Octane and timing change

[JFO]

I'm curious about how our engines adjust the timing when octane level is changed from low to high. I understand how the ECU retards timing if it senses detonation or knock when a low octane fuel is used. If you switch back to a higher octane, say from 87 to 91, how does the ECU sense the change and re-set the timing? Or does it require a battery disconnect and new adaptive cycle?

Jim

[JDS60R]

It creeps up on it. The ECU will use demand for it to initiate the change the quickest. By accelerating it lets it hit the knock point and then takes measures to control it. It is always doing this and gets hints from the MAF and coolant temps sensor as well as the Oxygen sensors and boost sensors if equipped.

If you are light on the throttle the ECU is still trying to use the least amount of fuel before getting too lean or knocking.

[JFO]

So it is advancing to a knock and then retards at the point of sensing a knock? Makes sense.

Thanks...

[JDS60R]

Simply put - Yes
It can use fuel enrichment or timing. It has strategies that it knows works best in each situation (ie - a little more gas and a little less timing may work well in high heat low humidity while in high humidity the timing alone may work well) .