N62 minimum valve lift

[cmyachtie]

Originally Posted by bcredliner

I know of no science that would explain how lower octane fuel might/will solve a stumbling problem making me a skeptic looking for the logic.

The basics of octane differences are that lower octane in a high compression engine where the manual calls for high octane will likely lose performance if the timing adjusts or spark knock if the engine does not have the capability or range to do so. Higher octane in a low compression engine calling for low octane will have have little effect on anything making it a waste of money for the extra cost. Stumbling cure or cause is not a part of either change.

The only long shot exceptions that I can think of is a change in the source of fuel such as trash gas to name brand gas, changing to a fuel that contains a fuel system cleaner, you are in a state where they have different additives for summer than winter that your engine doesn't like or, perhaps, something else that is causing the stumbling that using lower octane fuel is masking.

What vehicle are you referencing and what octane is recommended by the manual? What do you mean by "mostly" 89 octane? When in this scenario did you add injector cleaner? Were you always running Esso gasoline? How long had you had the stumbling issue? Have you done anything other than change octane shortly before or during this timeframe?

I am just as puzzled as you are ,having suffered from these random misfires sinceI got this car for 5 yrs now and only in winter, always run Esso 91 octane which is recommended by BMW for the 545i N62 engine(Esso here in my neck of the woods is my best choice available and have run this in all my previous BMW's for over 15 yrs now)
As far as lack of performance goes, only thing I have noticed is a delay in response when flooring the gas pedal, driving wise nothing noticeable but maybe better mileage (is still early days on that observation).
My last four fill ups have been one at 87 and three at 89 so there was a mix there when switch occurred, but now it would be straight 89 for the last two weeks or so.

Kudos to fasteddie for the suggestion, much appreciated!!!