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Ford recommends 87 octane in the owner's manual for my 5.4L '98 Ex XLT. What problems/concerns would there be with bumping up to 89 or even 92 octane? I know the owner's manual is explicit about using ONLY 87 octane in my wife's '01 Mustang w/3.8L V6. The owner's manual states that it will cause poor performance and most likely will cause it to throw a check engine light.
Thoughts?
Thoughts?