What will happen to my MPG if I switch from 87 octane to 91 octane?

 

Simply by using 91 (93 in my case) shouldn't give much of a boost in fuel economy without the aid of a chip. I was averaging 12.5-13 MPG's with my truck using the 87 octane program for my Superchips tuner. I switched to the 93 performance mode and jumped to 14.25-14.5 MPG's! I'm hoping it gets better now that I just put on my Spintech exhaust, which I absolutely LOVE!

 

the truck from the factory is set to perform best with 87 octane and so yeh u get small difference purely throttle responce but thats about it by goin with 91 octane so just save your money

 

Simply switching octane won't help MPG in many cases.

Not to mention, even if you do gain some MPG, the extra cost of the higher octance gas will probably not put you above anyway...

 

Depends on what the engine was designed to use. My 97 4.6L was designed around 89 octane, and it runs best on that. I haven't noticed any increase in gas mileage going up to 91 octane. But, the higher octane does give more power when going over mountain ranges such as the Rockies. I get knocks under load and slow acceleration when using 87.

My wife's new 6 cyl Liberty is made for 87 octane and runs like crap on anything over 89.

 

Thanks for the info. I am getting some pinging during WOT but it may be that the 87 octane I am buying is not really 87 or maybe my 5.4L engine needs a diagnostic run on it. It has about 46,000 miles on it now. God only knows what kind of knocking will occur if the temperatures get into the 90+ range instead of the 70's.

 

thats just sparknock from cheap gas is all i wouldnt worry about it just buy gas from a better place or buy like 89 octane or somethin. all that noise is it the piston knocking the side because of a slow burn on the fuel and its not burning evenly. but dont worry about it unless u think its a major issue like if its doin it real bad maybee an spark plug is fowling up or an injector is quitin out on ya. but "spark nock" is common

 

Try cleaning your MAF sensor.

Regards

Jean Marc Chartier

 

Jean,

I poured a few drops of acetone over the two MAF elements and then blew it out with an air hose. The back element (right) looks darker than the front element (left). The cleaning did not change the color of the back element. Should I remove it and try to clean it with a Q-Tip? The picture also seems to show some brownish crud behind the back element but I did not look at it when I had the MAF out.

 

be careful when cleaning those if u bent or get any residue on one of the elements in there u can throw the calibration all off so be careful when cleaning it. but it looks clean to me.

 

Oops, I did bend one a little when I tried to clean it with a Q-tip. I guess I should disconnect the battery and make sure the engine still runs ok instead of letting it slowly migrate to a non-running condition as I drive 300 miles once a week.

How much does a replacement cost?

 

Well, I disconnected the battery to reset the computer. The truck is running just fine. I got a part estimate of about $153 from Ford for the MAF. I will probably be able to check my MPG this week to see if the slightly bent wires affect my MPG any. I don't know if the bent wires would make the engine run lean or rich.