I have a 2001 5.4L F250 S/D and the manual says to use 87 Octane fuel. I am wondering what the benefits to using 89 or higher are? It says in the manual that a higher octane will magnify rough idle; why?

 

[font size="1" color="#FF0000"]LAST EDITED ON 10-Jul-01 AT 01:51 PM (EST)[/font][p]I normally use 87 except for when I'm towing at less than 3,000 ft elevation, and then I use 89. Did the same with my '97F-150 w/5.4L. It seems the higher octane would allow the timing for the hot engine to advance a bit further than it otherwise would, and the additional power allows the transmission to stay in OD longer. Fuel economy while towing improves by about 1-1/2 mpg as well. Lower air pressure above 3,000 ft negates the improvement offered by the 89 octane gas.

crewzer - Y2K F-250 4X2 CC SB XLT 5.4LV8 AT 4.10LS TTPkg