Question 32 OSE02 - Assistant Engineer - OSV

The Correct Answer is A. **Explanation of Correctness (Option A):** Option A describes the standard and correct procedure for bleeding air from the high-pressure fuel lines in a diesel engine equipped with a multi-plunger injection pump (which is typical for generator drive engines on supply boats). 1. **Slackening the Fitting:** To allow the trapped air (which prevents injection) to escape, the connection at the highest point of the line, which is usually the injector fitting, must be slightly loosened (slackened). 2. **Generating High Pressure:** Air in the high-pressure lines can only be effectively pushed out when the injection pump is actively producing high pressure. This happens only when the engine is actively rotating (cranking) using the starter motor. The manual priming pump (B and C) only operates on the low-pressure side (up to the injection pump) and cannot generate the necessary pressure (often thousands of PSI) to bleed the high-pressure lines efficiently or correctly. 3. **Observation and Retightening:** The goal is to remove all compressible air. Once a "solid stream of fuel" (pure, air-free diesel) is observed spurting out of the loosened fitting, it confirms the line is purged, and the fitting is immediately tightened to restore the necessary injection pressure for the engine to start and run. **Explanation of Incorrect Options:** * **B) Slackening each high-pressure fuel line fitting at the fuel injector while stroking the manually operated priming pump and allowing air to escape, then retightening when bubbly fuel is observed.** This is incorrect because the manual priming pump only generates low pressure and is ineffective for purging the high-pressure lines. Observing "bubbly fuel" is also incorrect; the line must be fully purged until a *solid* stream is seen. * **C) Slackening each high-pressure fuel line fitting at the fuel injector while stroking the manually operated priming pump and allowing air to escape, then retightening when a solid stream of fuel is observed.** This is incorrect because, like Option B, the manually operated priming pump cannot generate the high pressure required to correctly purge air from the high-pressure lines leading from the injection pump to the injector. * **D) Slackening each high-pressure fuel line fitting at the fuel injector while cranking over the engine with the starter and allowing air to escape, then retightening when air bubbly fuel is observed.** This is incorrect because while cranking the engine is the correct method to generate high pressure, the technician must continue the process until a *solid* stream of fuel is observed. Retightening while the fuel is still "bubbly" means air is still present, and the engine will fail to start or run poorly.