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Old 12-22-2012, 03:31 PM   #1 (permalink)
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Ford Expedition- engine load theories, opinions??

So, I drove the gas hog the other day (2000 Expedition, 4.6 4wd) and decided to do a little data logging. Upon looking at the plots one thing immediately jumped out at me, at cruising speed the engine loads seem very high.

The Expedition is geared very tall from the factory. At 60mph it turns about 1600rpm with it's 3.55 axle ratio and uber-tall OD. At a steady 50-55mph cruising speed the engine load was hovering right around 60%. Now, this seems nearly ideal except for 2 things:
1) there is virtually no headroom should you encounter something like a hill, a headwind or something else. The difference between 60% and 90+% (and going into fuel sucking open loop) is like 1mm of pedal travel or a 1% grade change. With a vehicle of this size it seems that a little more headroom for changing conditions would produce a better average mpg at the sacrifice of mpg's under all out ideal-conditions (straight flat road with no wind).

2)Only the SLOWEST of slow accelerations keeps the engine load below 80%. Now, I drive like this most of the time anyways but once again, there is no headroom for things like accelerating uphill or carrying a load. It is insanely easy to get the load spiking over 90%

Do any of you think that there might be better average mpg's to be had by going to a shorter ratio (say, 4.10 axle)? It seems that it would keep the engine load down a little more and keep it from going into open-loop at the first hint of an elevation change (where it currently drops from 4th gear IMMEDIATELY). That little 4.6 just seems like it needs a little more gear to pull around that heavy truck.

My brother swears up and down his old F150 (same drivetrain) picked up a couple of mpg when he switched to a shorter final drive. I tend to take his opinion with a grain of slat a lot of the time though as I don't trust his methods for calculating mpg.

Any thoughts?

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Old 12-22-2012, 03:50 PM   #2 (permalink)
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My F150 with E4OD downshifts at the slightest provocation too, and it really makes me mad. Back in the day I tried larger diameter tires but that was a fail. Stock size tires are the best. The piston speed calcs for it put it at too slow rpms at 55 so it may very well be that shorter axle gears would help. Mine's 4x4 so I won't be doing that.
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Old 12-22-2012, 05:06 PM   #3 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
My F150 with E4OD downshifts at the slightest provocation too, and it really makes me mad. Back in the day I tried larger diameter tires but that was a fail. Stock size tires are the best. The piston speed calcs for it put it at too slow rpms at 55 so it may very well be that shorter axle gears would help. Mine's 4x4 so I won't be doing that.
Yeah, your choices are: lose 20-30mph going up the slightest hill by trying to convince it to stay in OD (in which case you may end up going so slow that it has to downshift anyway) or let it downshift and send your mileage straight into the crapper.
If you figure it up, to get into the middle of the proper piston speed range you'd have to be going like 75mph.

I really think this truck would respond well to 4.10's (ESPECIALLY with the camper in tow) but that's an expensive endeavor to change ring and pinions in both ends (4WD), even doing it myself, with no guarantee that it won't cost you mpg's (it's bad enough the way it is!).
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Old 12-22-2012, 05:15 PM   #4 (permalink)
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I would focus more on coasting than acceleration. from my experiments (i just posted a thread) differences between 60% or 80% load acceleration are minor, specially for long distances (ie. merging onto a highway). for shorter distance such as 2 stop signs 300ft apart i would use as little engine load as possible.

i have a 4.11 final drive on my subaru and my rpms are a tad bit high -> 3000rpm at 70mph. however my engine load is fairly low at that speed, only 40%. with this i can easily get 37mpg easy just by using cruise control. so for cruising i think lower engine load is better as well, but again this is for my car. i know alot of auto enthusiasts swear by high load and lower RPM but that hasn't been the case for me in the real world. my car has an oversquare engine design which makes it rev happy. your 4.6 is a square design which i'm not sure about. my v6 TL is square and likes 1800rpm with 40% load. so it depends on the car but a 4.10 axle will surely degrade your fuel economy. At the same time 4.10 axle will make the car better performance wise. i would get a 4.10 axle for towing and 3.55 for fuel economy.

