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Bomb Technician.
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Discussion Starter · #1 ·
I noticed tonight that my truck is using just waaaay to much fuel, even at idle. I had to drive 30 miles to pick my uncle up and when i left out i had a lil over 1/4 a tank. i drove 60 the whole way only got stopped at one red light. when i pulled into the parking lot at his work i was a little under 1/4 a tank.

well i sat there for about an hour waiting for him to get off work and right as he was coming out i noticed that my low fuel light had came on. I know on a full tank im lucky to get 200 miles out of it. usually i get about 170-185 miles on a 16 gallon tank. Ive changed the oil airfilter plugs and cleaned the tb. im at a loss here. wheres my fuel milage goin?
 

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The Anti-RUB
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That seems a bit excessive for even a tune-up to fix. I'd check for leaks in the tank, fuel lines and fuel rails/injectors. My bet is fuel lines. Should be easy to find with a good nose. Don't use a lighter or match while searching, btw. :jester:

btw, my D came stock with a 25 gallon tank.
 

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Dak-Dur 11th Most Wanted
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Can't tell you anything until you have solid numbers. "just over 1/4 tank" and "just under 1/4 tank" mean nothing. Also everyone's fuel light comes on at different times.

You need MPGs to know anything. And not from the overhead computer. Need to do the long division.
 

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Bomb Technician.
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Discussion Starter · #5 ·
im not leaking fuel anywhere, id smell that. exhaust smells fine. Ive got all my tires set at 35psi. What tire size came stock on the 2000 4x4 v8 daks?
 

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Bomb Technician.
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Discussion Starter · #6 ·
Can't tell you anything until you have solid numbers. "just over 1/4 tank" and "just under 1/4 tank" mean nothing. Also everyone's fuel light comes on at different times.

You need MPGs to know anything. And not from the overhead computer. Need to do the long division.
last tank was 11.26 mpg my truck wasnt blessed with an overhead.
 

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Dak-Dur 11th Most Wanted
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last tank was 11.26 mpg my truck wasnt blessed with an overhead.
Install one. :p


So was that highway? Because now you've got a problem. Was it including that hour of idling? Because I'd probably get 11MPG if I idled for that long too.

Not throwing any codes or anything?
Did you switch brands of gas lately? If I run 15% ethanol I'll get 12MPG highway straight up.

I'd run some Lucas fuel treatment through it. That always helps to improve my mileage if I haven't run it for a while.

Hopefully it is something minor, or a combination of some minor things.

Wish you luck finding.
 

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Bomb Technician.
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Discussion Starter · #8 ·
my truck is rarely under 45mph, speedlimits around here are 55 i usually go 60. I get my gas from the same place everytime. No check engine lights. truck runs great except for i have a mysterious powersteering leak. im gonna try using some lucas. but 11 mpg just doesnt seem right.
 

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The Anti-RUB
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im not leaking fuel anywhere, id smell that
Not necesarily. I had a fuel leak in my old Explorer and had to crawl under the truck to find it just behind the motor. Couldn't smell it from the engine bay. Turned out to be one of the fuel lines had dry rot and had cracked. It only leaked when the motor was running (when the fuel line was under pressure).
If you haven't done a good smell test, it wouldn't hurt and doesn't take that much time.

btw, I get about 15 MPG on my D' (stock except for mods listed below). Mostly highway driving.
 

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Bomb Technician.
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Discussion Starter · #11 ·
my roommate has a 00 4door dak 4.7 auto 4x4 with 33's and it gets better milage than mine.

Ill have to crawl under it once it dries up. were in the middle of a snow storm right now and i dont like the cold.

btw im running 31x10.50's i noticed that the sticker on the door says my truck calls for 235/75's seems too small of a tire tho.
 
G

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Your speedo is reading over 4 mph SLOW which means you are actually traveling FURTHER than the speedo reads! With the tires you're running, you'll have to ADD 7.266 miles per 100 driven in order to get an accurate reading on you mpg.



Stock Tire - 235/75R15
Tire 1 - 31x10.50R15

Section Width: 9.25 in 235 mm
Section Width: 10.51 in 267 mm

Rim Diameter: 15 in 381 mm
Rim Diameter: 15 in 381 mm

Rim Width Range: 6 - 8.5 in
Rim Width Range: 7 - 9 in

Overall Diameter: 28.87 in 733.29 mm
Overall Diameter: 30.97 in 786.63 mm

Sidewall Height: 6.93 in 176.02 mm
Sidewall Height: 7.98 in 202.69 mm

Radius: 14.43 in 366.52 mm
Radius: 15.48 in 393.19 mm

Circumference: 90.69 in 2303.5 mm
Circumference: 97.29 in 2471.1 mm

Revs per Mile: 720.4
Revs per Mile: 671.6

Actual Speed: 60 mph 100 km/h
Speedometer1: 55.9 mph 93.2 km/h


Speedometer Difference: - Speedometer Difference: 7.266% too slow
Diameter Difference: - Diameter Difference: 6.79%
 

