Hey Ferm, or anyone that knows diesels

[oteps]

I would spin the rear and check the gearing. Maybe someone changed it. did u replace the down pipe when u did the exhaust? Its the one between the firewall and engine.
U may be better off buying a rusted out 4x4 truck with the gears ratio you want to use for parts. we have a lot of them up here.
I have a 99 f350 7.3. I was getting around 18 mpg. haven't checked it since stage 1 injectors and chip.

[spareparts]

yes, I replaced the down pipe. I did some checking and found an exausht leak at the turbo, I've got a turbo seal kit on order, once it gets here I'll take care of that and see how it does. Just drove it back from Raleigh, ran 68 most of teh way, averaged 13.7 mpg. I'm going to hook up a boost gauge before I reseal teh turbo to see what kind of improvemt it makes. The enbine seems to be running rich. The new pipe is already black and I get a strong diesel smell when its running(I checked for fuel leaks, none found). Low boost would caause this. Need a software to run on my laptop to check the tach. Anyone tried "torque" with a diesel? I had mixed results running it on my old phone

[THEFERMANATOR]

From what I've read the torque app can be hit or miss. As to the sooted pipe, that is pretty well par for the course for a 7.3L. That is a DIRTY friggen diesel engine, and will haze even when in good condition. An exhaust leak at the turbo won't hurt your milage, if anything it would help it by lowering boost. When you're not running loaded, the less boost you run, the better the milage(more boost than needed is just wasted HP). It's sounding like you have either bad injectors, or a failing HPOP. Those engines normally get pretty good milage even stock, and the common causes of poor milage is injectors, or low high pressure oil pressure not allowing the injectors to properly atomize the fuel. Valve cover gaskets can also cause all kinds of problems like low voltage to the injectors, and not allowing them to run correctly. Theres a reason guys that work on those engines make BIG money, they always need work.

[oteps]

My truck is 1600 rpm at 55 and 1900 at 65 if that helps. its auto with 3.55 or 3.73 gears and 265 tires.
If u end up doing injectors do not buy from full force diesel. I have a set and am not happy with them. They send me a bad injector and cost me a lot of money that was not paid back.
You can have a hydraulic shop make up a hose and gauge to check the high pressure oil side. You can also make up a gauge for fuel pressure, mine has ports for pre filter and post. Im guessing u have changed your fuel filter lately?

[smokeonthewater]

Sooty leaky issues at turbo almost always is leaky up pipes...
I can't remember if they make em for your OBS but if they do get the dorman bellowed up pipes....

Tuner... DP is the entry level.... PHP is WAY better.
I have Full Force Diesel injectors and when I was troubleshooting a possible injector issue they happily sent me a full new (loaner) set at no charge and even paid the shipping both ways..
Best customer service I've ever seen.

Your rpm's strike me as about right for 4.56 gears...
I'm running (33.5" tall) 255/85r16 load range E bfg mud terrains and love em

Intercooler, turbo, exhaust, air filter all help to lower egt's when towing heavy with more power but won't do chit for mpg's.....

The single best mpg increase I found was new brake calipers that didn't drag.

My crewcab dually 4x4 w 4.10's has neve done better than 15 and I average about 12-13.

My truck has bigger injectors, turbo, and tuning than yours being a 99.5 and then I've done several mild upgrades but I regularly tow 31,000 lbs w cruise set on 78 and rarely downshift even in the smokey mountains... Only one grade on I-65 that pulls me down below 65 mph with that weight, then I downshift to 5th and start gaining again.

A 4wd conversion will likely cost you 2-3 mpg btw

Oh and last tidbit... Pulling 31,000 lbs at that speed I average just under 7 mpg going back and fourth to Houston Tx from Louisville....

If I slowed down to 60 I'd probably get 11 mpg

[smokeonthewater]

OH and there aren't any "seals" in the turbo like you'd expect...

What they call seals are just little rings that help to stop oil from seeping along the shaft... They just sling oil inside the turbo...

If you have excessive play in your turbo rebuild it.. If not don't touch it..
If you have end play in the shaft replace it as it is done and not rebuildable.

There IS an oring seal in the compressor side that afaik never fails but even if it did it would be clean boost air and not sooty exhaust.