GreenS550
Well-Known Member
- Joined
- Nov 18, 2017
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- 126
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- Location
- Houghton, MI 49931 Oakland, MI 48363
- First Name
- Bob
- Vehicle(s)
- 2019 Mustang GT Premium 2020 Explorer Limited
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- #1
I wanted to share what I learned about getting the stock tune to have the car operate properly after an axle change. Some of this might be already known, but it saved me when I traded my 2016 Mustang GT M6 in today.
I bought a 2016 Mustang GT M6 in perfect condition last year. My goal was to enjoy the car through the winter with A/S tires and learn how to change the differential along with the tune in preparation for the upcoming Mach I I was planning on ordering. The car ran absolutely excellent stock, but after swapping differentials from 3.31 to 3.55, the car would not really accelerate past 4K rpms in 3rd and 4th. Having exhausted my very limited knowledge about how to address this, I finally broke down and ordered a tune from American Muscle (Bama) to correct the problem.
Wow. It was an excellent tune and the car ran impressively good. But, it still didn't solve the main problem of how to fix the issue when reverting back to stock. Several folks on Mustang6g believe the car will run fine with out a change in the computer. This is simply incorrect. The speedometer will read correctly, but the sensor in the tailshaft of the transmission and the speed sensors at the wheel will not agree, hence the "limp mode".
Then we were told to just change the code in Forscan to the correct gear ratio and all is well. Wrong. It will not work because the axle ratio is in the PCM as well as the BCM. Changing the BCM code will not fix it. So, what to do? Here is a work around that I read about from I believe another Mustang6G member.
What you do is change the TIRE SIZE code to equal the gear change. Then another guy did an excellent job at creating a file that you copy and run with the changed tire sizes. Here is what I did:
My car had 255/40R19 tires. I looked up this tire on Tire Rack. It produces 770 revs per mile. Then I took the gear changes made: 3.31 to 3.55 and determined the percentage change. To do this you divide 331/355, which gives .93. Multiply .93 x 770 which gives 716 revs per mile. Now, you have to look at several tires on Tire Rack that are close to this number. I found 295/35ZR21 tires had 715 revs. Close enough.
So, now you have the tire size. From there I found this:
Which you copy the file and put in the tire size, in this case, 295/35-19, which gives a value of 08C8 for the Hex value. Once I did this the car ran perfect. No codes, nothing. Just ran excellent.
The line is 726-12-01 XXXX 08c8 XXXX. Note that you do not change the first four digits, in my case from 014B TO 0163. No, leave this alone, it does nothing.
The real help here is the person or persons that designed the calculator that I have referenced above. The possible tire sizes are immense and I am thinking when I get the M1 I will be able to fix it as simply as this.
Hope this helps!
I bought a 2016 Mustang GT M6 in perfect condition last year. My goal was to enjoy the car through the winter with A/S tires and learn how to change the differential along with the tune in preparation for the upcoming Mach I I was planning on ordering. The car ran absolutely excellent stock, but after swapping differentials from 3.31 to 3.55, the car would not really accelerate past 4K rpms in 3rd and 4th. Having exhausted my very limited knowledge about how to address this, I finally broke down and ordered a tune from American Muscle (Bama) to correct the problem.
Wow. It was an excellent tune and the car ran impressively good. But, it still didn't solve the main problem of how to fix the issue when reverting back to stock. Several folks on Mustang6g believe the car will run fine with out a change in the computer. This is simply incorrect. The speedometer will read correctly, but the sensor in the tailshaft of the transmission and the speed sensors at the wheel will not agree, hence the "limp mode".
Then we were told to just change the code in Forscan to the correct gear ratio and all is well. Wrong. It will not work because the axle ratio is in the PCM as well as the BCM. Changing the BCM code will not fix it. So, what to do? Here is a work around that I read about from I believe another Mustang6G member.
What you do is change the TIRE SIZE code to equal the gear change. Then another guy did an excellent job at creating a file that you copy and run with the changed tire sizes. Here is what I did:
My car had 255/40R19 tires. I looked up this tire on Tire Rack. It produces 770 revs per mile. Then I took the gear changes made: 3.31 to 3.55 and determined the percentage change. To do this you divide 331/355, which gives .93. Multiply .93 x 770 which gives 716 revs per mile. Now, you have to look at several tires on Tire Rack that are close to this number. I found 295/35ZR21 tires had 715 revs. Close enough.
So, now you have the tire size. From there I found this:
Which you copy the file and put in the tire size, in this case, 295/35-19, which gives a value of 08C8 for the Hex value. Once I did this the car ran perfect. No codes, nothing. Just ran excellent.
The line is 726-12-01 XXXX 08c8 XXXX. Note that you do not change the first four digits, in my case from 014B TO 0163. No, leave this alone, it does nothing.
The real help here is the person or persons that designed the calculator that I have referenced above. The possible tire sizes are immense and I am thinking when I get the M1 I will be able to fix it as simply as this.
Hope this helps!
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