****** computer re flash?

hadtomer · Jun 3, 2018

Hello-

Fitted larger tires today and met a fellow libby owner at the tire shop.

Much t my surprise he told me about some sort of ****** computer re flash that can take into account larger tires, change the shift pattern and such.

did anyone here hear about something like that?

LibertyTC · Jun 3, 2018

It's actually a calibration done by any dealer that knows what they are doing w/ a Star Scan.
What size tires did you install?
From post 19-

tjkj2002 said:
Having your speedo calibrated for larger tires is not only to correct the speedo reading,it greatly effects how the auto trans shifts.If the speedo is programmed for smaller tires(even if speedo is off by 5% which is normal) and you have larger tires,by at least 1" or more in total diameter then stock, it will confuse the trans and make it shift wrong which makes you mad and give it more gas to kick down which makes it shift more which creates more heat which more heat causes early trans failure.

Link to above thread^: http://www.jeepkj.com/forum/f200/tire-size-change-39894/

rjkj2005 · Jun 4, 2018

I've been running 265/75/16 with factory 3.73's for a while with the factory transmission settings. No issues except that the speedometer is off. As far as shift point changing. Why. With the larger tires you need to stay in gear longer. Right now it up shifts still at the factory settings of 45 mph. Which means I'm going almost 50mph. Now when I'm in a 45 zone I'm showing 40 mph on the speedometer and in the correct 3rd gear. Which is a better rpm than 4th with the larger tires. If I recalibrate that would mean that it will still up shift at 45 mph which would be the actual speed with the larger tires. Then the transmission would start to yo-yo between gears till I got to 50 mph +
Plus the 5 dealers I've talked to will only increase tire size in the PCM to 245/70/16s. The largest tire size jeep says will go on a factory hight KJ. At least around my area.

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hadtomer · Jun 4, 2018

I am running 4.10 gears so i guess it does not really matter. i was running 245/75R16 and I took a set of 235/85R16 for a spin. I don't think they will require 4.56 gears- just a bit of fettling.

tommudd · Jun 4, 2018

rjkj2005 said:
I've been running 265/75/16 with factory 3.73's for a while with the factory transmission settings. No issues except that the speedometer is off. As far as shift point changing. Why. With the larger tires you need to stay in gear longer. Right now it up shifts still at the factory settings of 45 mph. Which means I'm going almost 50mph. Now when I'm in a 45 zone I'm showing 40 mph on the speedometer and in the correct 3rd gear. Which is a better rpm than 4th with the larger tires. If I recalibrate that would mean that it will still up shift at 45 mph which would be the actual speed with the larger tires. Then the transmission would start to yo-yo between gears till I got to 50 mph +
Plus the 5 dealers I've talked to will only increase tire size in the PCM to 245/70/16s. The largest tire size jeep says will go on a factory hight KJ. At least around my area.

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They can do more, Jeep dealers have done 5 for me to 265-75-16s

tommudd · Jun 4, 2018

hadtomer said:
I am running 4.10 gears so i guess it does not really matter. i was running 245/75R16 and I took a set of 235/85R16 for a spin. I don't think they will require 4.56 gears- just a bit of fettling.

Does matter and makes a difference
You must live in a flat area I always wanted 4.56s with my 32s
the 265-70-16s on my DD are perfect with 4.10s

tommudd · Jun 4, 2018

LibertyTC said:
It's actually a calibration done by any dealer that knows what they are doing w/ a Star Scan.
What size tires did you install?
From post 19-

Link to above thread^: http://www.jeepkj.com/forum/f200/tire-size-change-39894/

This and regearing,....people will argue for hours that it is not needed, that is until they ride in one that has had the reclaibration and regearing done

rjkj2005 · Jun 4, 2018

tommudd said:
They can do more, Jeep dealers have done 5 for me to 265-75-16s

Yes I know. Just the dealerships around me won't do it for more.

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rjkj2005 · Jun 4, 2018

tommudd said:
This and regearing,....people will argue for hours that it is not needed, that is until they ride in one that has had the reclaibration and regearing done

Does regearing make a difference. Sure. There's no doubt it would make a difference. But is it "needed"? Is it necessary? No. Would I do it if I had the extra cash. Probably not. I spend 90% of my time in town. OD off up to 55. It works fine for my area.

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wheeee32 · Jun 6, 2018

How much do they typically charge for the transmission re-flash?

nbas · Jun 7, 2018

How much do they typically charge for the transmission re-flash?

I went to the Dealership, explained what I wanted to do to the mechanic. They did not know what to charge at first and finally I paid something like 10-15Euro's...
I see in your signature that you have re-geared (in Greece since I see a Greek name?). Where did you do it (if in Greece) and how much it cost? Any issues since?

04Liberty · Jun 7, 2018

All it is, is changing the pinion factor in the computer.

****** computer re flash?

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