Well, after reading a couple of posts about the difference between low octane and high octane, I went from the high octane (92) to the low stuff (89). Now, I have the Bosch Platinum +4 spark plugs in since Dec. 1st, 1999 and have been running the high stuff with mileage around 15.5 mpgs (highway). I changed the octane and drove home, where the 15.5 usually is at and noticed I was burning way more fuel than usual (by gas guage). The truck has no mods, except the plug change and has about 121,000 kms on it. Anybody have the same type of situation, would love to have the old mpgs but not for the price of gas now a days. Any ideas or thoughts would be greatly appreciated.

Have Fun & Keep on Truckin'
Dean

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1994 F-150 XLT Supercab, Long Box, 302 EFI, Automatic, Royal Blue in and out, Captain Chairs. Chrome Rims 15x8's, Michelin LTX M/S 105S 235/75R15 (Summer), OEM Aluminum Rims 15x8's, Michelin LTX M/S 108S (Winter), Lightly Tinted, Soft Tonneau Cover, Ford Receiver Hitch Cover & Lock, Alpine CDM-7829 Head Unit, PPI 4800 Amplifier, Kicker 10" Solo Baric Sub with Custom Box and Kicker Impulse 6.5 Mid & Tweets.

 

I used to run 89 octane in my 89 302 with a 4 degree advance. Got about 14mpg's avg, and then I switched to 87 and reset my timing to 10. I did a check and got about the same, 14mpg's. But the truck's responce is slower, not considerably, but slower.

 

Getting 18 to 19 mpg on 87 octane fuel on strickly Highway driving . 1998 f-150 4.6L. Surprised by these figures to say the least.

 

I think the new engines adjust the timing automatically based on knock and O2 sensors, but it would probably take more than a tank to adjust. The manual says at least 87, so I put 87 in, the compression ratio doesn't require the higher octane. Mileage also drops w/ oxygenated gas. In any case, it takes a couple of tankfulls of the same type of gas to get accurate mileage readings IMHO.

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'99 Lariat Supercab 4x4 SS
5.4L, 3.73 Diff (9.75" LSD Rear, 8.8" Front)
ORP: Skid Plates, LT265/70R17 GY Wrang. AT/S
Group III towing: HD Electrical/Cooling, GVWR 6500# (Extra leaf spring).
Step Bars
4W Disc anti-lock brakes
K&N filter
Stock Items That Differ Across F150s: Steel Driveshaft, Oil filter bolted to engine w/ drip guard, 4R70W transmission.

 

Every article I have ever seen in print or on the tube says that it is a myth that increasing octane above the minimum requirements leads to increased MPG. I would love to see a long term study on the fact using two indentical trucks with the same driver going on the same trips.

Personally, 92 octane is between 12 and 16 cents per gallon higher here than 87. That can add up big time. I would have to get a huge increase in mileage I think to make that cost-effective.