Changed out tires to 275/70...mpg, speedo, timing is off... - Page 2 - JeepForum.com
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post #16 of 24 Old 05-04-2011, 07:12 AM
jstrubberg
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Quote:
Originally Posted by Coilrod View Post
Neg. Call tech support for your programmer. The jk calculates it's own gear ratio. Don't take my word for it. Tire size and speed sensors.
I spoke to both hypertech and diablo. Call them.


Then something on my 09 is broken. I bought it with 6k miles on it and 5.13s installed....it ran like utter crap until I reset the ratio.

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post #17 of 24 Old 05-04-2011, 07:41 AM Thread Starter
diveguy
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Just to re-cap...and I have an auto tranny...

ProCal is a programmer that I will be able to reset the computer so it reflects the correct speedo, thereby correcting the CALCULATION of MPG, not physically adjusting the MPG (be it more or less).

This is where I get confused...I am reading the previous posts as this: The computer is set to a gear ratio that my Jeep came with stock (3.73) and the programmer can adjust the gear ratio (or rather the "appearance" of gear ratio adjustment) to improve MPG...in other words, even though I physically have 3.73 gearing, I can make the computer "think" that I have 4.10 or 5.13...which will adjust the gear change timing. Is this right? That seems crazy easy to me... If this is the case, I would need a Flashpaq, NOT a ProCal...?

If I am completely off-base, sorry bout that...the JK and TJ are two different beasts so I need to adjust how I think the JK works when compared to the TJ...

In any case, can someone tell me what would be the most cost-effective way to:
1) Increase MPG (not by .5 miles but by like 4-8 miles per gallon)
2) Adjust my gear timing so I'm not in 1st until 2500 RPM...exaggeration but you know what I mean...
3) Correct my speedo to compensate for my larger tires
4) Increase overall performance

Thanks for all the input!! Learning alot about this baby from all of you...much appreciated!

2008 Blue Sahara Unlimited
275/70R18 (33.2 x 10.5) BFG AT/KO
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post #18 of 24 Old 05-04-2011, 07:48 AM
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Nope. In my case, the Jeep had been re-geared to 5.13. The tuner didn't allow me to fool the Jeep into making more gas mileage...it corrected an error that got me gas mileage back that had been lost by a tranny that was shifting in the wrong spots and dogging the engine all the time.

1. You can't. That kind of increase isn't going to happen on the Jeep platform. Again, the only way to get stock mpg is to run stock tires, stock ride height and stock weight.

2. Any tuner can take care of this for you.

3. Again, any of the name brand tuners will do this.

4. A tuner will probably increase performance slightly. If you are looking for a major increase, save your pennies for a Hemi or better gearing.
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post #19 of 24 Old 05-04-2011, 10:36 AM
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I'm not a rocket scientist... but the "appearance" of improved MPG's only happened because the speedo was finally calibrated for the appropriate tire size. I can say that when I put my 35's on, and drove it for a bit before I recalibrated... by using a GPS app on my Android, when I thought I was going 65, I was actually going about 74 miles an hour. Thus, the Jeep thinks I'm going slower than I actually am, but buring more fuel, therefore, the computer calculate I was getting 11mpg on the highway. The next day, I recalibrated (took a few tries because my measurement wasn't correct, and I used the GPS app to finally get it spot on), I now average 13 to 14, which is fair, considering I was getting 16 to 18 before.

Regarding gearing... unless the computer is monitoring driveshaft spin speed in relation to the wheel sensors, I don't see how it would know what gear ratios are installed. But then again, I'm still learning about this computerized JK after coming from my TJ, where we just replaced the speedo gear in the tail housing to best match our setup.

-Ken
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post #20 of 24 Old 05-04-2011, 10:59 AM
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Quote:
Originally Posted by aznjeep View Post
I'm not a rocket scientist... but the "appearance" of improved MPG's only happened because the speedo was finally calibrated for the appropriate tire size.
@ jstrubberg-Was the odometer previously calibrated before the gears were changed?
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post #21 of 24 Old 05-04-2011, 11:20 AM
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I hadn't changed my gears yet. I've got to save up $1k more before I can do that. I've only got $400 put away at this time for gears. I was chiming in for the previous posts... The AEV ProCal doesn't improve MPG's, it only allows us to enter in parameters into the computer so that it can do all the calculations to reflect near accurate information. That, and I was trying to understand how the wheel sensors tells the computer what gear ratio is installed without also monitoring driveshaft spin speed. If it DID monitor DS spin speed, then yes, the computer would be able to figure out gear ratios. But to my knowledge (at this time), the JK's don't monitor DS spin speed (rotations). I guess I'm trying to figure out where Hypertech and Diablo came up with that response...

-Ken
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post #22 of 24 Old 05-04-2011, 12:00 PM
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@aznjeep- I was referencing your post and asking jstrubberg the order in which he did the upgrades and changed the gear setting in the computer.


Call the guys at AEV and talk to them about the Procal. They know the JK very well. Don't let all the internet BS misguide you.
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post #23 of 24 Old 03-16-2019, 05:37 PM
i3ig Gun
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Im actually having this same issue with my 2013 jk, I own the flashcal from superchips, and was able to change my tire size... but im afraid to change my ratios. I have stock drivetrain and im afraid of i adjust the computer that I'll break something mechanically... any advice?
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post #24 of 24 Old 03-16-2019, 05:44 PM
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I3ig Gun

Quote:
Originally Posted by jstrubberg View Post
The Procal does the job just fine. I did see an increase in mpg when I corrected the gear ratio, but you won't get stock mpg. The only way to do that is to run stock height, stock tires and stock weight.

I went from 13.5 mpg to 16 mpg by resetting my gear ratio from the stock 3.73 to the correct 5.13.

And btw, a supercharger will LOWER mpg, not raise it. Sorry.
Did you physically change the ratios with new equipment, or just tell the computer to move from 3.73 to 5.13

because I'm terrified I'm going to break something if I do that... my 2013 JK is shifting way to high and dogs out going up slight inclines..
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