Originally developed by Caterpillar in the early 90’s the 7.3L Power Stroke had a Hydraulic Electronic Unit Injector (HEUI) system which changed the Diesel engine game with electronic control and no longer using mechanical systems. Electronic control meant that within an injectors operating range the system had infinite control which resulted in cleaner emissions and greater fuel economy potential.

HEUI systems are based off of the simple concept of leverage and force multipliers applied to hydraulics. The input pressure is supplied via high pressure engine oil in a high pressure oil system fed from the engine oil via a High Pressure Fuel Pump (HPOP) which feeds each injector with a steady supply of high pressure oil. The electric injectors utilize a solenoid to control oil flow into the top of the injector via a poppet valve. High pressure oil introduced into the injector presses on a separator intensifier piston which comprised of a piston separating the oil chamber from the fuel chamber that pushes on a plunger that compresses the fuel in the fuel chamber within the injector. The more the oil pressure introduced the higher the pressure of the fuel. The fuel plunger exponentially intensifies the input oil pressure to create greater output fuel pressure from the fuel pressure down to the injector nozzle valve. When the injector is ready to fire an electronic is sent to open the nozzle valve and fuel enters the cylinder.

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7.3L Power Strokes use “A” code injectors with a 16mm intensifier piston and a 6mm plunger. When replacing an injector it is important to identify your Injector Code and replace with the correct Injector. The older 7.3 utilized single shot injectors while the newer models changed to a split shot injector for a quieter running engine and improved emissions.

Unlisted in the chart is code AC “high torque” injectors used in buses and heavy commercial 7.3 non PSD engines (International). These are single shot injectors with a 160cc flow rate.