Fine Knock Learn Question

Vehicle: 2017 Subaru WRX

Platform: FA20DIT (COBB Intake)

Query:

Hello! I understand that Fine Knock Learn (FKL) is a learned parameter in the ECU. However, I'm seeing increasing FKL activity at WOT after 5k RPM. This will happen even immediately after a re-flash when the ECU has not yet detected Feedback Knock of any kind. Does anyone know what could be causing this? I've seen this happen before when combustion temperatures are too high. Typically, lowering boost or adding fuel helps. However, not this time. Any insight would be greatly appreciated. I've attached a data log (.csv) of the issue occurring in case that would help. Thanks!

Hello pretty strange to have that level of fine knock at such low timing numbers it could be possible it is actual engine mechanical noise rather than knock if you add 2 deg of ignition does the knock/noise increase ?

Hey Ross! Thanks for the reply.

It’s possible. That being said, if I reduce the ignition timing by 2 degrees, it has no effect on the amount of FKL or the level of knock noise.

However from my understanding, typically with engine noise, we would see actual Feedback Knock as the sensors pick up the engine noise and react to it. In this case, there is little knock noise being registered. The ECU is just pulling timing preemptively.

I’ve seen this happen when tuning my own car and it seemed to be solved by either lowering the boost targets up top or by adding additional fuel up top. In both scenarios, we are cooling the combustion temperature. I have a feeling that FKL and combustion temperature may be related. However, I’m not sure how the ECU would measure combustion charge as there’s no parameter for measuring Exhaust Gas Temperature in the ECU.

Ultimately, I’m looking to see if anyone can shed insight and either confirm my hypothesis or help me understand a better solution.