Forscan and SCTX4 tuner hesitation issue

[FABMAN]

Last night I had a buddy of mine adjust the tire size on my Gt with Forscan. After the change the speedo was dead on but it now has a stumble/hesitation when driving aggressively.

I did some research and found this post on forscan.org (https://forscan.org/forum/viewtopic.php?t=15465)

“…Forscan makes vehicle option changes.
Tuners change the engine/transmission calibration.

There is one area they overlap, final gear ratio and tire sizes, AKA the VID block info.Here is why:

The tune has the option to use the VID block gear ratio/tire size, OR those can be specified in the tune itself. But here is the catch: it is one or the other. So if your tuner is setup to use gear ratio from the tune, you MUST adjust it from the hand held device or tuning software.

If your tune setup to use the VID block, you MUST use Forscan or IDS to calibrate the speedometer for gear and/or tire size changes. Its is one or the other.

I have stopped using my SCT x4 to calibrate my speedo, as it requires a reflash (takes long lol) I now have my tune setup to use the VID block data. It takes about 30 seconds to make a tire size change w/Forscan. And since it is not a reflash of the PCM, there is no chance of bricking my PCM for a tire size change.”

So it looks like this may be the route of the issue. I am going to restore my tire code to stock to see if this alleviates the condition. If so, here is my question. Can a Dyno tuner like Diego adjust for my tire size using my SCTX4 instead? Also, should I flash the tune back to stock or just leave as it was and just restore the tire code with forscan?

[ZR]

Best to call him to discuss and quit driving until it's running properly.

[FABMAN]

Best to call him to discuss and quit driving until it's running properly.

Spoke with Diago today and booked an appointment for the 23rd. On his advice we will restore the tire size code tomorrow to see if drivability comes back. Then I will allow him to tune for tire variance at my dyno appointment.

Hoping it lays down some really stout numbers…

Here’s the next question, keep the tune for 91 or move up to a 93 tune. I am not worried about the minor fuel cost difference just want the best blend of performance and drivability.

[ZR]

If it was mine, all in brother.

[FABMAN]

Happy to report that we restored the tire code and the car has returned to normal.

Hoping Diago can work his magic and also adjust for the tire size in the custom tune so my speedo reads accurately again. Will update after my appointment on the 23rd.

[Zippy]

93 all the way

[FABMAN]

So update to this thread.

SCTX4 cannot adjust for tire size on the S550 Mustangs as the tire size resides in the BCM. So there is a very good thread on Mustang 6g that explains the process.

Here is the thread:https://www.mustang6g.com/forums/threads/correct-your-speedometer-error-no-flash-or-tune-required.67564/

For those of you who don’t want to read 11 pages of notes I can basically pick some parts of the thread and sum it up here but for complete instructions read the first page or two of the M6g thread.

You will need a laptop running Windows, the free FORScan software with a free extended license, and some sort of ODB reader that works with FORScan and plugs into the laptop.

For 2015-2019 Mustangs, Ford programs the tire size of the car on BCM line 726-12-01 in the second four-digit block of hex.

For 2020+ Mustangs, it's split between 726-15-01 and 726-15-02 as described in the original thread. It's stored as the nominal circumference of the driven wheel in millimeters with a revs/mile conversion factor of 96.7%.

Spart at M6g even provided a calculator (https://docs.google.com/spreadsheets/d/1mWnuQZlDTUGjKjmJje1QJIR8Z2c7Kf8KBZxKnw_8EqU/edit#gid=2133040050)to help you find the correct value.

You WILL get a non-MIL DTC P160A (Control Module Vehicle Options Reconfiguration Error) when you change this in the PCM. What you want to do is go into the computer-chip-looking tab in FORScan where you normally edit as-built. At the top, you'll see a new function for the PCM - "Module initialization/relearn vehicle data“.

Once you do this PCM relearn, codes will be cleared. Take for a spin and rescan for DTCS and you should be good. This all sounds far more difficult than it really is. It’s actually pretty straightforward.

Again, I do not take any credit for this information as it was all provided by Spart at M6g.

Here is the catch though (from my experience)…if running a stock tune the car is happy, speedometer is accurate and all is well. Load a custom tune that tries to account for tire size and it appears drivability issues return.

I will be back with Diogo (who has been great by the way) in the spring to find the fix for this as we have simply run out of season and he is moving locations.

Wanted to share with the TMC in case any other S550 owners here go down this path.

[ZR]

Great info, thanks for posting Fab.

[Stephen06GT]

How far off is the speedo/odo reading if you don't adjust for tire size in the custom tune?

[FABMAN]

How far off is the speedo/odo reading if you don't adjust for tire size in the custom tune?

Speedo is off by 3.6% too fast. So it is essentially adding some "ghost mileage" to the Odo when not adjusted. In current state the car is dead on for speedo (GPS verified over a couple of apps and verified on the dyno as well).

[Stephen06GT]

Speedo is off by 3.6% too fast. So it is essentially adding some "ghost mileage" to the Odo when not adjusted. In current state the car is dead on for speedo (GPS verified over a couple of apps and verified on the dyno as well).

Personally, for that kind of difference, I wouldn't worry about it.

[FABMAN]

Personally, for that kind of difference, I wouldn't worry about it.

I hear you but I believe that if there a solution to a problem then why avoid learning by taking a work around. Plus I am not the only S550 owner with a tune and aftermarket wheels.

In fact my buddy with blue Cervini 17 GT PP1 that comes to track day did the same Forscan adjustments and is running identical tire sizes as I am with no issues so I know a solution is there. His car is running a Ford Performance Power Pack 3 tune without any issues or codes.

At this point I feel like we are on the verge of a solution that is only going to be delayed by a winter pause. In the spring we should be able to figure out the solution as I strongly believe it is already listed in my original post.

[Zippy]

No wonder all these coyote guys think they are fast, speedo reads too fast. :stickpoke::stickpoke::stickpoke:

[Stephen06GT]

Don't Trust Your Car's Speedometer

https://www.roadandtrack.com/car-culture/car-accessories/a32026968/are-speedometers-accurate/

[ZR]

Interested to hear how it plays out in the end.

[FABMAN]

Update on this thread. Went to see Diago at his new location. Really nice new setup and it’s great to see DCT back to making Toronto Mustangs faster than ever!

I believe we found the missing piece of the puzzle today and I am happy to report that it appears my drivability issues are now a thing of the past. Speedo is now accurate and the car runs like a freight train!

The issue was that the software needs to be told to accept the axle values so the PCM doesn’t fight with the BCM. Once he configured it that way the problem appears to have been fixed!

So I would recommend if you have an S550 Mustang with aftermarket wheels and tires that have been adjusted to reflect accurate speedometer readings with Forscan go see Diago.

He will get your tune done, wake the car up and you can avoid issues as it looks like we figured it out.

Big thanks to Diago and the DCT crew for patiently working with me to get this sorted.