The 7.3L and 6.0L Power Stroke engines are somewhat unique in that they use oil pressure to run their fuel injection systems. The system was created with a joint venture between Caterpillar and International in the early 1990's. The system can be found on many heavy-duty and medium-duty engines, not only in the 6.0L or 7.3L. It was an ingenious system, with one of the biggest positives being that it made it impossible to run the engine with no oil, preventing a lack of oil pressure related engine failures. Now, a little more on how these systems work:

Oil Pressure. Hydraulic Electronic Unit Injection (HEUI for short) systems used in Power Strokes take a 25-75 psi supply of oil from the low-pressure oil pump (LPOP) located on the crankshaft. The HPOP then turns that pressure to as high as 4000 psi in the 6.0L. The pressure supplied from there is regulated via the Injection Pressure Regulator (IPR) and sent through the HPOP lines to oil galleries in each cylinder head. Those galleries supply each injector with high-pressure oil. Separate galleries in each head also receive a supply of fuel from the lift pump at roughly 60 psi, and send that supply to each injector.

Fuel Pressure. A few things must happen inside each injector to reach that 21,000 psi. First, high-pressure oil pushes down on the intensifier piston, which pushes on the plunger (which has fuel below it, under the aforementioned 60-ish psi); due to the different size piston and plunger (7:1), the fuel pressure to the nozzle reaches upwards of 21,000 psi (depending on demand requested from the engine's computer, the IDM). And finally, that fuel is sprayed into the combustion chamber, making power.

Maintenance. Now, lets talk for a second about how to keep a HEUI system equipped 6.0L or 7.3L running well.

Good Oil. All these parts we've talked about require good clean, and cool oil. Running a high quality oil, and changing it often is key. You will notice a huge difference in how your truck runs after a good oil change. Even though most vehicles require 5000-10,000 mile oil changes these days, we still change the oil in our 6.0L or 7.3L trucks every 3000 miles as oil in 7.3's and 6.0's goes through more stress than with any other engine (due to the HEUI system's high pressure).

Quality Parts. Cheaply made knockoff pumps, injectors, HPOP lines, or sensors are everywhere nowadays. Always make sure you're getting your parts from a reputable source (like Riffraff Diesel!!). HPOP lines are one of the most common things we see fail when not built correctly. The fittings on cheaply made lines leak and the hoses rupture after not that long of use. Spend the money on something that won't leave you stranded and you'll thank yourself for years to come.