Tuning fuel using STFT only?

In the Hyundai world, remote tuning has just become a reality. While the tools available do allow an analog input for logging data from a wideband, it's not used or well understood like on other platforms.

The tuners are using the short term fuel trims to gauge the fueling requirements. What is it that they are expecting from this? How would this process differ from a factory tune ecu vs an already tuned ecu?

In this case, lambda is not available nor logged, so how reliable is this method and how are they doing it?

These are the PIDs that are logged

• Engine RPM

• Vehicle Speed

• Engine Load

• Absolute Throttle Position

• Engine Coolant Temperature

• Short Term Fuel Trim

• Ignition Timing Advance

• Intake Manifold Absolute Pressure

I've always been cautious of remote tuners that do not have access to a lambda reading. I have tuned a 17 Camaro SS on flex fuel using only STFT, but having a wideband was absolutely essential. Disabling the LTFT in my case was to prevent LTFT from affect WOT fueling. Curious if anyone knows an answer to this. Sub'd

I'm not familiar with the Hyundai platform so it's hard to offer much help. If the engine is only fitted with narrowband O2 sensors then you're only going to be able to use the STFT for tuning under idle/cruise conditions and will still need a wideband for WOT/open loop tuning. If on the other hand the engine uses wideband sensors and runs constantly in closed loop control then the STFT can be used. The issue would be that you're then making the assumption that the wideband sensor is accurate under WOT operation and often factory sensors aren't. At a minimum I'd recommend comparing the factory wideband sensor to a known AFR meter to ensure it's correct.