Final answer:
The 4-step injection actuation pressure test sequence in a HEUI system checks the injector pressure regulator valve and high-pressure pump. This test ensures the fuel injection system properly regulates fuel pressure for optimal engine performance.
Step-by-step explanation:
When performing a 4-step injection actuation pressure test sequence on a typical HEUI (Hydraulic Electronic Unit Injector) system, the components being tested are the injector pressure regulator valve and high-pressure pump. This test is crucial for ensuring that the fuel injection system delivers the correct amount of fuel with the proper pressure during engine operation. The HEUI system relies on oil pressure to actuate the fuel injectors, and the injection pressure regulator valve works in tandem with the high-pressure pump to control this pressure. The 4-step test sequence is designed to check the system's performance under different conditions and identify any issues with the pressure regulation or the pump's ability to generate the required pressure.