The name "PT" stands for Pressure-Time, which is the fundamental principle of its operation. Unlike common rail systems that use high-pressure pumps to "push" fuel into the cylinder, the PT system is a "pull" system based on flow.

Here’s a simplified breakdown:

• Fuel Flow: The PT pump delivers fuel at a low pressure (typically 5-20 psi during cranking and up to 120-145 psi at full load) to the injectors through a common rail.

• The Metering Phase: As the injector plunger is pushed up by the rocker arm cam, it opens a metering orifice. The amount of fuel that flows into the injector cup is determined by the Pressure from the pump and the Time the orifice is open (hence, Pressure-Time). Higher pump pressure (from engine RPM/load) allows more fuel to flow in during that short time.

• The Injection Phase: The cam rotates further, and a strong spring forces the plunger back down with immense force. This traps the metered fuel and violently squirts it through the injector tip into the cylinder. The injection pressure is created mechanically within the injector itself, not by the pump.

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