Question 18 AEL01 - Assistant Engineer - Limited

The Correct Answer is A **Explanation for Option A (Correct):** Option A states that the cylinder associated with the disabled injector is firing properly, but at least one other injector is misfiring. This is indicated by the results of the troubleshooting test: 1. **Before Disabling:** The engine is running rough and producing large amounts of black smoke. Black smoke signifies incomplete combustion, usually due to an excess of fuel relative to the available air, or poor atomization/timing, indicating misfiring or overloading elsewhere in the engine. 2. **After Disabling (Loosening the line):** The engine runs **even rougher**. This key response means that disabling the injector removed a functioning cylinder from the power production cycle. If the cylinder were already misfiring (i.e., not contributing power), disabling its fuel supply would not make the engine noticeably rougher, and might even slightly improve the overall combustion/smoke if that cylinder was contributing to the black smoke. Since performance worsened, the cylinder was contributing power, meaning **it was firing properly.** 3. **Smoke Production:** The engine **continues to produce equally dense black smoke**. If the cylinder that was disabled was the *only* cause of the black smoke (due to, for example, over-fueling or poor atomization), the black smoke production should have significantly decreased or stopped when its fuel was cut off. Since the dense black smoke persists after disabling this functioning cylinder, the source of the persistent incomplete combustion (misfiring/poor combustion causing the black smoke) must lie with **at least one of the remaining, active cylinders.** Therefore, a functioning cylinder was disabled (causing the engine to run rougher), and the underlying black smoke problem (incomplete combustion) persisted (indicating other misfiring cylinders are the source of the smoke). **Why Options B, C, and D are Incorrect:** * **B) This indicates that the cylinder associated with the disabled injector is firing properly, and all other injectors are firing properly.** * This is incorrect because the persistence of the equally dense black smoke indicates that the systemic problem of incomplete combustion (misfiring/poor firing) is still occurring in the remaining active cylinders. If all other injectors/cylinders were firing properly, the black smoke would have ceased or significantly decreased upon disabling the potentially over-fueling cylinder, or if the initial smoke was due to simple overloading (which would lessen as power output dropped). * **C) This indicates that the cylinder associated with the disabled injector is misfiring, and at least one other injector is misfiring.** * This is incorrect because if the cylinder associated with the disabled injector were misfiring (not contributing power), disabling the fuel would generally not make the engine run *even rougher*. It would either have no effect or slightly improve the situation (if it was the source of the initial black smoke). The worsening performance proves it was firing properly. * **D) This indicates that the cylinder associated with the disabled injector is misfiring, but all other injectors are firing properly.** * This is incorrect for two reasons: 1) The engine running even rougher proves the disabled cylinder was firing properly (not misfiring). 2) The persistence of equally dense black smoke proves that the remaining cylinders are *not* all firing properly, as they are the source of the continuing black smoke.