What could be causing my BAD mpg

[mcdaniel1991]

I'm averaging like 10mpg right now and it seems most people with the same upgrades as me are getting around 16-20
I know my front vaccume is messed up so the front driveshafts are locked in but other then that what else could I do hell is be happy with 15 I'm getting about 250 miles to a tank right now

 

[mcdaniel1991]

When I'm driving in flat ground about 70mph my Cts says my engine load is about 25%

 

[bboteler]

Fix the vaccum to start and check all the seals and bearing. When did you change filters last? What's your fuel pressure and egt's?

 

[Zmann]

never heard of the scenario of the Vac system taking a dump after someone locks in 4x4 but then can't unlock

I guess it's possible ??,, try switching to manual and drive a bit then go to auto drive a bit including reverse then reach in the knuckle and see if the ujoint can be spun by hand

matter of fact I might do that before you spend any time switching and driving just to verify you are correct about them being locked


I can give you the vac sequence in seconds and HG to unlock worst case just jack it up and use a hand held vac pump at the knuckle

 

[mcdaniel1991]

Yea it's locked I tried to turn the knuckle and it won't spin

 

[Zmann]

try what i posted if you want ?

I am sure you could pull the hub and manually unlock but not sure how to do that


let me now if the manual trick doesn't work and if you want the vac sequence to mimic the unlock signal

 

[mcdaniel1991]

I can't monitor fuel pressure or EGT right now I don't have the sensors. Fuel and oil filters were changed within the last 1k miles

 

[mcdaniel1991]

Yes I tried the driving around and what you posted if you can post the vac sequence ill try that

 

[Zmann]

here is what the inards look like

 

[Zmann]

found the manual override just go auto manual at the hub at least 2 times

Manual Override
The AUTO hublocks have a manual override selector dial, which, when turned to the LOCK position, will keep the hublocks locked (through the dial) at all
times, regardless of the position of the instrument panel MSS. (Always set both hublock dials to the same position.) If the hublock dials are manually turned
from the AUTO to the LOCK position, and the high vacuum level is applied to the hublocks (by switching the MSS from 2WD to 4x4 HIGH or 4x4 LOW),
the hublocks will be locked through the dial as well as through the internal spring mechanism. In this case, turning the hublock dials back to the AUTO
position will leave the hublocks in (spring) locked mode until the lower vacuum level is applied to the hublocks (by switching the MSS from 4x4 HIGH or
4x4 LOW to the 2WD). (This is not an issue if the hublock dials have been in the AUTO position and the MSS has been switched from 4x4 HIGH or 4x4
LOW to 2WD at least once.) Alternatively, the hublock mechanism can be reset to free mode at any time by turning the hublock dial from AUTO to LOCK
to AUTO at least 2 times.
Electronic Shift On-the-Fly (ESOF) Automatic Hublock

 

[Mason_lloyd]

try what i posted if you want ?

I am sure you could pull the hub and manually unlock but not sure how to do that


let me now if the manual trick doesn't work and if you want the vac sequence to mimic the unlock signal

I have had this same problem and still do I think. I haven't checked to see. But I've taken the tire off and messed with the hubs and unlocked them but for some reason it ends up being locked again. I know I do have have to change a u-joint in the front drive shaft but I don't think that will change it from being locked or not.

 

[Mason_lloyd]

And my hubs are Manuel lock.

 

[mcdaniel1991]

Thank you! That worked awesome!

 

[Zmann]

Good deal !

Mason I would try the same process

and also pull the hubs inspect clean old grease off with a solvent like wd-40 and re lube

worth a shot anyway

 

[mcdaniel1991]

need to revise this tread. Im still getting like 10-12 mpg daily driving to and from work, (5 MILES AVERAGE ABOUT 30MPH STOP AND GO). before anyone says it, i didnt by my truck for the milage but 11 mpg is not normal.

 

[duddy]

need to revise this tread. Im still getting like 10-12 mpg daily driving to and from work, (5 MILES AVERAGE ABOUT 30MPH STOP AND GO). before anyone says it, i didnt by my truck for the milage but 11 mpg is not normal.

For what its worth, I am getting 11 to 12 mpg in that situation with my 6.4. My weekend mpg is 16-19, but that is a lot of highway and 55 mph country roads.

 

[bboteler]

whats your setup? drw/srw, cclb, ccsb, rclb?? give us some info on the truck. do you know what gears you have?

 

[HeavyAssault]

need to revise this tread. Im still getting like 10-12 mpg daily driving to and from work, (5 MILES AVERAGE ABOUT 30MPH STOP AND GO). before anyone says it, i didnt by my truck for the milage but 11 mpg is not normal.

This is your problem. What happens to MPGs when you drive HWY speeds (55+) for more than 300 miles??

 

[mcdaniel1991]

I figured the distance and speed were hurting me. The truck is a ccsb not sure about gear ratio

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