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-   -   fuel mileage - first calculation (http://www.ramforumz.com/showthread.php?t=63059)

nanney1 10-06-2010 08:15 AM

fuel mileage - first calculation
 
06 Quad, 4.7, 2WD, 3.55. Everything stock except tires. Factory spec was 245 70R17 and when I bought it the previous owner had switched to a P265 70R 17. Not much difference but the tires are noticeably taller than the 245's I've seen.

1. O.K. first full tank fill up. At the end of the run, the overhead computer notes 16.0 mpg for the full tank run.

Distance driven was 368.5 miles and it took 24.911 gallons to fill back up. So, my hand calculation says 14.79 mpg.

So, what gives? Is the computer slightly off due to the size of the tires? Or is a 1.2 mpg differential normal from what people see listed on the computer in comparison to hand calculations?

2. Any thing I can do very cheaply to help with fuel mileage? I already drive slowly and stay under 2000 rpms all the time. Curious as to what putting my foot into it a little more would do. Off the top of my head, changing the air filter, and adding air pressure to the tires are two simple and cheap things I can try.

erm 10-06-2010 08:20 AM

The computer is an adaptive device and mileage computed seems to be sensitive to the slightest change to speed, throttle input %, etc.

I don't rely on mine...I've seen it change within 2 minutes of starting to pull a hill. I go with the old fashioned way of manual calculating. It's an accurate method of total mileage measurement.

You can add an intake to the engine to help it get a bit more air and run a bit cooler. That will make for a more efficient engine. You might also want to consider adding a freer flowing exhaust to promote exhaust scavenging, another way to help with engine efficiency.

One thing to keep in mind. Keeping below 2,000 RPM all the time, especially around town, might be lugging the engine a bit and it won't efficiently use the fuel. For steady state cruising, that's a good practice. For around town, bump it up a bit, drive in a bit lower gear or with O/D off. It will help.

07QUADCABTN 10-06-2010 03:50 PM

Quote:

Originally Posted by nanney1 (Post 327844)
06 Quad, 4.7, 2WD, 3.55. Everything stock except tires. Factory spec was 245 70R17 and when I bought it the previous owner had switched to a P265 70R 17. Not much difference but the tires are noticeably taller than the 245's I've seen.

1. O.K. first full tank fill up. At the end of the run, the overhead computer notes 16.0 mpg for the full tank run.

Distance driven was 368.5 miles and it took 24.911 gallons to fill back up. So, my hand calculation says 14.79 mpg.

So, what gives? Is the computer slightly off due to the size of the tires? Or is a 1.2 mpg differential normal from what people see listed on the computer in comparison to hand calculations?

2. Any thing I can do very cheaply to help with fuel mileage? I already drive slowly and stay under 2000 rpms all the time. Curious as to what putting my foot into it a little more would do. Off the top of my head, changing the air filter, and adding air pressure to the tires are two simple and cheap things I can try.

I have a 07 4.7 quad 2 wheel drive. It gets around 15.5 around town and about 16.7 on the highway. A little better if I don't use cruise. The truck is heavy and the motor is weak. Mpg isn't going to get much better. If it is a flex fuel truck don't use E85 ran 327 miles on the highway no stops the other day 14.46 mpg . 1st and last time I do that.

nanney1 10-06-2010 03:57 PM

I don't think mine is a flex fuel. Here's what it notes on the build codes for my 4.7:

EVA 4.7L V8 MPI Engine


So, don't use cruise control? Why not?

RootBeer 10-06-2010 04:39 PM

Using the on-board computer is iffy at best. To many variables. Manual calculation for mpg is the only way to know for sure.

Adding a CAI and good exhaust will garner you the most.

As for cruise, its great on the hiway. Never use it around town. The only downfall to the cruise control is that when going downhill is it will downshift rather than coast. Consequently it doesn't take advantage of the few seconds of added mpg you would get from coasting.

BigOrange 10-06-2010 08:00 PM

I've got an '08 4.7L w/ intake, Y-pipe, Dual Exhaust, & synthetic oil. I keep the tires at 35lbs., & usually get about 14.8 mpg with a mix of city/hwy driving & easy/aggressive accelerating. (I like to hear and feel my mods at work!!!) The 14.8 is hand calculated, the computer always shows about 2-3 mpg more.

07QUADCABTN 10-07-2010 09:34 AM

Quote:

Originally Posted by nanney1 (Post 328098)
I don't think mine is a flex fuel. Here's what it notes on the build codes for my 4.7:

EVA 4.7L V8 MPI Engine


So, don't use cruise control? Why not?


Well I realized that with the 3.55's the throttle would bury to the floor while on cruise. Instead of kicking down into 4th or out of lock up. If I run it off cruise I can get it to kick down easier. I traded a 05 Durango SLT with the same motor and trans and it worked awesome with cruise seeing 21 to 23 on the hwy. I guessing the truck is a little heavier. I would like to here if anyone has used a programmer to get better economy. I only traded for the tow capacity with my newly acquired camper. The truck pulls it much better.

05atlanticblue 10-07-2010 06:02 PM

the computer nothing more than a glorified vacuum gauge

moparmanicac 10-08-2010 12:45 AM

Ive hand computed mine for two different weeks before and after my exhaust and both times the computer was within .35 of a mpg I have r/c 4x4 4.7 w/ the 3.92s with just an exhaust so far and pull about 13 around town 16-18 highway I usually avg. about 14-14.5 Im thinking the taller tires would throw the mpg outta whack to on the computer

nanney1 10-08-2010 08:42 AM

I've started driving with Overdrive off except on the highway above 55 mph. Noticeable differance in the feel of the truck. Higher RPM's and a better feel. Not lugging like I was previously driving 35-45 mph with O/D on and RPM's down around 1500. The computer MPG average doesn't seem to drop as much despite the higher RPM's.

Also, I quit using cruise control on the highway runs to take advantage of coasting. We'll see on the next fill-up.


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