in the last couple of weeks my mpg has dropped almost by half i used to get almost 200 miles per tank now im getting just over a hundred the hubs are not locked and the truck is running fine like it did before this started to happen i need to replace my battery cables but that shouldnt do anything with my mpg i have a pensicola referb ip in it i got it in september i do not know how the injectors are can anyone help me figure out wat is wrong?

 

Is someone syphoning fuel from you.....
Check your air filter.......squirrels and mice love to make nests.
Any excess smoke......
Where are you getting your fuel........@ a reputable source?

 

air pressure is major loss as well iv noticed,at least with 6 wheels.
cold brings down tire pressure.check them often and keep 'em at max psi.
winter blend fuel has less BTU's,so your gunna take a hit no matter what.but all the more reason to keep track of things better.
long periods of idle time = killer.
do you have a block heater? use that.or if you dont want want the electric bill to go up,just start the engine.insure good oil pressure.wait about 2-3 minutes and just get going down the road.she'll warm up much faster that way for ya and count as miles on the odo rather than 0 sitting still.
37" mudders = a lot of rolling resistance in general,let alone pushing through 1/2" snowy/slushy roads too.compared to stock 235's,those are likely a good 1.5-2mpg loss right there,rough guess.

 

i just put a new spectre filter on and i do not hve the tires on yet i have 265 on right now the fuel i get is from shell and thats all i use it has only hapened in the last couple of weeks and right now its not that cold ill check the tire pressure i havent for awhile im just really confused and i know the milage is atleast somewat right because iv only drove to school this last week

 

could injectors going bad be a culprit to?

 

indeed.
however there are large and small combined variables than can effect fuel economy greatly.
the first thing you need to do when tracking fuel economy is know how to do it correctly,and make sure its accurate.
first and foremost; correct odo readings.if this isn't accurate,it's over before it starts.
OR don't go by the odo if you know it's off.use google maps or gps for example to track miles driven.
with dual tanks,its VERY important to make sure the FSV(fuel selector valve.located on the frame rail) it......uh oh.do i dare use this term here lol......electronically switches open and closed the front or rear tank to draw from.a "fairly" common failure of these,is they will may draw from the tank selected,BUT return to the opposite tank! as you could image,this would make fuel economy look disastrous!(use the search function for more details as i could write a book or at least whole thread devoted to just this.....oh wait...i did lol.you'll find it.)
correct way to track fuel economy;
a.forget about short trips,and or spikes of 20 mpgs(if your lucky to get them lol)
b.fill the tank.select reset on the ODO (or write down the current miles)
c.run until your is 1/8 tank or so (no don't be silly and try to run it close to dry! thats the fools way.and i'll explain why.)
d.fill the tank again.take note of how many gallons it took,and record the miles driven.divide and record.
e.repeat as much as possible,and here's the most important part;as consecutive as you can.this will eliminate the fill up errors between fill ups.
f.now take for example 10 consecutive fill up's back to back,and you now have a VERY dang near perfect average mpg reading.
g.continue if possible,so you can tell when something goes askew,you can adjust asap,saving $ before you spend it needlessly.


once fuel economy is tracked correctly,
on an older diesel engine,this would be my priority;
1.ensure the truck,rather than the engine is "economy clean".what do i mean? by examining the brakes,to insure the tires roll freely.
axles must be flushed every 100k.how longs it been? perhaps consider full synthetic since its only a small amount of juice,and a long duration period between flushes right?
2.engine.
a.compression test.pass or fail? fail= hard starts and poor power and economy.rings or valves or time for a rebuild.
if she passes i own it; she gets a total diesel tune up if its been 100k plus since.
ip
injectors
timing set
air filter (and checked every 5k miles by the way)
CDR replaced (screw cleaning.that's every other oil change.every 100k she's had enough.diesel and oil cost WAY to much to frig around with today.)
fuel filter.
oil change.have you considered synthetic yet? how about at least spending an hour or two researching it with an opened mind? and no,i don't mean just here to get opinions,but sites that provide facts with studies and charts.
ok.i guess i'll stop there for now,and see how ya do lol.
good luck!

i should add,its not just about the truck either.it's about the driver as well.
have a look here:
http://fueleconomy.gov/feg/driveHabits.shtml

 

my family has a log book in every vehicle and we keep track of the milage and everyhting every fuel up and i dont use my front tank unless a absolutly have to which has been once since i bought the truck, i had been getting 200 miles per tank till recently i dropped to 100-120 driving the same way. from my last fill up i only drove to school for a week (5days) which is 5 miles away and im at half a tank already

 

I just going to add my two cents in here, take it how you want.

First how has the truck been starting? the mechanical fuel pumps on these trucks are prone to leaking and do cause starting issues. They can be replaced with electric. A chevy big block mechanical fuel pump block off plate fits perfectly, and a Holly Red fuel pump will supply more than enough for the motor.

Second your injector return lines. the ones on my old 7.3 IDI cracked and leaked fuel on to the intake plenum. I cold only see the odd tiny wet spot under my truck. but once you started driving it they poured out the fuel.

Those are two quick common places to look and a good start before you start getting into hours of work

 

One of the first places I would look, has the engine been making oil?

Not uncommon for a failing lift pump to put fuel into the oil.

So if it was using some oil, and that has suddenly reduced, fuel may be making up the difference.
It it was not using oil, and now you are over full, you may notice oil leaks have increased but the oil level is not changing much.

It don't take much time sitting idling, burning fuel while no miles are going on the odometer to drop MPG rather hard.

 

Don't happen to have a frozen emergency brake cable do you? In cold weather moisture can freeze in there and leave you with dragging brakes... just a thought since the drop came on suddenly...

 

Warm the engine, drive 5 miles.
Warm the engine, drive 5 miles.

You are probably spending almost as much time on warmup as you are driving.