Car: 1988 760GLE, B280E, LH-jetronic 2.2, EZ115K ignition system.

I was wondering if anyone could tell me how the anti-knock system on
my 760 actually work... I mean, what does it do when one of the knock
sensors detect knocking?

I would have thought that the ECU would retard the timing for the
knocking cylinder a bit, and then gradually advance untill "correct"
timing was reached or knocking was again detected - but maybe I'm wrong?

The reason I suddenly started wondering about this peculiar issue is this:

Early this morning, on my way to work, I had to stop for gas. Beeing early, I was obviously not fully awake, and filled up with 98 octane. Never done that before, always have run the 760 on 95 octane.

After a few minutes of driving, I noticed a change in the car. The "shudder" at 1900 rpm at moderate load had vanished. Completely gone! I've been
trying to locate the source for this vibration for a long time, without
success.

Could it be that I had a knock-situation at 1900 rpm, which the anti-knock- system has compensated for, thus making the engine run rough at this
particluar rpm? Remember, the B280E has a relatively high compression ratio of 10:1...

Best regards

-Tore