91 octane corrects rough idle? - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 01-31-2010
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91 octane corrects rough idle?

So for the past 3 or 4 months I have been having a very rough idle. Yesterday I was completely out of gas and I luckly rolled into the station of fumes. I accidently pushed the 91 octane button instead of the 89. I caught it about the time the tank was half full. I said screw and just filled up the whole tank with 91.

Since then I have driven quite a bit since yesterday and the rough idle is gone. I dont really see why this would fix my rough idle. Was it just a coincidence or is there actually something to this?
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Old 01-31-2010
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Higher octane fuel has been known to help correct idling issues. So, no, it's not a coincidence.
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Old 01-31-2010
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Do you know why?

I thought that all higher octane did was allow the air/fuel to be compressed more with out pre-mature detination. I could be wrong though.
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Old 01-31-2010
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higher octane fuel also burns hotter so it could be burning any carbon deposits out that can cause rough idle
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Old 01-31-2010
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Ive been wanting to but 91 in mine but i cant afford it... haha
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Old 01-31-2010
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High Octane fuel burns slower and much smoother. In short, I would guess your rough idle is due to a timing issue.
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Old 01-31-2010
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Quote:
Originally Posted by ranger4.0 View Post
higher octane fuel also burns hotter so it could be burning any carbon deposits out that can cause rough idle
Agreed, could be this too.
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Old 01-31-2010
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all i know is ford says use 87 octane in the ranger and i trust engineers who built my truck. it's like idiots who ask "my oil cap says use 5W30, can i use 10W40?"
If your having Idle issues, higher octane isn't a solution. maybe a tune up is.
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Old 01-31-2010
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Quote:
Originally Posted by Machine090767 View Post
all i know is ford says use 87 octane in the ranger and i trust engineers who built my truck. it's like idiots who ask "my oil cap says use 5W30, can i use 10W40?"
If your having Idle issues, higher octane isn't a solution. maybe a tune up is.
Ha my truck say use 5W30, I ussually end up putting in 10W30. I can never remember when i buy it.

As for the tune up. My plugs and wires have right around 20k on them, I have run 3 cans of seafoam and a bottle of injector cleaner through my truck since july. I dont think I need a tune up.

The only think I can think of that would be a problem is that something in the fuel system is not working properly. I do not have a CEL. Although the higher octane fuel would not solve the problem if this is the problem.
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Old 02-01-2010
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Quote:
Originally Posted by malydeen View Post
Ha my truck say use 5W30, I ussually end up putting in 10W30. I can never remember when i buy it.

As for the tune up. My plugs and wires have right around 20k on them, I have run 3 cans of seafoam and a bottle of injector cleaner through my truck since july. I dont think I need a tune up.

The only think I can think of that would be a problem is that something in the fuel system is not working properly. I do not have a CEL. Although the higher octane fuel would not solve the problem if this is the problem.
If you must disagree with everyone else, possibly, just possibly, your injectors, fuel filter, or fuelpump is starting to go out...slowly but surely...Maybe the fuel isnt getting in to the engine fast as it should be, so with 87, it is really noticable since it burns quicker...the 91 burns better so the fuel system can lag a little bit without it being noticable....But its probably a timing issue or something like was suggested.
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