Fuel injection system

A fuel injection system 14 for a compression ignition internal combustion engine. The system comprises a fuel pump 20 comprising a pumping chamber 33, a first outlet valve 34 to control fuel delivery from the fuel pump to a primary accumulator 24 (common rail) in communication with fuel injectors. A secondary accumulator 40, and a second outlet valve 36 to control fuel delivery from the pumping chamber to the secondary accumulator. The first outlet valve controls communication between the accumulators, and the outlet valves are configured such that pressure in the secondary accumulator between pumping events is lower than in the primary accumulator. Lower fuel pressure in the secondary accumulator than in the primary accumulator means that pressure spikes in the pumping chamber are reduced, thereby reducing fatigue stress on components of the fuel pump. The secondary accumulator may also have pressure control means 50 with a leakage path 52 to a low pressure drain.