A big factor in MPG for '99-up 7.3L PowerStroke pickups is luck of the draw. Some can get up to 20 MPG cruising at 65 MPH on the flats with no load in/on the truck. But most will get about 16 to 17. And my unlucky draw meant mine got only 15 to 16. I tried every trick in the book to improve MPG, but the only thing that worked was to slow down and put a raw egg on the go pedal. I had tunes from three different well-known tuners, including economy, towing and 120 HP performance tunes, and none of the tunes improved my MPG.
Almost always, when some guy spouts off about better than 20 MPG, you can bet he's either relying on the lie-O-meter in a Lariat, or he doesn't know how to accurately manually calculate MPG.
To do it right, you must fill the tank to the cap with liquid diesel - not foam - both before and after you make your mileage run. That requires about 10 minutes after the automatic pump first shuts off - and with some pumps such as Flying J you'll probably give up before you get the tank full. And you must have a calibrated tripmeter with less than 1% error.
To see your tripmeter error, drive 100 miles on an interstate highway without crossing a state line or changing highway numbers. Reset the tripmeter to zero with your front bumper on a mile marker that's not near an entry, exit, overpass, or anything that could cause the highway crew to not place the mile marker where it belongs. Drive 100 miles per the interstate mile markers, reading the tripmeter when your front bumper passes the 100th mile marker. If your tripmeter doesn't read between 99.5 and 100.5 miles, then you need to change the tire revolutions per mile parameter in the ABS module, using a scan tool that can access the ABS module.
How much to change the revs/mile parameter? By the same percentage as your tripmeter error. Common error with stock-size tires is about 2.5%. For mine I was running stock-size Michelin XPS tires, and with my revs/mile parameter changed to 650 my tripmeter was 99.7% accurate. That's close enough for Government work. But most people don't have LT235/85R16 tires, so their required revs/mile parameter to have an accurate tripmeter will be a lot different than 655.
My Sierra Blanca in the sig pic was a great pickup for 11.5 years. I sold it a coupla years ago. I drove a hand-me-down 2003 F-150 SuperCrew 4.6L 2V for a while, but it was unacceptable for towing more than a rowboat. Replacement is a 2012 F-150 EcoBoost SuperCrew Lariat that tows my 5,000-pound TT like a dream.
Last edited by SmokeyWren; 01-26-2013 at 08:51 AM.