3.55 gear install and SPEEDO CALIBRATION?

[GreenS550]

Actually it won't. It needs the learn from BCM box checked. Not sure if the tune was altered or if it is this way from the factory. I need a clean read of a 2020 and 2021

That isn't the area you change. I have repeated this several times. Look at the link and copy, paste. You are correct that the gear change is in the PCM, not the BCM which you can change with Forscan. And even then it is limited to certain ratios.
You change the tire size code in Forscan using the link information.

My experience on the gear change on the 2016 M6 is that the car started and ran fine, but at certain RPMs it backed off somewhat. Not full power. Not in all gears as well. Changing the tire size fixed perfectly.

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[ctandc72]

That isn't the area you change. I have repeated this several times. Look at the link and copy, paste. You are correct that the gear change is in the PCM, not the BCM which you can change with Forscan. And even then it is limited to certain ratios.
You change the tire size code in Forscan using the link information.

My experience on the gear change on the 2016 M6 is that the car started and ran fine, but at certain RPMs it backed off somewhat. Not full power. Not in all gears as well. Changing the tire size fixed perfectly.

I think you are misunderstanding what he showed you. That's not FORSCAN. He's using HPTuners software, which can change the tune.

He is saying that by default 15-17 Mustangs will auto learn the gear ratio, via data received by the BCM from the wheel speed sensor. It will auto learn up to the "max gear ratio" setting inside the ECU. That's 3.73 in this case. You can also turn off "learn from BCM" in the tune and manually put in the gear ratio.

 

[GreenS550]

He is saying that by default 15-17 Mustangs will auto learn the gear ratio, via data received by the BCM from the wheel speed sensor. It will auto learn up to the "max gear ratio" setting inside the ECU. That's 3.73 in this case. You can also turn off "learn from BCM" in the tune and manually put in the gear ratio.

Mine never learned the gear ratio. I drove it for many miles. If you google this, several Mustang owners have had this issue. on the S550 platform with manual or automatic transmissions. There is a sensor on the output shaft of the transmission that is in conflict with the ABS sensor. Changing the tire diameter (revs per mile converted into tire size) fixes this.

The ABS sensors deal with the speedo and when that data reaches the computer it sees this as a conflict with the PCM's gear ratio. The speedo is correct always as that input is from the ABS sensors.

 

[monte87]

This may be a dumb suggestion, but I thought the dealership service dept would be an option for the speedo and shift point recalibration.

I was having gear install done at a shop not dealer. I dont wanna get raperd via stealership

 

[br_an]

I was having gear install done at a shop not dealer. I dont wanna get raperd via stealership

I know, they're not known for being the low cost option, but with the shift points on the auto trans needing to be reprogrammed would you let just any shop do that?

 

[K4fxd]

If the shift points don't automatically change you could still go to the dealer and have it flashed for the gear.

 

[WildHorse]

Not true on my '17 Mustang or the several 15-17 Mustangs I helped swap pumpkins (steeper gears) in.

Check my build thread. No change to tune or anything needed. The car will auto learn the gear ratio from the BCM - according to what the max gear ratio setting is in the tune.

And I went from 3.15 to 3.55.

Then combo of gears/tires fell within the threshold for the BCM. Mine was 1% over and shit went south haha.

 

[K4fxd]

You have it backwards, it fell in the range programmed into the PCM.
Looks like 2020 and newer use calibration setting and not learn, so 2020 and newer will need a tune.

 

[WildHorse]

You have it backwards, it fell in the range programmed into the PCM.
Looks like 2020 and newer use calibration setting and not learn, so 2020 and newer will need a tune.

Tell that to my BCM. I'm telling ya it went all stupid.

 

[K4fxd]

The BCM doesn't care, it will just say wrong ratio entered if you hook up IDS or ForScan. The PCM parameters are what matter.

It's computers and software, sometimes they do not play nice.

 

[WildHorse]

The BCM doesn't care

I'm telling you it does. Go from 3.31 to a 3.73, throw some 28's all around on it then get back to me. But then again, what do I know ? I only just went through all that BS.

 

[ctandc72]

I'm telling you it does. Go from 3.31 to a 3.73, throw some 28's all around on it then get back to me. But then again, what do I know ? I only just went through all that BS.

It must vary then. I bought my '17 V6 brand new. 17" wheels / tires. Switched from 3.15 gears to 3.55 gears, and switch to 19" wheels and tires. Zero issues.

 

[K4fxd]

So what are you saying you did? Did your tuner send a new file? Did you use ForScan?

 

[WildHorse]

Yeah, that would be a tune. I don't have forscan.. yet.

 

[K4fxd]

So your tuner sent you a tune with the parameters that work with your gear and tires.

The box I circled and the one above it in the post where i showed the PCM stock parameters.

BCM sends info to the PCM and if that info is out of range you get the wrench light.

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