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In this work we have developed an algorithm to estimate and control the air fuel ratio of each cylinder from the measurement of an UEGO sensor placed at the confluence point in the exhaust manifold. In our case of study the exhaust manifold was very asymmetric. We have developed a simple model of this exhaust manifold capable of satisfying the control objectives. The lambda value for each cylinder is predicted from the actual lambda value measured at the confluence point by 4 different static Kalman filters depending on the cylinder that has finished its exhaust phase. The lambda feedback uses the output of the Kalman filters to control the AFR for each cylinder. The algorithm has been implemented on a production SAGEM ECU and the experimental tests have been made on a PSA 1.8 liter 4 cylinder engine The experimental results show that the algorithm is able to correct the cylinder to cylinder AFR with an accuracy around 3% for a fueling variation of 30%.