While performing a back-leakage test for a first-generation Bosch common rail fuel system, the fuel volume was measured to be above specification.

Technician A says the cause could be a leaking quill tube.

Technician B says the cause could be one or more injectors with worn-out ball valve seats.

Who is correct?

Both Technician A and Technician B could be correct, as a leaking quill tube or worn-out ball valve seats in the injectors can lead to a higher than specified fuel volume in a back-leakage test for a Bosch common rail fuel system.

Explanation:

The student has asked a question regarding a back-leakage test for a first-generation Bosch common rail fuel system, where the measured fuel volume was above specification. The potential causes suggested involve leaking components or worn-out parts within the fuel system. Technician A suggests that a leaking quill tube could be the cause of the excess fuel volume, while Technician B believes that the issue may be due to one or more injectors with worn-out ball valve seats.

Both technicians could be correct in this situation. A leaking quill tube could certainly allow fuel to bypass the intended flow path, resulting in a higher measured volume during the test. Similarly, injectors with worn-out ball valve seats could also cause additional fuel leakage, contributing to the volume being above the specified limit. Diagnosing the precise issue would likely require further inspection of these components.

When diagnosing fuel system issues like this, it's important to consider all potential sources of leaks or wear that could impact the measurement of fuel volume during a back-leakage test.