Change gear ratio 3:73 to 3:55 in PCM

[Glas86]

Hello my Name is Felix,

Iam new here to the forum. I did swap my 3:73 rear diff to a 3:55 just recently.
The car is a 2017 Manual GT. After the swap I experienced the car is not having power at certain RPMs in certain gears. That probably the ECU reducing power cause of calculated clutch slip based on the old gear ratio.

I tried to reprogram the gear ratio using forscan but I do not get the PCM to relearn the value. So all I get is a DTC from the PCM getting not valid data from the BCM when I change the value there.

Did someone successfully change the gear ratio using forscan?

Is there anyone in the Detroit area who could change that value in the PCM for me. I would drive to your place and also pay for the programming.
Or does someone know a good tuner who could do that for me?

Thanks!

Felix

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[EastTNMustang]

Hello my Name is Felix,

Iam new here to the forum. I did swap my 3:73 rear diff to a 3:55 just recently.
The car is a 2017 Manual GT. After the swap I experienced the car is not having power at certain RPMs in certain gears. That probably the ECU reducing power cause of calculated clutch slip based on the old gear ratio.

I tried to reprogram the gear ratio using forscan but I do not get the PCM to relearn the value. So all I get is a DTC from the PCM getting not valid data from the BCM when I change the value there.

Did someone successfully change the gear ratio using forscan?

Is there anyone in the Detroit area who could change that value in the PCM for me. I would drive to your place and also pay for the programming.
Or does someone know a good tuner who could do that for me?

Thanks!

Felix

Just so I understand...you were able to successfully change the gear ratio using FORScan, but you get a DTC error that is limiting your power in certain gears, correct?

Did you run the FORScan relearn procedure?

 

[Glas86]

The DTC U0422 in the PCM module just showed up after I changed the gear ratio in the BCM. The driving behaivior of the car was unchanged. I tried to run the relearn vehicle data routine for the PCM but that did not change anything.

Also if I change the gear ratio back to original the DTC disappeares.

 

[D24112]

What certain RPM and gears are you experiencing "not having power"?

 

[Glas86]

4th gear at like 2500 and at 3000 rpm and 5th around 2500. Once your beyond that rpm band everything is back to normal.

 

[EastTNMustang]

The DTC U0422 in the PCM module just showed up after I changed the gear ratio in the BCM. The driving behaivior of the car was unchanged. I tried to run the relearn vehicle data routine for the PCM but that did not change anything.

Also if I change the gear ratio back to original the DTC disappeares.

You are writing conflicting information...in your original post you state "After the swap I experienced the car is not having power at certain RPMs in certain gears."

So, are you experiencing driving issues in certain gears or not?

Confused.

 

[Glas86]

Yes I am having loss of power in certain gears at certains rpms. With the original gears setting in the BCM I do not have any dtc. When I change the setting in BCM I get the DTC but the driving behaivior does not change regardless. Before I swapped the gears all was fine. I swapped the hole pumkin and you can tell mechanically everything is correct sind ist working fine once you are above the rpm band where power is limited. The loss of power is independant of the DTC. It just seems like I do not get it to reprogram. I expect some kind of clutch protection algorithm to limit the power. Did anyone else experience this swapping gears?

 

[stang1971]

Had this happen to mine.... went from 315 to 373... used forscan to change it in the bcm.... i did the pcm relearn that forscan can do and all was fine after than.

 

[Glas86]

I tried this several times by now but it did not resolve that DTC. Do you have a 17 as well or was it a 15 or 16? How many modules should I see. Maybe my adaptor is bad and not establishing a connection to all modules? Should I see a TCM module?

 

[stang1971]

there is no TCM..... forscan can do a PCM relearn.

 

[D24112]

"That probably the ECU reducing power cause of calculated clutch slip based on the old gear ratio."

Do you have a reference that the ECU does that?

 

[EastTNMustang]

Had this happen to mine.... went from 315 to 373... used forscan to change it in the bcm.... i did the pcm relearn that forscan can do and all was fine after than.

I had the same thing on my 17 when I did a speedometer correction...in 4th gear car would fall flat, no acceleration. Did the PCM relearn in FORScan and everything back to normal with full acceleration available in all gears.

 

[Cobra Jet]

Have you posted in the Forscan DIY thread and other question is, are you using the most recent Forscan software?

 

[Glas86]

No I have not yet postet in the Forscan threat. I was using the latest Forscan. Maybe I should try an older version where this feature just got introduced. I have a Elm327 adaptor with that toggle switch.

It seems like the relearn routine doesn’t work at my setup right now. Which version of forscan did you use when it was confirmed working?

 

[Cobra Jet]

No I have not yet postet in the Forscan threat. I was using the latest Forscan. Maybe I should try an older version where this feature just got introduced. I have a Elm327 adaptor with that toggle switch.

It seems like the relearn routine doesn’t work at my setup right now. Which version of forscan did you use when it was confirmed working?

Yea, I’ve heard of certain instances of Forscan not working after updates or revisions, as well as possible adapter compatibility concerns too. Hit up the Forscan thread in the DIY sub forum on here; it’s a huge thread:
https://www.mustang6g.com/forums/showthread.php?t=61773

You might just be having a software issue with the Forscan version you’re running.

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