2000 F150 MPG question

[Shomeyrwit]

Driving a long bed supercab f150 2wd 4.6l auto.

when I bought this truck the first few tanks were returning 19mpg on my 20mi each way hwy commute. Since that was the same as the 6cyl minivan and only 3 less than my girlfriends Acura cl (6cyl) I got all curious about breaking into the 20+ mpg range (which hasnt happened)
So I tuned it up which it didnt really seem to need and set off on base line mpg runs, 3 days driving the same exact route at the same speed filling up to the same level at the same pump at the end of the day and was happy with a 19.1 avg, the next week I started monday with a full tank and drove that tank till friday and was again plzd with a 19.2 avg.
At this point I started checking every 3 days and was suprised that the more careful I tried to be accelerating the worse the economy got, but was still ok with above 18.5 averages.
The real shocker was my in town mpg. on the weekends I stay around the neighborhood and was checking this mpg vs my work commute, this is all surface street max 40mph driving lots of stop signs and lights. Driving normal produced an avg of 16.6mpg, driving as insanely carefully as I could and not get run off the road neted 14.4????? so I tried again and got mid 14's and a third time only a 14.8 ??? so I decided to romp on it without mercy and was rewarded with 15.5 and a 15.0 and there was no third test because I only have so much nerve and tickest cost to much.
So if your still with me why would being super cautious and accelerating slowly net less than practically street racing light to light???

my current mpg per tank is between 16.8 and 18.3 which is not bad considering that all the orig mpg testing was done on 225/70 15's and the truck currently has 255/70 16's on all four corners. The plan was to run 235 75 industrials but money and availability (and the 16 yea old that still lives in my head and thinks big tires and loud exhaust rule) have conspired agin me

[The Atomic Ass]

There's a balance to be struck with an automatic. On the one hand, tromping it raises the engine RPM's, which wastes fuel. On the other hand, the engine is most efficient near wide open throttle, and the closer you get to closed throttle the less efficient it is.

The balance I've found for most ~4L engines with automatic transmissions is to accelerate as hard as possible while keeping the revs around 2K, or 2.5K for looser torque converters that are usually equipped in 4WD and AWD transmissions.

Also, accelerating to 45 instead of 40 may yield more benefits, if it is possible to do. Most automatic transmissions will lock the torque converter at 45, dropping engine RPM's substantially.

[comptiger5000]

My Jeep gets best FE if you shoot to let it shift around 2100 or so. It picks up much faster than at 1900 - 2000, and allows you to give it a good bit more throttle.

[Shomeyrwit]

hmmm very familiar with the efficient at wot concept , doin as much work as it can do with whats availible,,, had a 72 f100 with a 360 2bbl usually got 12 to 14, swapped in a 401 hp mech lifter 390 and once I quit putting my foot in it would get 16 to 18 (usually 16) on the highway, my mech explained the enough power to push it around vs lug it around concept,,, with lots of expletives,, but that was my introduction to more power meaning better FE , always makes me wonder when people detune engines for mpg, cleary can work but to me the other option is better

[Domman56]

Check all your filters and fluids and everyting plus make sure those tires are aired up to max pressure before attempting FE readings