Question 9 OSE01 - Chief Engineer - OSV

The Correct Answer is C ### Explanation of Correct Option (C) **Why Option C is correct:** 1. **The symptom:** The engine is initially producing black smoke. Black smoke in a diesel engine indicates incomplete combustion, typically due to an air shortage or, more commonly during troubleshooting, an excess of fuel (too much fuel for the available air, or fuel being injected improperly and not burning). When troubleshooting a misfiring cylinder, this black smoke usually means one cylinder is injecting fuel that is not igniting or burning fully, and this unburnt fuel is carried out the exhaust. 2. **The test procedure:** The technician disables the fuel injector on a specific cylinder. By loosening the high-pressure fuel line fitting, fuel delivery to that cylinder stops. 3. **The result:** The engine previously producing black smoke now produces a clear stack. 4. **The conclusion:** This result proves that the **source** of the black smoke was the cylinder whose fuel supply was just stopped. If stopping the fuel supply eliminates the smoke, it means that cylinder was introducing fuel into the exhaust stream without adequately burning it (i.e., it was misfiring, or had very poor combustion efficiency). Therefore, the disabled cylinder is the faulty one. ### Explanation of Incorrect Options **A) After disabling the injector of a given cylinder, if the engine previously producing a clear exhaust now produces black smoke, this indicates that the cylinder associated with the disabled injector is misfiring.** * **Incorrect:** The premise states the engine is emitting black smoke (the symptom being investigated). More importantly, if the engine *previously* had a clear exhaust and *now* starts smoking after disabling a cylinder, this would generally mean the healthy cylinders are now being overloaded due to the loss of power from the disabled cylinder, causing them to smoke (or, less likely, the disabling procedure itself caused a problem). It does not diagnose the disabled cylinder as the original fault, especially since there was no smoke to begin with. **B) After disabling the injector of a given cylinder, if the engine previously producing black smoke now produces even denser black smoke, this indicates that the cylinder associated with the disabled injector is misfiring.** * **Incorrect:** If the engine was smoking and disabling a cylinder makes the smoke *worse*, it means the remaining operational cylinders are now bearing a higher load to maintain speed, often resulting in overloading and smoking themselves. This indicates that the disabled cylinder was likely a **contributor to power generation** and **not** the primary source of the original smoke. **D) After disabling the injector of a given cylinder, if the engine previously producing black smoke continues to produce equally dense black smoke, this indicates that the cylinder associated with the disabled injector is misfiring.** * **Incorrect:** If the smoke remains unchanged after disabling the cylinder, it means the fuel (and resulting poor combustion) from that specific cylinder was **not** the source of the visible black smoke. The source of the smoke must lie in one of the remaining operational cylinders.