An engine control system and method maintains an optimum exhaust fuel to air ratio in an internal combustion engine. A secondary air injection (SAI) pressure is measured in an SAI system. The SAI pressure measurement is converted into an SAI flow value. A fuel compensation value is obtained based on the SAI flow value. Fuel delivery is compensated to the engine based on the fuel compensation value. In a second embodiment, the fuel compensation value is obtained based on the SAI pressure measurement. Fuel delivery is compensated to the engine based on the fuel compensation value. In a third embodiment, a primary flow value is calculated at an air intake of the engine. A fuel compensation value is calculated based on the SAI flow and primary flow values. Fuel delivery to the engine is compensated based on the fuel compensation value.