How can ECU timing be miscalibrated, leading to incorrect fueling?

• A. Using lower octane fuel causes ECU timing to miscalibrate.
• B. Sensor faults (MAP/MAF/ECT), calibration drift, or software corruption can shift fuel maps or timing.
• C. Ignition timing is the only factor.
• D. Ambient temperature has no effect on ECU calibration.

Answer: (B)

The ECU determines fueling and timing from sensor data and its internal fuel maps and timing tables. If a sensor like MAP, MAF, or ECT provides faulty or drifting readings, the ECU will apply the wrong fuel amount and timing. Software corruption or calibration drift can also alter the stored maps or timing values, so the engine ends up running with incorrect fueling. These are the direct ways miscalibration happens.

Lower octane fuel doesn’t directly recalibrate the ECU; it may cause the ECU to pull timing in response to knock, but that’s an adaptive effect, not a miscalibration of the timing map itself. Ignition timing isn’t the only factor—the ECU uses sensor inputs to shape fueling as well, and ambient temperature can influence sensor readings and compensation. The important idea is that sensor faults, drift, or software issues can shift the fueling maps or timing, leading to miscalibration.