In the later models of B Series Engine, the fuel system was switched from mechanical injection and timing to mechanical injection with electronic timing. This was all thanks to Bosch's new VP44 injection pump. The VP44 injection pump is driven at half the camshaft speed and produces fuel pressure at about 4,500 psi to pop the vertically centered injectors in the engine.  These injection pumps need to have constant fuel pressure behind them of at least 10psi at all times to maintain the priming of the system. If you run these pumps dry it can cause your pump to fail quickly. The VP44 injection pumps were the first pumps placed in the Cummins engine to have an FPCM. FPCM stands for the fuel pressure control module, and this is responsible for maintaining and controlling the fuel pressure of the system. However, even though this new technology to control fuel pressure was convenient, it had a major downfall. The problem was them was that they were unable to be serviced without replacing the entire fuel pump. Another important piece of the puzzle that is responsible for the longevity and functionality of the VP44 was the fuel transfer pump mounted on the side of the block next to the ECM. This electronically driven vane pump is what supplies that minimum of 10psi to the injection pump so it maintains constant fuel pressure as well, as cools itself, and lubricates itself.