Last edited by ever_green; 12-22-2012 at 05:55 PM..
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Old 12-22-2012, 10:07 PM   #5 (permalink)
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that's a high load. could there be something wrong with the engine?..when i was pulling a trailer and my bike in it (1100 lbs) i was at about 75% load at 55 mph getting 32mpg
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Old 12-23-2012, 07:58 PM   #6 (permalink)
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When you are geared for mileage you DO NOT accelerate uphill. That 60% load is near ideal for cruising with mileage.

Learn to DWL. If you take the time to get good at it, you will be amazed at how well you can hold speed without downshifting.

That, plus DWB to better use your inertia.
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Old 12-23-2012, 08:22 PM   #7 (permalink)
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It's a lot of vehicle with not much motor. Conceivably a larger motor would do just as well for mpg, but with a better reserve of torque, for the FE minded driver. This was a common dilemma in the 1960's about travel trailer towing. The advice was generally to go for the biggest motor and drive with a lighter foot. Because when it came time to work the vehicle (heavy trailer and grade ascents) the mpg penalty for a 440 over a 383 was minimal.

The alternative was to re-gear the 383 higher than normal factory choice axle ratios (3.23 for the sedans & wagons). 3.4 or 5 0r 6 was in the ballpark as 3.73 was getting too high, but it was about the only choice. The 440 produced more torque at a given rpm so it became the best choice for a 6-8k TT. The 383 could do it, but at 500-rpm higher which made it more temperamental.

Choose with care. Use an online calculator to see gear change effects. Lay out the stock ratio versus rpm & speed and then do the same with contemplated choices.
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Old 12-23-2012, 11:33 PM   #8 (permalink)
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ive had it in the back of my head what it would be like to put the 4.2L V-6 and manual trans from a 1/2 ton in a Expedition

i know it woudent go any faster at all.
but there both 1/2 autos so the swap woudent be that hard...
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Old 12-24-2012, 05:40 PM   #9 (permalink)
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Quote:
Originally Posted by JRMichler View Post
When you are geared for mileage you DO NOT accelerate uphill. That 60% load is near ideal for cruising with mileage.

Learn to DWL. If you take the time to get good at it, you will be amazed at how well you can hold speed without downshifting.

That, plus DWB to better use your inertia.
Not all stop signs/lights have a straight/ flat road in front of them. There are times when it is necessary to accelerate uphill. I try to avoid it as much as possible though. Often times I attempt to keep load constant when on hilly roads and just let my cruising speed drop as I go up and pick up as I go down. At that though, it's not uncommon to lose 15+mph going uphill if it's significant enough. If you're starting out at 50mph that means you're down to 35 at the top and you're out of the range of OD and the tranny is going to shift to 3rd. I've gotten pretty good at working it just enough to keep it in 4th with lockup but it's tough as this thing wants to downshift at the first sign of a hill.

My point was that even under normal conditions with a conservative driver (me) engine loads go high enough at low rpm to make it go into open loop. Under ideal conditions (straight, flat road) I'd say it's geared perfectly but in the real world I'd say it geared too tall. Since 95% of the time this vehicle is used under less than perfect conditions (it seldom ever sees wide open highway for miles on end unless it's has a camper in tow) I believe there might be some mpg to be had from a shorter ratio. I was curious as to everyone else's thoughts though.



Quote:
Originally Posted by trooper Tdiesel View Post
ive had it in the back of my head what it would be like to put the 4.2L V-6 and manual trans from a 1/2 ton in a Expedition

i know it woudent go any faster at all.
but there both 1/2 autos so the swap woudent be that hard...
I've wondered that as well. My Dad used to have an F150 with the 4.2 and a manual trans (ext cab, short bed) and not only did it run surprisingly well, it would get 23+mph in mixed highway with a driver than knew NOTHING of hyper-miling.
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Old 12-24-2012, 06:02 PM   #10 (permalink)
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Quote:
Originally Posted by slowmover View Post
Choose with care. Use an online calculator to see gear change effects. Lay out the stock ratio versus rpm & speed and then do the same with contemplated choices.
With a 4.10 ratio and the factory .71 overdrive it would be running right around 1900rpm at 60mph. Probably less than ideal for open highway (it's still within the "butter zone for piston speed, I believe) but it may allow towing in 4th w/ lockup. As-is you HAVE to lock it into 3rd with a trailer of any size in tow or else transmission burn-up will be inevitable as it hunts all over the place for gears/ TC lockup. Fortunately it is eager to lock up in 3rd (and will pretty much stay there) but mileage is horrendous with the TT in tow.

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