Tuning software can only tune the air/fuel ratio for open loop operation.

• A. True
• B. False
• C. It depends
• D. Not applicable

Answer: (D)

Understanding how tuning software affects fuel delivery requires separating open-loop and closed-loop operation. In open-loop, the engine relies on a pre-set fuel map, so adjusting that map directly changes the air/fuel ratio. In closed-loop, the ECU uses feedback from the O2 sensor to correct fueling, so changes in the map may be overridden by the feedback unless you adjust the closed-loop behavior (enable or disable it, change the target lambda, or modify trims). Because different ECUs and tuning tools handle these modes differently, there isn’t a single universal rule about what the software can tune. Some platforms let you tune AFR in open-loop, others let you influence closed-loop fueling too, and some limit tuning to one mode. Therefore the statement isn’t universally applicable; the best fit among the options is that it’s not applicable.