Engine/Transmission (1998.5 - 2002) poor fuel mileage

[mfurrh55]

The 01 used to have was running 72 mph at 2100 rpm ,and was pretty good at 20-21 mpg. ,5 speed dually,Had it for 7 yrs. i did have a Banks kit on it though, Monte

 

[bry1216]

Just caught this thread. Your mileage is exactly what it should be. My '01 3500 4x4 would get around 14. 5-15 in the winter months and 17-ish in the summer months for every year of the 12 that I owned it. Really not much different depending on my mods, either (stock to 450hp and back to 300-ish). Old or new MAP or IAT. So don't spend too much time or money trying to look for extra mpg.

Any engine mods will throw off the overhead MPG meter. The computer calculates the fuel flow based on a stock tune - there is no actual measuring of the fuel flow. So if you put in injectors that flow more fuel than stock with less effort from the injector pump, then the computer only sees the less effort and thinks it is getting better mileage. Put on a box or a programmer and you'll have the same thing. I think mine averaged in the low 20s for most of its life.

My 1999 24v auto has 3. 55 ratio and 245/75/16 tires. Using a Garmin GPS recently I travel 340 miles out and back on an average mountain paved 2 lane highway in Idaho and Montana. Filled up until I could see the fuel before leaving and before returning - 18. 5mpg. Computer stated 21. 5mpg and odometer 388 miles.
Engine and transmission are stock. Been this way for 95,000 miles.
My calculations show the circumferences inches:
LT245/75/16 = 95. 7 (9. 65 inches wide) 1999 Stock Steel Rims
LT265/75/16 = 99. 4 (10. 43 inches wide) 1999 Stock Mag Rims
LT235/85/16 = 99. 6 (9. 25 inches wide)

I have to ask, "why add injector cleaner to your fuel?"

Hope the info helps.

 

[VolsFan]

bry1216, that sounds like good fuel mileage for a 99 auto. I fueled up today and got 15. 8 mpg. I am running 235/85/16. That mpg number is w/ the new 40 hp bosch injectors and nothing else. Its better than what I had been getting in the truck. As for running cleaner, I have always been concerned about the diaphragm in the injection pump cracking w/ the lack of lubricity in the new fuel. I could be totally wrong and just throwing money away, but havent lost an injection pump. Also, I think the 4. 10 is killing my mileage more than anything, but it is great for towing. I am happy w/ the power the truck puts out, but once I get done w/ moving and settle down again, think Im going to get a smarty for a little extra oomph and possible better mpgs

 

[Sticks]

Right foot, rolling resistance (tread type ~ aggressive mud/snow vs. plain Jane street), aerodynamics and weight are the 4 big factors in MPG.

I am still trying to figure out why I get 14-15 city, 15-16 highway (65-75mph), and 20-22 in the mountains (55-65mph). I know the bumper mounted brush guard killed city/highway mileage by 3mpg (that showed up right away). Mileage has been the same from stock engine to current config.

 

[PC12Driver]

I am still trying to figure out why I get 14-15 city, 15-16 highway (65-75mph), and 20-22 in the mountains (55-65mph).

Whatcha trying to figure out about that? Sounds right in line with what you should be getting.

My best tank was in the mountains, too. Right about 22mpg at 45-50mph. I thought my fuel gauge was stuck.

 

[Sticks]

Whatcha trying to figure out about that? Sounds right in line with what you should be getting.

My best tank was in the mountains, too. Right about 22mpg at 45-50mph. I thought my fuel gauge was stuck.

It's just the logic dictates that you should be using more fuel climbing 6% and 7% grades for miles at a time than you would be saving on the downhill run, let alone the Edge and lack of air at 8k - 10k in altitude.

... Oh yeah, it's a Dodge. It's not stuck (fuel gauge) just really inaccurate. Quarter tank means start looking for fuel real quick cause you are on your last couple gallons.

 

[PC12Driver]

Newton says that if I ended up at the same elevation that I started (home), then the net energy usage for hills would be zero. I figured the good mileage in the mountains was more to do with the relatively lower speeds and the decreased air density, since aerodynamic drag is the primary factor in fuel economy on the highway.