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Thats a big question.

Maybe install a new air filter.
Make sure your tire pressure is high.
Check for vacuum leaks.
Drive real light on the throttle pedal.
Try to drive with a big tailwind.
 

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Sell it, and buy a motorcycle.
 

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OK, I realize this is an 8 year old thread.....but....I ordered our van new w/ 3.55.
The only time I got 21 mpg was driving all day through Ohio on I-75, construction zones, 45mph.
 

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Like @anash13 said,

The 3.55 LS rear end helps, and anything under 1850 RPM will get you good MPG. When I set the cruise to save fuel I use the RPM on the Scangauge II or AIC and use the RPM's to set the speed. When you go over 1886 RPM it starts using alot of fuel.

The old black CPS cam position sensor helps alot too, the new ones are faulty.

I think the magic number to save the best fuel is 57 MPH or so. I know it's slow but the RPM's are about 1820 or so.

I will check the next time I try it. My van idols at 664 RPM when warmed up with the old 2001 black cps.

Running T6 oil 16 quarts with the 3 quart oil filter, Amsoil synth in the trans with the Sonax valve and trim springs,
and Amsoil full synth in the 3.55 LS rear end and the magic Centramatic wheel balancers that balance the wheels 100% without any wheel weights. Even if you have a warped rotor or bad tire it will still balance the system. The balancers make the van track perfect, no drifting or bump steer and the tire tread wears even across the tread.
Alcoa rims hand torque to 140 ft. lbs. If your rims are not torqued to spec, you will be unbalanced and waste fuel.
The Alcoa 167041 Classic are rated at 3750 lbs. max load, highest rating in it's class. I see so many people installing fancy wheels with very low weight ratings, and they tow with them with incorrect backspace and offsets.

If any of you fine people tow get a set of Centramatic wheel balancers for your trailer too, it will be 100% balanced and make you save fuel at the same time. They are a must. They cost about 200.00 a set of four in Aluminum. Aluminum rims get the aluminum wheel balancers and the steel rims get the steel balancers. Call the comp0any and tell them your vehicle type, rim type and size etc. The balancers start working after 23 MPH with the gyro effect.
You can paint them also. I just leave my balancers natural Aluminum. 18 years old and still working like new.

My van has two fuel tanks, 35 main and 27 Aux, 65 topped off. It's about 485 lbs. of fuel topped off and it makes my van just over 10,000 lbs.

80 lbs. rear and 65 lbs. front 245/75/16E Michelins.
 

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Did Gypsy leave the building?

RT made a great suggestion on how to maximize fuel economy.

Buy a ScanGuage-2 and you can see real time MPG.

There are times I improve MPG by downshifting to next lower gear rather than having lower RPMs in taller gear.

Last fill-up: 19.4 mpg 503 miles.
 

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I ordered my 1999 E350, 7.3, in 1998 and took delivery in December, '98. Next month, it's 21 years old, old enough to drink, and has 140k miles. Initially, it got 11 mpg, maybe the weight of the Companion Van conversion and the high top had a lot to do with it. It got 9-10 pulling a 10k pound, 36 ft travel trailer. I've done a lot of mods, am an old guy driver, and have never consistantly got above 15. I retired it in 2012 and it stays in the garage except for maybe a weekend trip. I now tow with a 2012 F350, 6.7, that I bought new in 2012, and am seeing the same mpg. 10 towing, 15 on the road, if I'm lucky. Both vehicles have the best maintenance, performance mods, synthetic fluids throughout, TPMS, and fuel economy stays the same. Based on all this, I am a little suspect of high mpg claims; LOL.
 

