ok I figured you didnt have the calculator...(and mentioned that) I have the same year truck as you...
3.92 was stock for stock size tires that came on your truck... when you changed your tire size from factory size it throws actually speed and distance off because the pcm has no way of knowing that... your speedo and odometer are in fact off unless they were reprogrammed for your specific tire size... if you were to put 4.56 gears in your truck the speedo and odometer would be more accurate without reprogramming since it changed the drive trains final gear ratio back to what it was stock.
One tire revolution on a bigger tire (more surface area) will move you farther than the same revolution on a smaller wheel... this effects the speedo and odometer. The spedometer and odometer are programed for the distance moved on one rotation of the factory tire size... so all those calculation you made would be off even though you would have done them the right way if your gauges were dead on.

 

Give it up please I now what I am up to. Maybe you should have asked if I have changed the speedo gear. I have been a mech of a very long time +20 years so i am no desk jockey.

 

Give what up I'm just trying to keep the facts straight? Your mpg isnt avaerage for your setup and I'm trying to clarify why it might be off... The 96 doesnt have that gear for speedo calculating I was told although I guess I was misinformed... Just 98 up? I did ask if that gear was changed in my original post and then removed it when I saw you have a 96.
In any case you should have mentioned that if you did it...would have made things a lot less confusing for others...

 

I suppled figures pertaining to the org post, you decided to confuse things. My mpg is spot on has been for years.

link for speedo gear replacement part.

http://www.go.jeep-xj.info/HowtoSpeedoGears.htm

 

yeah I saw that.... I got the years backwards...98 up can have the pcm reprogrammed 94 -97 can have the gear in the tranny changed... you mentioned the speedo being right on because you had factory 3.92 gears which would be wrong in itself with bigger tires and has nothing to do with the gear in the transmission you never mentioned replacing.... ok it makes sense now... wow I'm impressed you get such good mileage.. most 5.9's cant touch that with stock tire let alone 315's guess being a mechanic and staying on top of things has its perks in this case.. Its still good this was all mentioned for others that dont know how the tire size effects things..
BTW you just hit 1,000 posts...your a record breaker now.

 

I'd be interested in how this is done myself. I consider myself a good mechanic and have owned my truck pretty much (bought 2001) since new . I have taken care of plenum issues and all the mechanical maladies that plague the 5.9. It has been deathflashed.
Best mileage is 13 hwy. That's on flat interstate and with a tailwind.

 

35's on stock 3.55's... made me spend some cash on a new transmission. i have never seen a transmission go boom so quickly....

 

Thanks and you are spot on keeping up on you trucks maintenance pay's off, most would think I am nuts for my tune up schedule and what parts are replaced in those tune ups. I have thousands invested into my motor in parts, if I had not built this motor I would indeed be lower on gas mpg. Will I ever see my money back in gas mpg nope never. I would like to see what I would get for mpg on the flat lands as all of my driving is in the mountains.

Edit: My biggest mpg gain is from the Mopar performance pcm. Also I should say that i have deleted my a/c comp and that helped some as well. I average 10hrs a week going over my truck to make sure its all working as it should.

I should also add that mpg is with 25.7lbs injectors instead of the 24lbs injectors.

Op sorry for being off topic.

 

Holy crap cutthroat...how many fricken threads are you going to start always talking about tires/wheel size?!?! Use the damn search function!



AuggieDoggie - You are by no means the benchmark for everyone in terms of tires and gears and tranny and mpg. The ONLY topic I personally give you credit is on HID lights. I'm tired of you being so abruptly dismissive about people's offerings and their experience. You doubt every single thing. Again, stop attempting to be the benchmark for everyone. Lastly, when you actually do some engine mods...nvm I'm done ranting.

 

27...I use the search function but I wanted only peoples opinions who have done this that's why I started this thread.But don't worry all of my questions have been answerd.So Im done asking