newbie with a fuel issue.

[dennisg313]

Hey fellas newbie to the forum and new to the diesel world. I have a 06 f250 6.0 100,000 miles only mods that i have done is the exhaust from turbo back 41/2 lift and 35s on it
I have had it a year now and im only getting 8 -9 mpg. What in the world is going o.? I have just installed a new ficm as i had a ficm code p0611. Drives great great throttle response but with or without a trailer i get 8-9 mpg. There may be an injector sticking open would that cause such mileage with no black smoke or fuel in the oil? And I've also notices the front hubs may be bad. The axle spins when its in 2wd and clicks when i turn 4x4 on like a baseball card in a bike spoke. Any help is appreciated.

[TKOPerformance]

The lift and taller tires isn't the hot ticket for fuel mileage. Yes, the effective gear ratio has been reduced, as well as highway RPM, but the added rolling resistance and rotational weight is sucking up fuel. Being higher up is also increasing your air resistance.

That being said I can't see a drop down to 8-9mpg. That's super piggish even by 6.0 standards. I get like 12-14 city and 14-16 highway with all the mods in my sig and a pretty heavy right foot.

If you were overfueling you'd be getting a lot of black smoke, so I don't think that's your problem. Yes, some would likely end up in the oil, but it would burn off too, causing heavy black smoke.

One possibility that you are not going to like is a cracked injector cup or bore. This could be leading to fuel in the coolant and no black smoke. I'd check the degas bottle and see if you have any grayish junk in there. If so then pray its just a cup, as those can be replaced. If the bore's cracked it's new head time.

You will see mileage diminish with wasted front hubs, but I don't know about that much. You can test them pretty easy, just pull off the brakes and give them a spin. If you are getting grinding noises, a lot of resistance, or slop then the hubs are junk. You are not going to like what they cost either. At jobber I think I paid over $300 a piece for mine.

That clicking sound could easily be a bad bearing somewhere. What do you mean the axle spins in 2WD? How'd you discover this?

[dennisg313]

My boss was riding behind! And noticed the front axle like the u joints were rotating i thought that was normal. And before i did the ficm swap we went through each injector and shut them off one by one
And noticed injector 6 when shut off made no noticeable change in the idle like the other 7 did.

[TKOPerformance]

The front driveshaft spinning in 2WD is normal. If you could hold it still it would stop. Basically you are getting fluid "roping" inside the transfer case, which causes the shaft to spin, but there's no power behind it because it is only coupled by the fluid.

Well, a 7 cylinder engine is going to be less efficient for sure, because one cylinder is just along for the ride. Its a parasite, taking power from friction, but supplying nothing in return. That said, 100k is a little early for there to be injector issues if proper maintenance has been followed. You might try running a fuel system cleaner through it, like a full bottle of CRC Diesel Kleen. I had some problems when cold, etc. and though my injectors were starting to go, but one full tank of fuel with a bottle of that in it and everything was back to normal. It's well worth a try. Another thing you might consider is a switch to synthetic 5W40 oil, like Rotella T6. With the oil firing system these trucks really like the synthetic.

[dennisg313]

I can say whwn i changed the fuel filters the one on the frame rail was black i bought the truck a year ago had 86000

[TKOPerformance]

Improperly maintained fuel filters will kill the rearmost injectors first. Fuel supply to them is worst because the fuel has to flow past the front injectors first, so if fuel is diminished from a plugged filter it will likely kill #7 or #8 first.

I have heard several stories of guys buying trucks with lots of miles on which the frame mounted fuel filter has never been changed. Really, really not good. Both filters should be changed every 12.5k max. What did the filter in the housing on top of the engine look like?

[dennisg313]

The top filter looked okay. The injector that was having an issue was #6 and my clicking noise we looked today and noticed somehow the right hub wasn't completely unlocked. And was extremely hard to turn from lock to unlock

[HeavyAssault]

How wide are those 35's?? Sounds like maybe the front hubs are stuck spinning the axles, this causes drag. It shouldn't be dropping you to 8-9MPG so expect another issue is lurking there somewhere.

[dennisg313]

There 12" or 12.5" wide and i get the same mileage with the stock tires and wheels

[HeavyAssault]

There's something not right. You should be getting better MPGs. I say this as I run a 6" lift and 35's getting 14-16 city on the regular.

[dennisg313]

I got ahold of a snap on solus scanner and i got my cousin that knows how to use it were gonna see if we can find anything unusual and chrck the injectors

[dennisg313]

So we ran a scanner on it, nothing out of the ordinary torque convertor locked up like it should all injectors are closing and opening properly, everything looked fine. ***. The only thing i was thinking is if the previous owner had the pcm flashed for towing whatever 5th wheel trailer he had. Any other suggestions the wheel bearings turned fine no slop, the hubs looked good. Whats next??

[HeavyAssault]

Power Hungry Performance for PCM and FICM roll back tuning.

[TKOPerformance]

Any tune should actually increase mileage. I saw a solid 2MPG from a hot street tune, even driving it pretty hard. With more power available I'm just on the throttle a lot less.

The hubs are often hard to turn, especially if they aren't used that much. I saw no real reduction in mileage driving around with mine locked, so that I could just pop it in and out of 4WD with the t-case lever during bad weather. Maybe highway mileage would show more of a difference, but around town and mixed driving it was pretty much the same as always.

I'm going to ditto the rollback tuning.

[Ford06]

Also do the blue spring fuel pressure regulator upgrade if it hasn't already been done. It may not help your mileage, but is cheap and will help your injectors last.