Quote:
Originally Posted by rice_classic
I know. The ECU has no way of measuring or knowing the AKI rating of the fuel.
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Okay, so I think it is time for some education.
Every OBD2 ECU has the ability to track fuel octane. The ECU has a minimum of two fuel maps, High octane and Low octane. Based off of the amount of knock present the ECU either raises the Octane count, or lowers it. What does this mean? Well fuel calculations are based off an interpolation between the two maps, for instance...
If a given load and RPM access a lookup cell in the high octane fuel map and it is calling for a 12.5 AFR, and the corresponding low octane fuel map calls for an 11.5 AFR, based on the octane rating (or more correctly the amount of knock over time the engine has witnessed) the actual cell maybe somewhere between the two, or it no knock has been detected 12.5, or consistent knock 11.5. Remember pulling timing isn't the only way to fight detonation, an increase in fuel lowers the cylinders temperature and decreases knock also. If you don't believe me go pick up a scan tool and log "Fuel Octane"....