Hi all,

I have a forged and mapped 2007 STi Spec D.
I'm just curious about something...I have a PSi3 in the car, and KC is one of the live readings it gives me. Thing is, I know nothing about what knock correction actually is or what it means.

Seems to be 0.0 when cruising, then when accelerating, it looks like it fluctuates...perhaps to 1.5 or 2.5, I'm guessing it varies with how hard you accelerate?
I never go WOT, but what is knock correction exactly? What's a good reading reading?

Then there's AFR - air fuel ratio, but what's a good reading on that?
It could well be that all cars are totally different depending on the map etc, but there must be a decent ballpark figure?


Many Thanks,

 

AFR explained

 

Afr should generally be as close to 14.7 as possible at idle, some fluctuation is OK, for instance mine will sit around 14.7 the majority of the time but occasionally fluctuate between 14.3-15 for a split second then settle again. Afr should be around 11.something (I forget) under wot, anything above 10 is generally OK but lower can cause borewash, most say mid 11s is best so as long as they are close I wouldn't worry.

As to knock readings I've seen it said that if it's under - 2.8 and low load it's likely false knock from external sources, transmission, loose objects in the bay, pops and bangs can all cause false knock. I get it occasionally, in all 3 scoobys I've had btssm will occasionally show flkc at - 2.11 but it's always at low load and little to no boost, never have I seen it occur above 0psi . If your getting knock correction under heavy loads or wot I'd definatley have it checked. If not I wouldn't worry personally but the only way to know for sure is a pair of det cans or taking it to a mapper to check over who would use det cans anyway.

 

IIRC, the knock correction on 32-bit ECUs should be displaying 1.0 if there is no knock detected.
Negative values means knock has been detected and the ECU removes ignition advance.