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7.3l mileage

3K views 20 replies 11 participants last post by  TRUKPULR 
#1 ·
Occasionally there is a thread about mileage so I thought I would share some results from a recent trip.

I have a 2003 F350 CC 4x4 FX4, 7.3 auto, 4.10 gears. The truck is completely stock with the exception of 285-75-16 tires instead of the factory 265's. I also have a canopy.

I recently made a trip from Lafayette, LA (altitude 5') to Farmington NM and up into southern Colorado by the Navaho State Park (elevation 7500'). I left Lafayette with a mileage of 13.8 mpg (averaged over several months, I did not reset the mileage either). By the time I was in western Tx my mileage had increased to over 14. By the time I got to Farmington it had climbed to 14.7 mpg (remember this is averaged with the 13.8 from before). I drove around the mountains for 2 weeks before driving home. I reset my mileage when I fueled up in Farmington. I started the trip with 16.7 mpg (alt 7400', 81 F). I filled up again somewhere in west TX and again east of Dallas. By the time I got to Dallas my mileage had dropped to 15.3 and by the time I got back home in Lafayette it was right back at 13.8 mpg (the temp in Laf was 81F as well....overcast).

So what gives? Is it all the change in humidity? Colder air @ 7400' has more oxygen then warmer air @ sea level? It wasn't even warmer when I got home but alot more humid.

At first I thought maybe it was the fuel but the mileage dropped continously throughout the entire trip.

The whole trip was about 2800 miles so it should be a good representation I think.
Any thoughts..
 
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#2 ·
Ford could save up diesel techs a lot of grief by not putting those damn milege computers in the trucks.

Mine gets to 1/4 tank I fill it up.

Have no clue what it gets.

I'm not rippin' on ya, there is a reason they dont put the fuel economy numbers on the window sticker on 'em though. :wink:
 
#3 ·
Well I used to get over 18 when I lived in Canada. Obviously after driving it for 5 years it hasn't bothered my too much. LOL. I am more interested in why the decrease. Is it fuel, location, weather, or is there something wrong I should be fixing.

The mileage is going to be what it is going to be and I need drive it to work no matter what it is so......
 
#4 ·
One other note. I did suspect the overhead calculator was incorrect after I changed my tires last fall so I hand calculated my mileage for a couple months and came up with the same numbers.
 
#5 ·
well they do call those things lie-o-meters, you might have been getting the same mileage the whole trip but the computer was calculating it different due to differences in Alt. most of the time mine is pretty accurate too, but one time it read 26mpg (2000 F250 scab long box 7.3 4x4) when I calculated it I actualy got 19, which is a little better than my average 16-18 but still no where near the 26 the meter was reading. Next time I reset it and ran it went back to reading 18mpg and when I hand calc the mileage it was within a tenth no idea why it did that but on occasion I will find it do something really strange lke that, might be the fuel is different or the air but it will do it on occasion.
 
#6 ·
That thing lies it's *** off...... It's not accurate. I think it MIGHT be accurate for the given moment, that's it. I've got an 01 F250 2WD C/C Lariat. The 7.3 has 263,000 miles on it

Now Jay, I live in New Orleans. I've been averaging 19 mpg back and forth to work. I live in Marrero and work in Covington. I occasionally drive from Marrero to Port Fourchon for work too. Mapquest it, it's a good mix of city/hwy driving.

I recently made a trip to Cameron from Marrero. I fueled up in Lobdell (second exit west of Baton Rouge). I then drove from there to Cameron, back home and then to work and back one time before I had to fuel up again. I got 21, almost 22 on that one (530 miles)....

My mileage just picked up since the weather warmed up and I started keeping it at or below 70 on the highway. I'm running the 90hp Diablosport Predator tune as well and getting those numbers. It'll drink the fuel down if I put my foot in it, but driving it normal will get me 19 or more MPG.

One thing you may want to try is getting a good code scanner and scan the truck. I had some bad/biased sensors that did not ever trip the SES light. I just found them by asking richter69 about them and the guys over at www.fordtrucks.com

I changed the IAT sensor, cleaned the EBPV sensor, switched to Rotella 5W40 Synthetic oil and recently serviced the differential. I'm sure the synthetic switch did nothing, but it helped with the cold morning chugs....

