ok...heres the deal. I own a 2005 f150 reg cab w/ 4.6. My gas mileage is killing me. I can only go around 170 miles before my low fuel light comes on. I figured out the mileage last night and it comes out to about 8.9 mpg! It makes me sick. I absolutely love my truck, but this mileage is eating me alive!The truck has custom exhaust which is supposedly supposed to improve mileage... It also has 3:73 gears and is tuned with a diablosport predator. Im not sure if this would effect the mileage that much but the truck does have 33" nitto mud grapplers w/ 20" wheels..i know this cant help but would it really effect it that much? This week its also been about a steady 25 degrees throughout the week. Is there anything I can do?

 

those 20 inch wheel and tire combo doesnt help lol. 8 miles a gallon doesnt sound right. how about your tune up stuff?? plugs,wires, fuel filter etc...?? a bad 02 senser can cause bad mileage also. are you getting any check engine lights??

 

Ouch, something is wrong. I have the scab, 4.6, auto, 4x4 with 3.55 stock and im getting 330 miles before the low fuel light comes on. 26 gallon tank if memory serves, usually fill up with about 22 gals. So im getting about 15 and I am pretty hard on this thing.

 

Have you adjusted your miles you drive? Since you've added bigger tires, the computer won't count off the miles as fast. You need to find out what the factory tire size was, and then calculate the difference. Or you can set your truck at 60mph on the interstate and then watch the mile markers and see how far you are off. You may only be ticking off 8 tenths for every mile. Hope this helps.

-Funkster-

 

hes right, those bigger tires are spinning at a different rate now. the odometer and speedomer are probably off. it still thinks you have the stock 16 inch wheels.

 

8.9 MPG is not good at all. I have an 06 SUPERCAB with a 4.6 Liter in it and I get anywhere between 16.5 and just shy of 20 MPG. I drive highway miles and I don't really look at my city miles. Your bigger tires and wheel are not helping. But one thing over looked here is! Have you taken into account your "GEARS"??? I know in my old Mustang I had with gears in it, I had to convert my speedo/odometer to the new gears. Is that an option in your Diablo tuner? If it is you may want to look in to that. If not? Tune up. Or take it to a dealer and get a diagnosis. Probably cost you between $80-120. But if you save money in gas. Hey!! It's worth it.
Natty...

 

Ok, you make it sound like you are basing your MPG off of when the light comes on as an indicator of having no gas left. You do realize you have several gallons still at that point, right?

To properly calculate it you need to A.) Figure the difference from your wheels/tires, and B.) Figure out how far you go and then how many gallons of fuel you can pump the next time you fuel up. Don't use the light...

 

Also take into account winter gas blends, and how long do you let it "warm up" before you drive.

 

http://www.miata.net/garage/tirecalc.html

Figure out your rev's per mile and tune it accordingly with the predator, just did this and gained some mileage back.
BTW the option for tire revs per mile on my predator was under axle ratio and my stock revs per mile were like 720 with 16's. Do the gears too.

 

Well, I bought the truck a month ago with 11,500 miles and the seller had the stock wheels on it. A few weeks later I bought the 20" wheels with 33" mud grapplers...he told me that the truck is tuned and should be fine....however he didnt give me the tuner...and won't return any of my phone calls in reference to selling me the tuner...I heard that the tuner saves the original stock computer settings the first time you plug it in....if so would I need the tuner that was used on my truck or can I just buy another tuner and some how reset the truck to stock? I need to buy a tuner anyways because I will be switching the wheel/tire combo during the winter and want to be able to adjust the speedo. I never check the gas mileage before I put the new wheels on it so I dont know how it was before..but something is def not right..I had a 98 f150 w/ 4.6 a few years ago and it got around 10-11 mpg city which sucked, but id take that over 8! Thanks for your help guys.

 

It's a shame you don't get the tuner.
If there is ever a problem and the dealer reflashed the PCM, you lost the tune.
If emission inspection finds a fault that might be tuner related, then what?
Are you going to dinner anytime soon and having soup without a spoon.
Good luck.

 

Yeah, people REALLY don't understand the procedure, risks, and possible repurcussions of "tuning" their truck. Just read the chips and tuner's section of this site, and you'll se tons of questions like this. I just feel sorry for people that break their truck. AT LEAST THE DEALER CAN FIX IT!

 

is there any way to get my truck back to stock without the original tuner? It would be great to just get it to stock again and bite the bullet and by a new tuner so i can recalibrate the speedo for the tires...is that at all a possibility? I heard you can disconnect the battery for 15 min or something? Id rally appreciate any feedback

 

You have to go to the dealer... disconnecting battery will clear codes but not erase the program. It's stored in non-volatile memory (like a USB thumb drive) and doesnt rely on power to maintain the tune.

 

If you plan to get the tuner then its a waste to pay the dealer to put the stock tune back in, cause the stock tune isn't tuned for the tires either. Only if the dealer can tune for the tire size then i would do that.