Unlike common-rail systems that use complex electronics, the PT injector is a mechanical marvel. Its operation is based on two key principles: pressure and time.
Fuel is supplied to the injector by the gear pump at a pressure that varies based on engine speed and throttle position. Inside the injector body, a plunger is pushed down by the camshaft. However, fuel doesn't enter the combustion chamber until the very end of the plunger's stroke.
Here’s a simplified breakdown:
Metering: As the plunger rises, fuel enters the injector barrel through a metering orifice. The pressure of the fuel (determined by the PT pump) controls how much fuel flows into the injector during the time the inlet port is open. Higher pressure = more fuel.
Injection: When the plunger is forced down by the cam, it initially pushes fuel back through the inlet port (bypassing). Once the plunger covers the inlet port, the trapped fuel is then forced out through the injector tip at incredibly high pressure, atomizing it for combustion.
Pressure and Time: The amount of fuel injected is a direct result of the fuel pressure (controlled by the pump) and the time the metering port is open (which is determined by engine RPM).