Use of dilution with exhaust gas recirculation (EGR) in spark ignition (SI) engines offers substantial efficiency gains, especially, when boosting and downsizing is employed. However, the onset of instabilities in engine operation, due to misfires and partial burns, limits the dilution levels. Control models can be employed to improve engine stability during high dilution operation, and spark and fueling are one of many control parameters available for cycle-to-cycle control implementation. This paper aims to understand the sensitivity of the combustion process to changes in fueling at various dilution levels achieved with both excess air (lean operation) and EGR. Sinusoidal perturbation was introduced into the injected fuel quantity and the sensitivity to this perturbation was characterized using a fast Fourier transform (FFT) analysis of the cycle cumulative heat release data. Furthermore, the minimum fueling change required to significantly affect engine operation was quantified at various levels of dilution.