Hey guys, this problem is on my 93 F350 7.3 N/A. Ive been getting poor (14-15mpg) fuel economy since last fall, but i attributed that to winter blend fuel. But now this last fill up ive only put on 64 miles, and ive used over 1/2 a tank of fuel!!! There are no leaks on the ground, the oil level has not risen, its not bypassing to the other tank, and its not smoking excessively. WTF?!?!? Anybody have any ideas where i could look next? At this rate im gonna have to start driving my 89 every day, cuz the 7mpg it gets is better than this!!!

 

your timing might of moved, mine will do that sometimes, I'd get it checked and change the fuel fitter.

 

someone could have siphoned your fuel

 

I doubt anyone siphoned the fuel, I know its not impossible, but ive never had that problem before. I can check the timing, why do you say change the filter?

 

a Half plugged filter can cause a number of diesel problem, if you haven't done it in a while you should change it.

 

but cutting my mpg in half?

 

Does the truck feel like it's down on power?

 

Your ip needs 6psi of inlet pressure to run properly, If you are getting less that 4 it messes with the pump, Also have you been bragging to any of your friends about mpg? or did the kid next door get a diesel?

 

No to both your questions, why do you even ask? I track my mileage so i know if and when things change, signaling a problem

 

Fuel selector valve pulling from one tank and returning to the other?

 

That's actually a good thought; apparently, they usually stick returning to the /rear/ tank, so if you're monitoring your /front/ tank, you might want to check how much you've got in your rear.

 

Your friends must not be jokers like mine, suck five gallons out this week, put it back next week just to mess with you

 

Have you checked you lift pump? When mine went out it didn't start transferring into the block, but started leaking out some sort of vent port on the top of the pump. I didn't notice an drop in performance but mileage did go down a bit.

I personally wouldn't suspect the engine tune up, if mileage dropped off that much that quickly there should be a noticeable drop in performance.

 

This is perhaps too obvious but I have to ask... Did you verify that the tank was half empty by filling it or is it just what the gauge says? (i.e. sending unit/gauge problem?)

 

lol no my friends dont do stuff like that... its too much work lol.

I am just going by what the gauge says, i know its not anywhere near accurate, but it does still work. Consider my mpg numbers a ballpark at this point.

And no to transfering fuel to the other tank, that was the first thing i checked.

Tonite i checked my air filter, much dirtier than i thought it would be. Also all sorts of oily in the intake. Removed the CDR, and am currently soaking it in parts solvent.

Just for chits and giggles i fired it up w/ no air cleaner or cdr, and even just sitting in the shop i can tell its breathing alot better. But now it also smokes grey constantly, and gets very heavy w/ throttle application... now im getting worried