The paper presents a fuel modulation attenuation model for single point closed-loop fuel metering systems. The model calculates the attenuation of a metered air-fuel perturbation and the time delay in the transport of the perturbed signal from the metering point through the engine to the exhaust system as functions of the modulation frequency, engine RPM, intake manifold vacuum, and exhaust gas recirculation. Results are shown for a V-8 engine with sine wave, triangular wave and square wave modulations. It is found that the attenuation for the triangular wave is the highest and that for the square wave is the smallest. It is also found that in general the attenuation increases with increasing modulation frequency and increasing EGR, but decreases with increasing RPM. The model can be extended to study the attenuation and transport delay of other engines and wave forms.