What is Fine Knock Learning aka FKL?
Answer: Fine Knock Learn aka FKL is the learned knock by the ECU. If your driving down the street and hit a bump, turn on the AC, and or have an actual knock, the ECU will store that knock value at that RPM & Load. Below is a Timing table. As noted Load & RPM is your axis. If you were cruising at 2000 rpm and were in the loaded row of 0.91 and you had any type of knock(-2.81for this example) then the ECU would store that -2.81 knock that happened at the meeting place of 0.91 load and 2000 rpm. Which that cell has a red box around it.
Any time while driving and the car goes through that same Load & Rpm aka the red box above, the car will register -2.81. Please read the important facts below:
1) Even if your car is showing -2.81 FKL, that doesn't mean you are actually knocking. Remember, the ecu learned that knock event and stored it. Imaging hitting a bump and your car registering it as -1.41. It now stored in the ecu. Don't be worried if your car is still showing -1.41 while driving. If you're not hitting any more bumps then your car wouldn't be actually knocking, since the original knock event was caused by that bump in the road.
2) That Learned Knock can show on the AP any amount of times. Could be 1, 10, or 100 times.
3) That Learned Knock will unlearn itself over time. If the ECU doesn't see any knock that number will start to get lower towards 0. At times you will see positive knock and that's a good thing.
What type of Knock numbers can I see?
At Idle - You shouldn't see any knock at idle unless you have TGV codes and you push the throttle.
Normal Driving - Normally, knock at low loads(-10PSI to 5PSI) is not a big deal. People will see -1.41, -2.81, -3, -4 from time to time. These WRX Fa20 are super sensitive and can knock due to many different things which I will explain below. DAM drop can also be expected to drop.
At WOT - Ideally, you should not have a knock during WOT. The occasional -1.41 or -2.81 can happen from time to time, but I wouldn't worry unless it is happening all the time under WOT and or higher than -2.81.
What about the high knock values?
Some WRX FA20's will experience high knock values such as -7 or -9. 90% of the time, the user doesn't even see it happen or feel it and just sees it when they look at their Accessport and then they freak out. Unless this is happening all the time to where you actually see it happen, I wouldn't worry about it.
I normally tell customers to log it happening and most if not all can never catch it in a log.
What are some of the causes of knock?
As I said above, these FA20 WRX's are super knock sensitive. A lot of things can cause a knock on these cars.
CARBON BUILD UP ON VALVES
HARNESS PLUGS IN THE ENGINE BAY NOT ZIPPED TIED
ANYTHING LOOSE IN THE ENGINE BAY
BUMPS IN THE ROAD
TURNING ON THE AC