Just filled up the tank with 91 octane premium fuel

[TheSilkySmooth]

Originally Posted by 07WYarisRS

our engines are NOT high compression... my street bikes run 200psi plug per cylinder and run on 87 octane... guess what they have less then 10:1 compression ration.

The ECU will not re-tune for higher octane...
The only time it will make a difference is if the engine is knocking... then the knock sesor will pick up the engine knock and retard the timing.. it won't change the fuel maps to compensate.

Spark knock AKA PING is completely normal and just means the engine is running efficiently...

running a lower octane fuel will reduce carbon built up as it has a lower flash point and will burn more efficiently and completely... Also start running a TRUE synthetic like Amsoil or Redline with no mineral oil or by products that cause deposits to form and after 10 years you engine will still be 95% carbon free

So 10:1 in the Yaris is NOT high compression? BAH! 2) The ECU is CONSTANTLY adjusting the fuel trim for proper running as required!
3) How do you know if the timing is in retard (without a scan guage) on WOT?

All that said, I usually run regular. If the engine is healthy, and NOT carboned up, it should run OK on 87PON. I think I cooked my cat#1 from driving too hard and have to get it replaced with the high flow ( for free!?) on the TSB EGO35-06 .... Car is feeling lazy and getting choking sulphur smell in the cabin when I whomp on it