A method of reducing emissions from a large, medium speed fuel injected diesel engine of the type used on locomotives subject to transient modes of engine operation in which the engine is accelerated or increased loads are applied. The method comprises: monitor at least one operating parameter of the diesel engine; determining, based on such operating parameter, whether the diesel engine is in a transient mode; and controlling a timing of fuel injection to cylinders of the engine, to retard the timing when the diesel engine is in a transient mode relative to the timing of fuel injection when the diesel engine is not in a transient mode of operation.