Jeremy Kildow

Lary Ellis (Top)

The very best way to increase fuel economy is to shave about 5lbs off your right foot

BarryG

The 12 valve fuel pumps are pretty darn reliable and last a very long time and if it does fail at some point they are $100 and 30 minutes to replace. IMO you will be introducing way more potential problems with the fass and get zero benefit. Nothing against fass in a 24 valve they make sense. The pump in and of itself will not help mileage unless your current one is not good but you would probably know if it was bad just by driving it. You want good mileage be gentle on the go pedal, drive like grandma, don't drive too fast the wind drag vs horsepower is exponential in nature ie double the speed quadruple the horsepower. I found in my truck that weight in the bed did not do much to affect mileage but throw a trailer on even a light one it had more effect and if the trailer had a front on it all the worse, add sides even more so. Try checking out one of the hypermiling websites for tricks and tips.

oliver foster

I agree DON'T buy that FASS fuel system, I think they are garbage and will do nothing but introduce a host of new problems, leaks and an electric pump that die out of the blue.
Drop the F out of their name and you get what I call them.
They are okay on a 24V as you are already stuck with a crappy electric lift pump.
Stick with the factory style cam driven lift pump on your 12V, save the $400-$500... which will buy lots of diesel fuel.

To improve MPG, get a boost and pyro gauge.
Watch the boost gauge when you drive. The lower the boost #s you can keep to do the job at hand, the less fuel you will be using. Use that as a tool to adjust your driving style to get the best mileage.

cougar

I agree, stay away from an electric pump unless you are forced to. As for fuel mileage, my first question is what non-stock modifications do you have? Look at everything that you can reduce weight on and rolling friction.

patdaly

I am wit the others, for the love of god, do NOT complicate the thing. As for mileage, first make darned sure your fuel pressures are correct, 25-27 at Idle, and 32-35 at WOT for the P7100 trucks, it is easy to verify and one with a weak pump, overflow valve, or plugged fuel filter will drop your mileage quite significantly. Next is to make sure you are running in the efficient RPM of the engine, try and keep it between 1600 and 2000 RPMS at cruise, above that and mileage drops quickly.

As for the tank, no way on earth would I sump it, is your sending unit original with the steel lines coming out of the sender or is it the later replacement unit with the plastic pipes? If it has been replaced at some point in time, then there really isn't anything short of a fuel gauge sender failure that would make you drop the tank.

If you have the original steel lines coming out of the sender, and they are corroded and scaly, then this is a easy way to preserve your original sender and fix it so you will never have to deal with it again.
LarryB's Dodge Diesel Fuel Tank Draw Straw Sump Repair Kit, 1994-2004 - Dodge Fuel System Parts - Dodge Cummins Diesel LarryB's

Rare1

Jeremy, most of the after-market gadgets popular on this forum will decrease your mileage. Pick and choose carefully, see my sig below.
You didn't describe your truck or define your mileage goal. Remember that simpler is better, and stock is best unless you are very smart with your modifications.
The easiest fix is to eliminate smoke, which is unburned fuel. Don't get foolish with the smoke screw or boost elbow or fuel plate.
Keep in mind that some "good" features burn up gas, and can't be overcome. This includes big turbos, 4WD, fat tires, suspension lift, dually rear, 4:10 differential, injectors for HP.
Be sure your torque converter locks up properly. As Oliver said, get a boost gauge--this is the best readout of engine health. If you haul heavy loads, get a pyro gauge.

AlpineRAM

Hunting for mileage.. I know this, since diesel is always over 6US$/gal over here.

On a 12V- check your fuel supply so that it does not pull air- long hose on the water drain, back to the filler neck, open water drain while running, must not be cloudy.

Check injectors, pop pressure and spray pattern- these trucks have a history, be prepared to remedy wear on this.

Check timing- It may have slipped, maybe give it 1-2 degrees more than stock.
Get a clean air filter (can net up to 30% fuel mileage)
Check valve clearance- it has influence on mileage and longevity!
Without these basics it's hard to know where you are and what needs to be done.
All the comments about speed being an enemy to mileage are correct. Drive a truck like a sports car and it will drink like a tank.

SIXSLUG

All above then- fold your mirrors in, air up your tires to max, lower your truck, get moon discs for all four wheels, a lower air dam and a canopy, jettison all unnecessary items; all to reduce drag. Do not exceed 55 mph, limit your driving to flat or slightly downhill grades....

Seriously, though, all the guys gave great tips for your new truck to achieve its best mileage...it will only do so much and then you are at the point of diminishing returns for your efforts. Happy Thanksgiving!