017+ Civic Si is nice, but I'm sure you are already familiar with the price tag. :)

I am monitoring on the second harmonic frequency, at the "75mm" level. My pistons are 73.5mm. I'm listening to audio using the Bandpass 7KHz setting but I've not really gotten far enough with it to tell if that is any good or not. I can barely hear the audio monitor with the ear buds during a WOT pull with a very mild exhaust system on the car, I may need to put a set of earmuffs over them to better hear things .

The IGN1 wire is pink and is located at pin E37 of the OEM ECU.

You can turn up the pre-amp dB in the software if the volume is too low.

Attached Files

Thanks for the tip on IGN1, I had a feeling you would know where to find it.

Also a great tip on increasing the volume. I saw that setting but did not realize what it was for.

I will get hooked up on IGN1. Maybe the individual cylinder data will help me better understand what is going on.

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