I have a 2008 crew cab reg box with 5.4l with some mods like k&n cai, magnaflow exhaust, throtle body spacer and bully dog gt. I thought that all these put together would help fuel mileage but it never changed a thing. Also does anyone know if this year of motor has the spark plugs siezed in the block with that 2 piece spark plug.

 

rarely if ever will adding performance parts give any real world MPG increase...

your plugs will be the newer 1-peice design so no worries there...

 

I have an '09 truck, and there are times when 10mpg is as good as it gets. If I'm going against a strong headwind, my fuel efficiency stinks. But when the wind isn't blowing 25mph against my grill, my big truck will pull some respectable numbers for what it is.

Mods don't typically help has engines gain much fuel efficiency. I'm tuned with a SCT X3 and have not noticed any boost in MPGs.

How's your truck set up?
Tire size?
Axle ratio?

Unfortunately, 3.73 and the 5.4L don't get the mileage boost many think over the 4.10 and 5.4L combo. Especially with larger than stock tires.

 

My '08 4x4, X-cab, 5.4L auto has the K&N CAI, aftermarket SIDO muffler and Superchips Mileage XP tune installed, 275-70-18 tires, 3.73 rear end. I'm pulling down 16.8 mpg at 60 mph (I got 17.3 driving from Houston to Lake Jackson but the terrain is flat), 14.8 at 70 mph. I'd chuck the throttle body spacer; with modern fuel injection, rather than throttle body injection, some believe they only rob performance/mileage.

I had the troubled plugs in the truck when I changed them (93k miles on them); Denlors Tools has the extractor tool for about $90 shipped to your house (if one or more breaks, get the tool).

Some aftermarket parts help with mpg - as well as performance. You won't get both.

 

a double length cab and an 8' bed is the longest (and heaviest) combination you can get in a F250.

Combine that with the smallest numerical gear ratio and the smallest engine available and you've got a setup that has to work pretty hard to get moving and keep speed up a hill.

One thing to do is to make sure you're running the recommended 65-psi front and 70-psi rear tire inflation pressures... it will lower rolling resistance.

 

thx rebel will check my tires

 

for tires i got 275/70/18 and i'm not sure the gear ratio. Is there somewhere on the truck that would tell me that. And maybe ill take that trottle boby spacer out and see if there is a difference.

 

I forgot to say that i do have about 600 pounds in the box for added traction in the winter.

 

Look at the door sticker, tell us what the axle code is. That will also have the recommended tire pressures.

 

I have the 2008 cc lb 2wd 373's and have a high camper top with the tool bins and also carry a spare 98 gal. fuel tank. The truck weighs 9500 lbs. with the basic tool and parts load and full fuel tanks and in the city I get 10.4 mpg's, or 10.8 mpgs when the air is cold in the winter time. That is with the stock 275x65x17 inch tires at 80 psi. I just swapped to 18 inch wheels with the continentals with no difference. I don't do too much highway driving but when I do I probably get maybe 2 more mpg's. I would bring your truck into the dealer and have them re-flash the computer you never know maybe it will help. I have a heavy foot sometimes, but I really don't think it makes too much difference either way. Did you try hand calculating the mileage or do you go by the lie-ometer?

 

Part of your mileage problem may be contributed to your tires; as you are looking at the door post for the tire pressure, note what tire size is on the sticker. You'll probably find your current tire is much taller than the stock tire (registers fewer miles and actual speed is higher than indicated) and that is causing your computed mileage to be worse than it really is. I took my truck to the Ford house and they calibrated the speedometer to the tires I have installed. But the calibration is only worth less than 1 mpg; the 600 lbs in the bed isn't helping mileage too much, either, although ballast for traction can be priceless.

To get an idea of what the error is, use this link: http://www.miata.net/garage/tirecalc.html For the "stock" tire size, use the size on the door post sticker; use the current tire size as the "new" tire.

 

I used my bully dog screen, it gives me instant mpg, maybe I should take a drive from right full of gas then go back and top it up and calculate from there.

 

Try to keep the rpm's below 2500 when you excellerat. Fill the tires to the max on the tire not the door.
I lost 2 mpg's since nov. due to cold weather and winter gas.Got most of it back with driving habits and filling tires.

 

I have a 08 CC short bed 2wd and in the last month with the cold start warmups the lie o meter says around 11 mpg. Hand calculated its 10.5 to 10.7. Just did a mostly highway/interstate drive of 200 miles plus and LOM said 14.7 hand calc. was 14.5. The lie o meter is constantly .5 to .2 higher than actual numbers. Also, my truck had the two piece plug, broke one removing. Someone here had a build date that after that date 08's had the new style plug. Don't remember the date, but at the time I checked and mine was manufactured about a month to soon. Good luck.

 

The dealer told me my '08 still has those plugs.