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I'm in the 12 to 16 MPG club (and the 16 is only seen on road trips when I get on the long flat highways & try to keep speed to 65 or less. There is also certainly some logging errors associated with just how hard I try to top the tank right up to the filler neck at fuel stops when I am tired & don't want to stand there & play around with that. So I might calculate out 16 MPG once in a while BUT that's probably because of the difference between amounts of fuel through the various fill ups. PS: I'm not sure about the Scan gauge II giving "real time" MPG. IIRC that was also just a math equation based operation that required a number of fuel fillups and entering gallons... into the Scan gauge unit. IE: I don't consider that "real time" fuel MPG or usage. Just a best guess estimate of usage bases on past figures entered into the unit. (I could be wrong but that's the way it seems to me). IE: If you floor the throttle pedal does the scangauge suddenly read out 5 or 6 MPG?
Anyway, Just so you guys out there won't feel as bad as I do when I hear all this "I get 17 or 19 MPG" ... stuff, I run with a pretty good load/weight (got a lot of sh#$ in the back of the van) but not #3000.
And i'm lucky to see 14 - 15 on a regular day to day town & highway average between fill ups. There are MANY factors & variables in most peoples day to day driving so pinning it down to one MPG number is just not realistic. PS. My van uses Georgia Overdrive whenever possible! But in my local area there are not many hills/mountains so that's mostly a road trip thing. (bet some of you are goggling Georgia Overdrive right now) LOL . So don't feel so bad guys. Not everyone is getting those unbelievable MPG numbers you read about. And I don't get the impression that most of the guys on this forum are driving around like a bunch of 90 year old ladies either, so that's another factor that's going to make those 19 MPG numbers just a dream.
BEST idea I heard so far is the one from (was it RT about getting the tow bar) LOL That was great! Good one! I hear tell if you have roof racks you can install a wing shaped device that creates more lift than drag & reduces vehicle weight at highway speeds thus giving much better MPG. Add that one to your list of Mods. boys!!! DDT
 

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The SC2 has two separate readings for MPG. One is an average but I don't know how many previous miles/minutes it averages.
The second is quite close to "real time" meaning that it immediately changes according to fuel demand; however, as you recalled, it is dependent on past reports of miles logged and gallons used at fill-ups. I have mine dialed in so that it reports within close tolerances. It is an excellent device to see MPG at different RPMs and I choose my gear accordingly.

I will try and take a short video and add it here later today.

Ofcourse, the SC2 offers so many parameters that this is only one benefit.

EDIT:
I actually do drive around like an old man. I practice the philosophy that the best fuel economy comes from always driving like you have your dog in the front seat with his head out the window...nice and easy.
 

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When I first got my Scangauge II the MPG feature was something I was interested in too. But it seemed kinda
complicated following the directions of how to do it....Fill up, drive around, fill up again, enter gallons, enter miles...Repeat ... But the problem was if you messed up one of the entries (Or hit the wrong button at the wrong time), there didn't seem to be any going back to fix it. I tried a couple of times & then just said forget it. It's easier to just do the math when you fill up. I always reset the trip odometer when I fill up.
I too drive around like an old man these days.(probably because I am one now), I still can't get any better MPG.
But I'm not really doing anything special to attempt getting it either. I also have little bit oversized tires so what way does that make the MPG math go? Better or worse? I forget.
Anyway, I just saw so many posts with the Higher MPG numbers, I thought I would add my number to the mix for those that thought they might be the only one.
 

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Scan gauge isn’t that hard to calibrate. You fill up. Hit more, fill up, save. That zeros it out. Drive for a while- the lower you run your tank, the more accurate it will be. The fill up again preferably using the same nozzle and cutting off the exact same way. Hit more, fill up and then adjust your gallons to what the pump said. Hit save and your done. No miles or anything to adjust. My lifetime average is 18.8 mpg. That’s towing, city, highway - everything.


Sent from my iPad using Tapatalk
 

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Sounds like I need to look at it again RT and have your instructions in front of me.
What you just wrote in 2 sentences I think the SG directions took 2 paragraphs to describe.
(no wonder I gave up). Thanks for the input. I'm going to write that down & give it another try. DDT
 
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