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Old 10-12-2020, 09:48 PM   #11
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I have a very similar setup....2008 4x4 5.4L 3.73 gearing and 285/70-17's.


I have not been able to use any programmers to get my speedometer calibrated, and it reads just about 10% high...when it says 40mph I'm doing 44 and when it says 60mph I'm doing 66.


Since the odometer is also reading 10% low, the calculated fuel economy is going to be 10% low..so if I calculate 10mpg, I'm really getting 11 mpg. The mileage shown on the odometer is also 10% less than the miles actually traveled as well.


I find that depending on how fast I drive I get 11-12 MPG.
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Old 10-13-2020, 06:39 AM   #12
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I have a very similar setup....2008 4x4 5.4L 3.73 gearing and 285/70-17's.

...Since the odometer is also reading 10% low, the calculated fuel economy is going to be 10% low..so if I calculate 10mpg, I'm really getting 11 mpg. The mileage shown on the odometer is also 10% less than the miles actually traveled as well...

That's a point often missed when calculating fuel economy on a re-geared rig. Your 'miles driven' can be 10% greater than you are giving yourself credit for. Using percentage is a great way to normalize this before calculating fuel economy (FE). I use my GPS, you can use a phone gps as well, but I've not done it myself.


When you (or the guy who built your rig) added larger diameter tires for ground clearance, you also re-geared it. Not intentionally, but in effect. Ford figured out how to squeeze the best balance of performance vs fuel economy by selecting axle gearing that matches the engine's sweet spot (rpm range for optimal efficiency) so the sticker on the side of the van was most attractive to the buyer.





The other points often missed is a lifted 4x4 van is the exact opposite of what you'd do if you wanted better FE.



Here's the 'big hitters': Wider softer tires w/offroad tread. Increased gap under body, effectively increasing the frontal area. Increasing the air turbulence with all the add on stuff, racks, bull bar bumper, soon to be pop top. I race at Bonneville and all that little shit adds up and matters, it matters more as speed increases.



If it were me I'd keep building it out the way I wanted it, pop top, leave the rack, add a ladder, LED light bar, awning, all the stuff that makes it a great camping off road rig, consider re-gearing both axles and adding a posi-traction diff to the rear (while your mechanic is setting up the R&P) if it doesn't already have one. Add an auxiliary fuel tank mounted to the frame rails w/transfer pump, and a dash switch, or some similar system to extend your range in Mexico and everywhere else. Drive 60-70, and budget gas $$ for each trip, have fun!
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Old 10-13-2020, 07:07 AM   #13
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Honestly, 10 MPG sounds good. The problem is you're pushing a big brick down the road. The faster you try to push that brick through the air, the more horsepower you'll need and the more fuel you're going to use.

Bear in mind, the E-series van was designed in the 55 MPH era and that is the speed they were optimized for. Adding a lift and big tires only worsens the effects of higher cruising speeds.

It might also help to remember that when bone stock, these vans only got in the mid-teens for MPG at best. Many years ago, my much lighter and lower 1990 E-150 with a highway optimized 5.0 EFI 2WD drivetrain could only manage 17 MPG on a good day at 60 MPH. If I tried to go much above 60 I could practically watch the fuel gauge needle move.

According to the previous owner, my 7.3 IDI E-350 can get 20 MPG on the highway. If I add a Weldtec lift and larger tires, I am anticipating 15 if I'm lucky.
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Old 10-13-2020, 11:37 AM   #14
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Originally Posted by boywonder View Post
I have a very similar setup....2008 4x4 5.4L 3.73 gearing and 285/70-17's.


I have not been able to use any programmers to get my speedometer calibrated, and it reads just about 10% high...when it says 40mph I'm doing 44 and when it says 60mph I'm doing 66.


Since the odometer is also reading 10% low, the calculated fuel economy is going to be 10% low..so if I calculate 10mpg, I'm really getting 11 mpg. The mileage shown on the odometer is also 10% less than the miles actually traveled as well.


I find that depending on how fast I drive I get 11-12 MPG.
My van is originally from Canada, so the speedometer is in KPH....so I don't pay any attention to it. I base all my speed and mileage calcs from phone/head unit GPS readings (in miles/MPH).


Also, is there a standard size fuel tank you end up with on a UJOR conversion after trimming the tank? From running the tank down to empty, then filling it up, it seems to be right around 29 gallons, but I've seen other people claiming to have 31 gallon tanks after the 4x4 conversion tank trimming.
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Old 10-13-2020, 12:18 PM   #15
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Get a spare tire tank and go up to 50 gallons. Then you can make it almost 500 miles between filling.
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Old 10-13-2020, 12:54 PM   #16
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Honestly, 10 MPG sounds good. The problem is you're pushing a big brick down the road. The faster you try to push that brick through the air, the more horsepower you'll need and the more fuel you're going to use.

Bear in mind, the E-series van was designed in the 55 MPH era and that is the speed they were optimized for. Adding a lift and big tires only worsens the effects of higher cruising speeds.

It might also help to remember that when bone stock, these vans only got in the mid-teens for MPG at best. Many years ago, my much lighter and lower 1990 E-150 with a highway optimized 5.0 EFI 2WD drivetrain could only manage 17 MPG on a good day at 60 MPH. If I tried to go much above 60 I could practically watch the fuel gauge needle move.

According to the previous owner, my 7.3 IDI E-350 can get 20 MPG on the highway. If I add a Weldtec lift and larger tires, I am anticipating 15 if I'm lucky.
I can confirm those 7.3L diesel numbers. My first van got 19-20 MPG when it was empty and stock. Once I added a pop-top, lift and tires I got around 14 MPG.

On my new van that I just drove home from Colorado I got 18 MPG and thats with the CCV pop top on it. Getting it back from weldtec soon and I expect that to drop down into the 13-15 MPG range.
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Old 10-13-2020, 01:39 PM   #17
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Get a spare tire tank and go up to 50 gallons. Then you can make it almost 500 miles between filling.
Sounds like a good option, depending on price
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Old 10-13-2020, 01:56 PM   #18
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Regearing my E350 from 3.73 to 4.56 was the best mod I did to it. Didn't help mileage any - but sure made it a lot more driveable. Much more responsive and, I'm thinking, probably a lot easier on the whole drivetrain. No longer seems to be straining to maintain the speeds I want. Not just that, but when going down a really steep trail, 4-Lo now helps with engine braking whereas before the van just seems to freewheel.
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Old 10-13-2020, 02:05 PM   #19
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I was getting 14-16 when my E350 was stock. Now, with 285/17ís, Agile 4WD, Poptop, house batteries, flooring, and some build-out, Iím getting 10-11mpg and occasionally squeak out 12. And thatís with the calcs Boy Wonder talked about. I expect to go down farther as the weight increases with further build. Itís gone from 6350 to 8000 currently. I pretty much stick to 55mph or 60-65 out in the boonies.

I think the description of us driving a brick is a good one. I try to ignore that.
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Old 10-13-2020, 08:12 PM   #20
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I am getting 11.3 mpg on my 2010 5.4 with 4.10 gears running 305/65r18 and I don’t drive for economy. As mentioned, With taller tires your distance traveled is more than the odometer reads. Make sure your alignment is OK, Specially toe-in and that the steering is tight. I had my tie rod loose and my mileage went down to 10 as the steering was vague and the constant corrections.
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