MVS Forums Member huzzsaba:
Recently on a road trip, I filled up like I usually do at Canadian tire and got decent gas mileage that I usually get which is around 22 mpg. On the way back, I had to fill up at shell because there was no Canadian tire around, and I got the worst gas mileage in a long time which was around 18 mpg. It also felt like the car did not want to pick up speed.
Q: Do our cars get used to one brand of fuel?
Volvoninja jimmy57 explains:
Every drop of fuel is a new world.
The engine control module (ECM) gets input from oxygen sensors and from the knock sensors that are info that has to do with fuel burn. If the fuel is higher in ethanol then the O2 sensor gives a leaner indication and the ECM adds fuel to get the input from O2 sensor within proper range. If the fuel is low octane (who polices octane of fuel against what is posted on pump?) then the ECM retards timing and then undoes the change to test for knock again. After a few knock “tests” that show high tendency for knock the ECM will adapt timing cylinder by cylinder until the level is found where knock is nil. This adaptive is load range dependent and is not long term. Periodically the ECM will tet for knock and will return to normal ignition mapping when knock is not longer present.