Just filled up the tank with 91 octane premium fuel

[07WYarisRS]

Originally Posted by TheSilkySmooth

if you have a CAI and open exhaust the ECU might retune over time for the higher octane and you might get some more torque, but I never found the need to add more than 2 gals to the rest of the tank in a mix to get all the octane the engine needs. try mixing in just 2 gals of 93 at a fill up of 87. Our engines are High compression and the eCU can start to retard timing when you get carbon buildup over time. A littel more octane can help. MAy car is starting to ping/knock at starting off in 1st gear at 20K miles on the odo. You dont drive hard enough to clean out this carbon, unless you run the car at WOT 3rd and 4th gear on the highway more than a couple minutes a day. That can clean it out. An melt your 2 layer exhaust pipe too!

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