Switch on the fly (SOTF) tuning, also known as "on-the-fly" tuning, map switching or

dynamic tuning, allows drivers to change performance settings and engine parameters

while the vehicle is running. Tuning a diesel engine with SOTF tuning is a constant trend

that has been going on for many years. While this feature can be convenient and

provide some flexibility, there are downsides and risks associated with SOTF tuning. 

Through the past 20 years or so, we've tested and helped develop "switch on the fly"

(SOTF) tuning for multiple vehicles. The first, was the 6.0L which we used the Bully Dog

GT software, which eventually migrated into the SCT Livewire, after the merger. After

that, we worked with HP Tuners on their SOTF option for the 6.0L. All of these options

are available today and work decently for a stock truck and low power tuning, which

doesn't require special tuning to the transmission to handle the power change.

Specifically, multiples of the same tune. For instance a 50hp, 65hp, and 75hp Tow or a

75hp, 100hp, or 150hp. I'll mention this in more depth later in the article, but you lose

the benefits of SOTF when you need to flash the transmission file for major power

changes. Major power changes is the real reason to change the tuning, a Tow file to a

Street file for example. We do offer SOTF tuning, but only for power level changes

within reason.  In most cases, about 90%, we've found SOTF not being worthwhile for

customers.  Due to this reason, companies like HPT and SCT haven't worked on

developing any new switching options.  Even on gas vehicles, the switchable options

are limited to fuel content, launching RPM, and in some cases boost via a boost

controller.

This brings us to the myth's of SOTF tuning. We will take the 6.0L Powerstroke as an

example. The 2003-2007 6.0L ECU has very limited space for any additional tables,

changes, or pointers. The 2003-2004 has the least amount and 2004.5-2007 has

slightly more, still not enough to do what's needed. To get around this, companies like

HP Tuners and BullyDog/SCT have added a limited number of tables in the ECU and a

torque reference table so the transmission is aware there's less torque. For a stock

truck with lower power, it works well. You can have moderate shifting changes, so it

covers your performance option, down to your tow program. However, if you need to

tune the trans for the varying power options, there's no real benefit to SOTF.

Additionally, your unable to correctly manipulate torque to the trans, limiting torque from

the highest level is the only option. This doesn't actually change shifting characteristics.

To change shift points, RPM, firmness, slip time, converter lockup, the list goes on and

on...you'd need to change power on the fly on the transmission as well. 

In short, when SOTF program is installed to your ECM, your transmission doesn’t

actually change with it. At that point, with constant variables in torque at every throttle

positions, it takes a lot of time for the transmission to “learn” the shifting patterns and

get used to the constant varying power at unusual load and throttle. If this power level is

constantly being limited and increased by the switching, but the ECM is stuck with a

single tune file to try and interpret that input, the shifting patterns will be erratic,

inefficient, and even dangerous and/or damaging to the transmission. 

On the newer vehicles, the switches are actually torque limiters only. This is most often

done by tricking the fuel temp or air temp sensor readings. The reasoning for this being

a poor and unsafe option, is the same reason for the older trucks, like the 6.0L. 

In gas applications, like Ford Ecoboost, Nissan GTR, BMW, Audi, etc. the SOTF is

normally a map based change to boost and sparkn for varying fuel quality and

ethanol content. While the power can change drastically, it's within a specific power

level that allows for similar torque in each setting, mainly increasing top end

horsepower.  For a DCT and Manual vehicle, this works very well.  For a normal

automatic with a converter, the trans needs to be setup for max power in all instances.

For Diesel vehicle all of these options are not viable for a complete tune and cause

more issues than the older trucks can already be plagued with.