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The Anti-RUB
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Ill have to crawl under it once it dries up. were in the middle of a snow storm right now and i dont like the cold.
When you do, have the engine idling to keep pressure in the fuel lines. Should make it easier to find a leak if there is one. Just avoid any moving parts. :banana2: :worky:

btw im running 31x10.50's i noticed that the sticker on the door says my truck calls for 235/75's seems too small of a tire tho.
265/70R16's is what came stock on my truck. It was the 'wide tire' option. Don't remember what the standard size was.
 

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The Anti-RUB
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Hey bwdakrt, could you post up (or PM me) the full equation etc for those calculations. I don't fallow the spread you made. I understand the difference in diameter/circumference effect actual speed etc, I just don't know how you got the numbers. Thanks...
 

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Bomb Technician.
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Discussion Starter · #15 ·
i bought mine with 31x10.50's on it so i assumed thats what it called for. then i read the door sticker and it says 235/75's and thats just a small tire to me. i had a ranger that ran 235/75's
 

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Bomb Technician.
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339 Posts
Discussion Starter · #16 ·
Your speedo is reading over 4 mph SLOW which means you are actually traveling FURTHER than the speedo reads! With the tires you're running, you'll have to ADD 7.266 miles per 100 driven in order to get an accurate reading on you mpg.



Stock Tire - 235/75R15
Tire 1 - 31x10.50R15

Section Width: 9.25 in 235 mm
Section Width: 10.51 in 267 mm

Rim Diameter: 15 in 381 mm
Rim Diameter: 15 in 381 mm

Rim Width Range: 6 - 8.5 in
Rim Width Range: 7 - 9 in

Overall Diameter: 28.87 in 733.29 mm
Overall Diameter: 30.97 in 786.63 mm

Sidewall Height: 6.93 in 176.02 mm
Sidewall Height: 7.98 in 202.69 mm

Radius: 14.43 in 366.52 mm
Radius: 15.48 in 393.19 mm

Circumference: 90.69 in 2303.5 mm
Circumference: 97.29 in 2471.1 mm

Revs per Mile: 720.4
Revs per Mile: 671.6

Actual Speed: 60 mph 100 km/h
Speedometer1: 55.9 mph 93.2 km/h


Speedometer Difference: - Speedometer Difference: 7.266% too slow
Diameter Difference: - Diameter Difference: 6.79%
not trying to burst ur bubble and im not arguing your math but my speedo is definatly not off. its dead on according to gps and radar. so either its been recalibrated or gps and radar lie
 

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Dak-Dur 11th Most Wanted
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my roommate has a 00 4door dak 4.7 auto 4x4 with 33's and it gets better milage than mine.

btw im running 31x10.50's i noticed that the sticker on the door says my truck calls for 235/75's seems too small of a tire tho.

Many Daks came with 31X10.50s (same as 265/70) My old Sport did, and my new Quad Cab did too. Like you say, it is dead on with GPS. I don't know what the door sticker is about, but some of the others came with 235/75s. My Durango has 235s and both my Daks have had 31s. So I'm sure you are correct, they came stock on your Dak.

However, here's my question. Is your roommate's speedometer re-calibrated for the 33s? That would throw off his mileage and his numbers are worthless.

But you never answered my questions from before. Did you let it idle for an hour and then get 11MPG on that tank? Did you switch brands of gas? Use ethanol? You said you don't like the cold, how long do you let it idle in the morning? These things are HOGS when idling. You know this of course, but it is worth pointing out that while you are idling in the parking lot, you are getting 0 MPG. When you go to average things and have a bunch of 0's thrown in, the number drops in a hurry (I know, I'm a teacher....lol).
 

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Bomb Technician.
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Discussion Starter · #19 ·
i know ideling is bad for mileage. most days i just jump in and go after all the guages go to their proper places. i still avg 10-13.
 

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It's very possibe the speedo could've been recalibrated to match your tire size. I know it takes almost NO time to do at a dealership, and most I worked for would even do it for nothing (even the service writers were capable of using the scan tools). I honestly can't say what could be the cause. I have 255/60R17 on R/T wheels on my 4.7Quad. I never let it idle to warm up. I just get in, start, and go even in winter weather. My last tank averaged 13.3mpg with some very cold days and lots of quick take-offs, so I couldn't imagine how you could be getting poor mileage short of excessive idling. I do, however, maintain my tires at 50psi and get even wear. I thought this was bad, as I get as high as 17-18mpg during the summer, but I remembered the colder weather results in longer warm-ups, and snow/ice have created a LOT of slippage even without heavy throttle.
 
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