I will recommend this.... Change the diff fluid if you have never done it. Don't believe the Ford manual saying never service it because it has synthetic fluid in it. It's a crock... I popped the cover on mine and it was the nastiest smelling stuff I've ever put my nose near. It was completely burnt, low and had crap floating in it. I think the clutches are shot, to say the least. I'm pricing out a rebuild today..... Hopefull it's a pull and rebuild type deal like an 8.8......
 
#9 ·
The ulsd issue I resolve by running biodiesel, running B99 approx right now, but in the winter i also just add the additives. Winter mix fuel will decrease your mileage even more.
But the big one you mentioned is the sensors look for codes 0470 and I think its 0472 both relate the the EBP sensor (exhaust back preasure) cleaning the tube and sensor helps sometimes but in my case the sensor was bad and this code does not set the CES light. I replaced my sensor and gained 2mpg and a lot of lost HP back
 
#12 ·
richter69 said:
I replaced my sensor and gained 2mpg and a lot of lost HP back
All the EBPsensor does is tell the pcm if the position (more or less) of the exhaust back pressure valve, any performance of economy difference should not be directly related to it.
After talking with a couple different people that do the programing for tuners and an extended talk with Jody of DPTuner, thats a wrong assumption the PCM actually changes fuel delivery tables and will defuel the engine if it determines there is too much exhaust back preasure to try and bring that figure back inline with what it is expecting. High exhaust back preasure is what the PCM reads when that sensor goes bad. It basically drops to the same fuel table as when it reads overboost situation defueling trying to bring the preasure in line with that it believes it should be.
There was a noticable increase, I drove mine on a set run, max boost was 28psi, changed the sensore and back on the same run and pulled 33lbs of boost...doesn't sound like a non issue to me, that was with no other changes, same day about 1/2hr apart on the runs.
 
#13 ·
mpg's

Diesel is a heat, humidity, temp, alt, water (condensation), additive, quality, sensitive fuel. Any of these factors can alter your mpg's, especially the temp factor. Heat makes diesel molecules expand way much. This will reflect in your mpg.
The heat I'm talking about is the temp. the fuel is when you fill your tank. If your station uses above ground tanks in the South, you are really getting "hot" fuel. (Which is common in the South + South West!)
When diesel is pumped from a tank with the fuel at say, 90 degrees, you are not getting 100 gallons of fuel when that's what the pump reads. You will actually pump 60 - 80 gallons of fuel. This is what is referred to as temp. compensated fuel. Only computerized pumps can dispense temp. compensated fuel / gas, but only if the pump owners have that feature turned on, on the pump.
This is a very simple explanation of a very technical situation.

There is a group suing some fuel marketers now for selling "hot" fuel. They are trying to make this an all encompassing lawsuit which will have a profound effect on all fuel marketers in the USA.

Fuel up diesel in the early am's to reduce the heat factor in diesel.
 
#14 ·
Well I get to thinking along the lines of the pre SD trucks too much, the EBP has no effect on fueling on those, the SD trucks it might to some degree, but the pressure would need to be a good deal out of spec in order for it too happen.

The 08's are a mother to work on.
 
#15 ·
Jon your right the preasure does have to be really high but if the sensor goes bad the sensor goes high limit plus so it definatly does affect it. It reads higher than if you have a cat truck and the cat plugs up (which as I understand it is the reason for it to do that). I am not sure on the pre superduty trucks how it all works, just on mine.
I have seen the mess with teh 6.4, like having to remove the entire cab to service or replace the high preasure pump :shock: After looking at stuff like that I determined I was just gonna keep my 7.3 till the day they put me in the ground, heck I got a good one early enough to still have forged rods. :lol:
 
#16 ·
FWIW, I have an '01 SD, CC, 4x4, 6-speed, 3.73 gears, and 285 BFGs with 159,000. I get anywhere from 15.5 to 20 MPG. To get 15.5, you drive back from Owensboro, KY to AL at 95 MPH. To get 20, you drive to Owensboro, KY and back at 55 MPH and get 20 MPG, (621 miles on a tank, 31-32 gallons). Normally, I drive 60-75 and get 17-18. I have a DP tuner chip by Jody Tipton and it did not help the mileage any. The economy 80 hp setting runs good, the towing setting, is ok, and the extreme sucks. It slows down on extreme. I don't know how people have a "140hp setting". I can't feel any more power after the 80hp economy setting.
 
