A common rail diesel engine is experiencing rough idle and misfires, particularly noticeable when cold. The HDET tests the fuel injectors and finds that one injector's opening pressure is 40 MPa while the specified opening pressure is 150 MPa. Which of the following is the most appropriate action for diagnosis?

Question: A common rail diesel engine is experiencing rough idle and misfires, particularly noticeable when cold. The HDET tests the fuel injectors and finds that one injector's opening pressure is 40 MPa while the specified opening pressure is 150 MPa. Which of the following is the most appropriate action for diagnosis?

Answer options: ✅ Replace the faulty injector, as its opening pressure is significantly below specification.

• Increase the common rail pressure to compensate for the low injector opening pressure.
• Adjust the engine's fuel injection timing to compensate for the weak injector.
• Check the engine's glow plugs, as this issue may be related to cold starting.

Correct answer: Replace the faulty injector, as its opening pressure is significantly below specification.

Explanation: The opening pressure of a common rail injector is crucial for proper fuel atomization and spray pattern. If an injector opens at 40 MPa instead of the specified 150 MPa, it will spray fuel poorly, leading to incomplete combustion, rough idle, and misfires. Replacing the faulty injector is the direct and correct solution as the injector itself is defective and cannot be adjusted. Glow plugs warm the cylinder, but won't fix a mis-spraying injector.