Which faults can cause ECU fueling miscalibration when faulty?

• A. Only a faulty MAP sensor can miscalibrate fueling.
• B. Sensor faults (MAP/MAF/ECT), calibration drift, or software corruption can shift fuel maps or timing.
• C. Ignition coil failure only affects spark, not fueling.
• D. Using diesel in a gasoline engine has no effect.

Answer: (B)

Fuel metering depends on accurate sensor data and correct fuel maps in the ECU. If any input or the map itself is off, the ECU will misjudge how much fuel to deliver, leading to fueling miscalibration.

Sensor faults such as MAP, MAF, or ECT can directly skew the ECU’s view of engine load, air mass, or temperature. A bad MAP or MAF makes the ECU think the engine is drawing more or less air than it actually is, so it adjusts fuel delivery in the wrong direction. A faulty ECT can disrupt warm-up enrichment and fueling trims based on coolant temperature. When these readings are incorrect, the fueling map or the timing decisions derived from them shift away from the intended targets.

Calibration drift is another cause. Over time sensors drift, and the ECU’s fuel maps or trims may no longer align with the engine’s real behavior, producing persistent lean or rich conditions even though the sensors themselves aren’t failing outright.

Software corruption is a more systemic issue. If the ECU’s software or calibration data are corrupted, the fuel maps or timing tables can be altered, causing incorrect fueling across operating conditions.

Ignition coil failure affects spark and can cause misfires, but it does not directly change the ECU’s fueling calibration. Likewise, using diesel in a gasoline engine is an extreme scenario that disrupts operation but isn’t about normal fueling calibration faults.