#17 ·
Heat makes diesel molecules expand way much.
What?

Heat doesn't make liquids expand. It makes gas expand. So until diesel reaches it's gaseous state, it won't matter. It may very well mean the fuel mixture detonates earlier when it's compressed in the cylinder. But you're still getting the same amount in your gas tank.

well they do call those things lie-o-meters, you might have been getting the same mileage the whole trip but the computer was calculating it different due to differences in Alt.
Not at all. As long as your tires are correctly sized, the "lie-o-meter" knows EXACTLY how much MPG your vehicle is getting because it knows how many milliliters are going into each cylinder, and how fast the wheels are spinning. That's all it needs. Your MPG changes constantly. What you see at the pump is merely your averaged out MPG.

So what gives? Is it all the change in humidity? Colder air @ 7400' has more oxygen then warmer air @ sea level? It wasn't even warmer when I got home but alot more humid.
Colder air is denser. And high altitude air is less dense. Humidity also cools the mixture because water molecules absorb heat as they change from their liquid phase to gas phase (poor man's water injection).

The first two don't actually affect your MPG except for the possibility of slight efficiency changes.* The third may be a factor as heat = expansion = force on the piston. And absorbed heat may reduce that.

However, I think the most reasonable assumption is that it was you. Either you subconsciously drove differently OR, because the air was thinner, you kept the same throttle but recieved less and less power gaining MPG. And it was so gradual as you went up into the mountains that you didn't notice.

My 1990 2.0 (naturally aspired) Eagle Talon when taken up the North Carolina mountains can't even get above 60 MPH at WOT. When I get down the mountain, I can hit 115 MPH. There's just not enough air up there. And while you didn't experience anything that drastic of a power change, your engine dwarfs my little Talon so you don't run at WOT all the time.
 
#18 ·
Sorry, but fuel DOES change density as temperature changes.

Hotter fuel has a lower specific gravity than cooler fuel.

When we fill up the Jet with Jet-A, we measure the weight of the fuel, not the volume. This is to make up for dramatic temperature changes of the fuel as altitude changes. It might be +30C on the ground, but it may be -30C up at altitude.

So in the truck, a gallon is not really a gallon. It's a convenient way to measure the weight of the fuel, and it is close enough for 99.99999% of us. Me included!

But the truck does not burn volume, it burns weight. So if it's hot, that gallon of fuel weighs less. So, it takes more gallons to get the same number of pounds of fuel into the engine, and therefore the MPG goes down. The pounds per hour will stay the same.

Greg
 
#19 ·
Novous said:
Heat makes diesel molecules expand way much.
What?

Heat doesn't make liquids expand. It makes gas expand. So until diesel reaches it's gaseous state, it won't matter. It may very well mean the fuel mixture detonates earlier when it's compressed in the cylinder. But you're still getting the same amount in your gas tank.
Really, are you sure of that? tempature does make liguids expand and contract, take water for example it contracts up to the point of turning into a solid then expands again. If you doubt heat doesn't make liquids expand then take some vegetable oil and put it into a pan and heat it, I say use oil cause first it's very close to the same as diesel, second it's not like water it won't start to boil at 212deg. I do this all the time when I heat oil up before putting it into my processor for turning into biodiesel, I can put in 4 gallons into the large stainless cooker, from room temp to 250degs it rises in the cooker approx an inch but according to you thats my imagination I guess.
 
#20 ·
dammit, we got some smart sombitches out there.guess ive been to busy fixin piece of S!!T 6.0L and dreading working on the piece of S!!T 6.4L im to tired to think of crazy fuel/oil expanding in tanks affecting fuel economy.im going to go hug both of my paid off 2000 superduty's.we need to come up with some catchy logo for the 7.3L.like our thank the lord for the big block ford. kinda like WHAT....NO 7.3,YOU'VE GOT TO BE S!!TIN ME! i like that one best so far.later
 
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