HPOP replacement parts and performance upgraded pumps give the 7.3 Powerstroke more power by recovering what's been lost. This HPOP system delivers high pressure oil that is critical for the injection cycle. The HPOP system on the 7.3 is a high pressure system separate from the low pressure engine oil system that lubricates the engine. The high pressure system creates up to 3000 psi that is used to fire the fuel injectors. Lower than 2700 psi from a weak system will cause loss of power and fuel economy. Low pressure is hard to diagnose without the proper equipment. The HPOP is basically a hydraulic pump and weakens slowly over time. The most popular HPOP upgrade is the 7.3 adrenaline pump.