Originally posted by Crespro
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This is the verbiage I've seen. As an engineer who worked in calibration, this language tells me that the truck is calibrated and certified to regular grade fuel since its advertised as such. Their strategy is revealed where they do not rely heavily on tables based on temperature to pull spark but rather rely on their knock control system. As a result, the ECU will only pull spark when knock occurs. And premium fuel has a higher knock index so high temperatures and heavy towing will deliver the same spark advance where premium fuel will lower the propensity of knock under those conditions.
Based on this information, non towing and cooler weather will work best on regular grade fuel and will save you some coin and maintain the advertised fuel economy or close to that number.
Jim
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