Momentary camshaft speed signal of in-line fuel pump of diesel engines is investigated in this paper. First, time domain characteristics and frequency characteristics of camshaft speed are analyzed. Secondly, the relation between momentary camshaft speed and fuel pressure in the pump is studied. The work indicates that pulsed fuel pump pressure is a result of camshaft speed fluctuation. Thirdly, the relation among momentary speed fluctuations, different injection timing and injection duration are studied. Correlation of the fluctuation amplitude and injected fuel quantity is calibrated. The basic results show that it is possible to estimate cylinder-by-cylinder fuel injection quantity. Finally, the relation between camshaft dynamics and pump cam profile design is discussed. The results indicate that momentary camshaft speed is a useful signal for injection system design, diagnosis and control.