Hello good people!

I own a beeeautiful red 1997 F150 supercab, 4.6L, auto. about 130.000 miles, in sunny California. Have been using highest grade gas since I bought the truck.

Recently did a full tune up, spark plugs, wires, clean injectors, etc. and mileage improved from about 11 - 13mpg (city - freeway) to 13 - 15 (which I still think is not too good...)

Because of gas prices, I decided to do some testing with lower octane gasoline, since I learned that the higher the octane, actually the fuel resists burning, to prevent pre ignition on high compression engines.

I filled the tank with 87 and drove till empty with no difference in MPG (did notice some pinging going up a hill), after that I filled up with 92 and again no change in MPG.

Because of the pinging I noticed with the 87 fuel, I decided to try 89 octane. Well... MPG went waaaay down to like 10 - 12!! I thought there might something wrong, although there was no difference in the way the engine was running, always smooth as silk.

Filled back up again with 87, and MPG went back to "normal" 13 - 15.
Same gas station, same driving habits, same trips, etc.
Any sensible explanation?
Anybody?

 

The truck is setup to run normal on 87 gas...You mess up your computer system some with using different fuels...Try getting a K&N filter...that has helped my truck work better...You may need run a good cleaner through your rig as well...

But I'm sure their are guys here that can explan this better than I can..but you do what your think is best...I just got 17.64 MPG on some mixed city/highway driving with the truck not carrying anything...I have the 4.6 motor and reg.gas or 87...We have use a bigger gal than you do as well...4.5 liters = 1 gal in Canada...

 

K&N already in when I bought the truck last october, what do you mean by "run a good cleaner"?

 

you should use only 87 octane. Your PCM has no idea what gas is in the tank and it is programmed for 87. 13-15 MPG is normal

if it is pinging you prolly need to clean the EGR ports which is very very common on a 4.6 (do a search here) and some think (including me) that running 92 clogs the ports faster.

change your fuel filter before running a good injector cleaner. Use BG-44k or Techron and make lots of short trips where you turn the engine off so the cleaner will sit on the backs of the intake valves.

welcome and later-

 

take a look at the sea foam post on here,i saw it and decided to try it.that stuff works pretty good,better than anything else i've tried

 

The lowest octane you can run without pinging.

Higher octane fuels burn slower, making for less power and poorer performance. The adaptive strategy for your truck tried it's best to compensate for running a higher octane fuel. My advice would be to run 87, disconnect the battery to clear the fuel trims and drive it around town and on the highway for it to re-learn.

As someone else mentioned, with 130K miles, you may have a clogged EGR port that needs cleaning.

 

How about we discuss and learn about "Octane". When we "crack" crude, we are breaking it up into its different lenght hydrocarbon chains. One hydrocarbon atom is known as Methane. Three atom length chain is called propane, starting to sound familiar? Butane has four, pentane has five, hexane has six. Now comes the chain lengths that are used in todays gasoline. Heptane has seven and OCTANE has eight. Heptane becomes unstable when it is compressed and that property is used to ignite the OCTANE in the combustion chamber. In basics, when you are buying an 87 OCTANE gas, you purchased a fuel that is 87% OCTANE and 13% heptane. Premium gasoline that is 93 OCTANE is basically 93% OCTANE and 7% heptane therefore, the premium is harder to ignite. When you use a premium gas in an engine designed for 87 OCTANE fuel, you are effectually retarding the timing in your engine. Because of the lack of heptane, the flame front is slow to start and doesn't develope as it should thereby increasing the amounts of emmissions that your engine has to deal with. In extensive lab tests, no engine will run stronger or get better fuel mileage on a fuel of higher OCTANE rating. While some folks "feel" that their engine runs stronger on a higher octane gas, this does not hold true on the track. If your engine is suppose to use a gas of 87 octane, that is the BEST rating fuel for it.

Please remember that this is in basics, there are considerably more details that go into the formulation of todays gas. Hope I didn't confuse any of you.

 

Well I was right...this group can build you a better truck if they want to...I should also say that your tire type and air pressure will help or hurt your gas mileage...Keep 35 PSI in my tires and only check them when they are cold...I use only 5w20 ford oil as well....The motor needs this type oil as the engines are made so tight now...Saved wear and gas mileage too...Hope you feel you got some good tips...

 

Are you kidding?? Absolutely amazing!! Itis is impressive the amount of knowledge that can be obtained from a forum such as this and all the good people willing to share their time and minds.

It is also amazing how many people (like I did myself), hold the misconception that running a higher grade fuel would be better for their vehicles...well, you get what you pay for, right? Right...

It wasn't until recently since I learned a little about fuel grades from a dirt bike forum I'm a member of, that it donned on me how much money I've been wasting unecessarilly!!!

Labnerd, no, you didn't confuse me (much...), and thanks for furthering our knowledge.

for you all! (with moderation, of course...)

 

Thanks, I learned something! I hear gas is good for about 30 days so I use Sta-bil fuel stabilizer when I have gas around the house for several months or when I put the mowers and stuff away for the winter. What does the Sta-bil do?

http://www.goldeagle.com/sta-bil/all_about_sta-bil.htm

 

Yeah, I am going to agree with soudorio. This forum is incredible. The members in here have helped me with a bunch of things I otherwise did not know about. Very appreciated. Keep up the good work.