Can I use a Flashcal to reset the computer to OEM specs and the wheel size that is on the Jeep now?

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Shotgunr

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Rock and Cows, Minnesota
New to the forum and new to Jeeps! Always wanted to own one and happy as heck to be here! So I purchased a 2017 JK with some minimal right rear body damage (No fender, inner liner or bumper and taillight). However, I was told that the axle was replaced after this accident. On the drive home I have an engine light, and I appear to be in limp mode. The code for the light is P0731 (Gear 1 incorrect radio). The auto stick will not shift higher than 2nd gear. RMP's on the road are 3500 at 60 MPH. The spare is in the back is a Mickey Thompson 285/70R18. I'm unsure what the gear ratio is for the axle but was told it was replaced with an OEM 2017 wrangler axle...so I assume 3:21. The previous owner must have taken the tires, left the spare and then installed OEM wheels and wrangler OEM tires that are 255/70/R17. Checked the speedo with GPS and its off about 1.5 mph.

Question is this: Can I use a Flashcal to reset the computer to OEM specs and the wheel size that is on the jeep now? I would assume that the larger tires where reset in the computer and not set back to OEM after the previous owner took those larger tires off.

Again, thanks for having me and any advice would be very appreciated!
 
Not sure about the Flashcal but my guess the issue is probably the speedometer being off. If it was my JK i'd be pulling the front and rear diff covers and making sure that both have the same ratio gears in them. Then it would be also nice to know what ratio they are if both are the same. Most of the years of JK's had 3 different gear ratios available so I wouldn't assume they are the same.
 
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1. Definitely need to determine what gears you're running. And, like Black mentioned above, please make sure the front and rear gears are alike.
2. Program the correct gear ratio.
3. Program the correct tire size.

Step 1 is critical, because if the previous owner changed the rear gearing and left the front alone because he'd never use 4WD, you'll probably blow up the transfer case the first time you put it in 4WD and put it in gear. That repair alone could run you $2k.
Please do not assume what is on the rear differential is what the current gearing is. You already know it's not right. Again, like Black said above, you have little choice but to pull the covers and see for yourself what gears your Jeep is running. Trusting anything less that your own eyes could be expensive.
 
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Anybodyhome said:
, you have little choice but to pull the covers and see for yourself what gears your Jeep is running. Trusting anything less that your own eyes could be expensive.
Click to expand...
You don't need to pull the covers, I checked the ratio by jacking up the wheels, putting it in neutral and rotating the back tire. (the other rear tire needs to be held still) when doing that count the rotations of the drive shaft. that is your gear ratio. You can then do the same for the front.
As stated above, it is super important that front and back are the same.

The vid here shows how, though he doesn't mention that you need to hold the opposite tire in place. Or I guess you could just rotate the one tire twice.
 
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Just my opinion since it's a new vehicle for him it would be good to look inside to make sure everything looked good and not full of water. Never know what the rear axle came out of and what it was used for in the original. That way start from scratch with clean oil and know your good.
 
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BLACKJKU said:
Just my opinion since it's a new vehicle for him it would be good to look inside to make sure everything looked good and not full of water. Never know what the rear axle came out of and what it was used for in the original. That way start from scratch with clean oil and know your good.
Click to expand...
Fair enough. I suppose especially considering where the axle came from. For me taking the cover off would tell me nothing beyond making a mess. Do you count the teeth?
 
MacGuyver said:
Fair enough. I suppose especially considering where the axle came from. For me taking the cover off would tell me nothing beyond making a mess. Do you count the teeth?
Click to expand...


On the edge of the ring gear is a part number, date, and teeth count stamped there. For example if it has 4.10 gears it would have 41-10, 41 teeth on ring gear and 10 teeth on the pinion.
 
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It's always good to have first hand look to see just what you have and take pics to log for later
 
MacGuyver said:
You don't need to pull the covers, I checked the ratio by jacking up the wheels, putting it in neutral and rotating the back tire. (the other rear tire needs to be held still) when doing that count the rotations of the drive shaft. that is your gear ratio. You can then do the same for the front.
As stated above, it is super important that front and back are the same.
Click to expand...
This is a chart I've shared in the past:
1608296765557.png


I only suggested pulling the covers because the owner said "he was told the axle had been replaced." Nothing screams "take it apart and look for yourself" more than this. Too many unknowns to trust your drivetrain to, in my opinion.
 
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