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False knock or actually knock?

Practical Reflash Tuning

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Hello,

So I'm pretty much stuck at this point. I have knock accuring on cylinder 2, already at 0.5 bar, which my plex knock moitor says it has high peak, and I also can hear through it with headset, I'm using 10k hp filter on the Plex knock monitor software

My setup:

Civic 97

B18c sleeved and forged internals

Around 10.5 compression ratio

Head has a custom porting job

Custom Camshaft(also tried OEM integra type r cams)

Supertech valve train

Custom turbo kit(T4 divided top mount style) with pulsar G40-1150)

Fuel: EU 98 octane + water/meth(direct port injection)

Hondata S300

Background:

So my car is 97' Civic which has almost all of the supporting mods with an almost bullletproof engine. The head is custom ported with a custom cams. Whole engine was assembled at "engine" shop. I made turbo kit by my self. T4 divided manifold, 4" downpipe, 3" intercooler piping. G40 turbo, so its a big non restrictive turbo.

Knock sensor location is stock, which is on cylinder 2.

What I have tried so far:

Checked the injectors(ID1700x), which was as good as it can be on flow test

Switched coil packs, still knock on cylinder 2

Changed spark plugs, running Iridium 8's

AFR is stable through around 10.8-11.5. Tried to add more fuel without any change.

Checked timing ECU to real

Checked timing belt

Added extra ground to engine

Double checked my map

Tried all the way to -2 degree of timing

Knock is the same if its 0.5 bar or 1 bar boost pressure

Car runs great without any hesitation

Checked cylinder 2 with a endoscope camera and it looks fine

Thought the custom cams did cause trouble, so I tested OEM Integra type r cam. No change.

Any idea what can be the problem here?

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There are two ways to figure out if it's false knock or real- retard ignition timing 6-7 degrees or increase fuel octane rating (can be some additives like HKS octane booster or ethanol). If knock is still there check calibration of cnock detection unit or find a mechanical issue that creates the noise which is determined as knock - in many cases it would be rocking clutch or some other metal-to-metal contact.

1.) Are you using the correct bore diameter on the Plex to get the correct center knock frequency?

2.) Use the knock mode 2 for 2nd harmonic frequency

3.) Make sure your signal gain is set such that the peak noise level you get at high rpm is between 80-100

4.) Try back the 10k high pass audio filter with the second harmonic center frequency as well as the closest band pass filter to the 1st order harmonic center frequency...the 10k high pass does not work well on all engines and can give sounds that sound like knock but isn't.

1. Yes, I use 80mm bore diameter. My block is 81mm

2. I use the 2nd harmonic frequency

3. to make that, I need to set sensor gain to lowest possible in the computer software. Will that be correct?

4. I didn’t understand this, what setting do you recommend me to try? I use the computer software from Plex.

1.) Try 85mm see if that makes any difference

2.) Ok

3.) Yes that's ok

4.) I am referring to the audio filters. You said you were using the 10k HP filter. Example If your first order knock frequency is 7000khz try using the 7k band pass audio filter. If it is 8000khz use the 8k band pass audio filter

Wow, so the bandpass filter 7k “fixed” the issues!

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The 7k bandpass should not affect anything on the laptop noise profile though, that only affects what you hear via the headphones. It is an audio filter.

What would change the signal profile on laptop is signal gain, knock freq, knock mode.

Fyi your gain looks a bit too low...I can't see the numbers on the axis but it looks that way. Adjust the gain to get the peak levels at high rpm between 80-100

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