The ECU switches to low-octane mode when the knock sensor detects a certain amount of knock over time. When a single cylinder knock event is detected, the ECU pulls 1.2 degrees of timing (aka the Knock Retard). Once the average KR hits -8 degrees, the ECU switches to the low-octane maps until the vehicle is restarted. In the Z32, the high-octane maps are actually for Japanese 98 RON, which equates to ~94 in North American octanes (A.K.I. or RON+MON/2); so there is pretty much always going to be some Knock Retard with our fuel.
