Pumping losses occur during the intake stroke. In conventional engines the throttle is nearly closed when the engine is under light load and that increases pumping loss. Pumping loss can be reduced by allowing large amounts of air into the cylinders which makes the mixture very lean. In other words the volume of injected fuel remains the same while the volume of intake air increases.
Mitsubishi is even further on with the concept and a direct injection petrol car is already on sale in Japan. The 1.8 litre engine will power a Carisma in 1997.