A method is disclosed for controlling operation of an engine coupled to an exhaust treatment catalyst. Under predetermined conditions, the method operates an engine with a first group of cylinders combusting a lean air/fuel mixture and a second group of cylinders pumping air only (i.e., without fuel...http://www.google.co.uk/patents/US7047932?utm_source=gb-gplus-sharePatent US7047932 - Method to improve fuel economy in lean burn engines with variable-displacement-like characteristics
