UPDATE Limp mode after differential change. Need advice

[GreenS550]

Hello all.
I just finished up on the diff change from 331 to 355 on a manual transmission 2016 Mustang GT. The install went great, but the car doesn't want to really accelerate. Running smooth but no power at all. The speedometer is correct as I checked it with my GPS.
Clearly the computer is limiting gas, etc. It feels like it has no gas after about 3500 RPM and even getting there much slower than before
I have a 93 canned SCT tune on the car. The axle ratio is not an adjustable option on the tuner.
Any ideas?

Sponsored

 

[ice445]

You can change the axle ratio in the BCM with ForScan.

 

[GreenS550]

I have never used forscan. But, willing to give it a shot! Any suggestions on getting started?

 

[NoVaGT]

Call your tuner, and let them know what is happening. If they're reputable, they should take care of it for you.

 

[GreenS550]

I checked a bunch of videos, etc and got the Forscan license and will get the device tomorrow.
Looking forward to checking it out and seeing if this fixes the issues.
Any other tips are appreciated.

 

[jimmerheck]

I have read many times on here from many members that the M6 cars dont need any kind of a software change when the rear gear ratio was changed. Because I am considering the same, so have done a lot of reading on it. Are you absolutely sure something else didnt happen while changing the rear end?

 

[Sweetface]

I was told by my tuner I needed to update my tune when changing my gears. Installer test drove the car before update was loaded and got a CEL turned back around . I got there shortly after loaded updated tune and no issues at all . I'm not sure of the specifics but it's more than just a speed correction update.

 

[GreenS550]

Absolutely sure nothing else was changed. No plugs unplugged, nothing. The only modification it had was an SCT tune and I flashed it back to stock. But I have since read a number of cars that have had exactly the issue I'm going through. I'm just wondering if it matters whether you have a base Mustang or premium yes I thought there were different drive modes and perhaps that has something to do with it. The traction control light will go on when the tires are spinning and it's very weird because I took it out today and a couple times in fourth it was as though it had full power and then it would just shut down. I'm going to figure out how to use the foreskin but I also ordered a tune with a 355 gearing as part of the tune. I spoke with American muscle this morning and they told me they can adjust the computer up to a pretty low gear ratio like 480 or something. Including rev matching on the 18s and up. But I don't have any way to confirm that.

my purpose in the 16 is to try different things before I go ahead and bite the bullet on a Mach 1. Because I know the Mach 1 is likely going to have the same gearing as my bullet did which was crappy. I will update this when I know more. But apparently the ABS sensor that determines the speedometer has to interface with the other parts of the BCM. So it makes sense I'm having problems because if the car is spending the drive shaft faster it's not going to be able to make sense with the 331 gearing that's in the computer.

 

[GreenS550]

Sorry about that error. I already know how to use the foreskin I mean I have to learn how to use the four scan

 

[Sweetface]

If you seem to run into any road blocks. Send an email to a reputable tuner ( only have experience with PBD ). I switched to a 4.09 and their updated tune and personally is the mod I've enjoyed the most.

 

[vanquishvzla]

kam reset?

 

[BMAGOO]

When the dealership changed my 3.31 to 3.73 I had the same issue. The dealer had it for about a week before they figured out the problem & fixed it. Unfortunately I don’t know what they did to fix it. Could’ve been Forscan.

 

[jimmerheck]

This might not help you, but a member on here, K4fxd claims to differ about changing any bcm values or such after a rear end swap on a 16. Maybe the 18's on up need it, but he claims, not needed on a 2016 which is what you have. Maybe DM or PM him?

 

[ice445]

This might not help you, but a member on here, K4fxd claims to differ about changing any bcm values or such after a rear end swap on a 16. Maybe the 18's on up need it, but he claims, not needed on a 2016 which is what you have. Maybe DM or PM him?

I've heard it's not needed, but given the PCM obtains gearing information from the BCM for its torque tables, it's hard for me to imagine how you won't run into issues like this with the traction control. Maybe if you turn it off it stops mattering?

 

[BimmerDriver]

My first thought was that a wheel speed sensor was left unplugged, which causes the car to think that you are losing traction and cutting back power. OP claims that no plug was missed, so maybe @ice445 has the right idea - just turn off traction control, and see how it performs.

I can see a world in which the computer thinks that you should be going XX MPH for YY RPM, which of course it uses for rev-matching and A10 downshifting, and with the dichotomy created by the new ratio, the computer says "these values are out of bounds" and limits power.

Remember the good ole' days, when all you had to do when swapping rear ends was change the speedometer gears?

Sponsored