Question 54 MODE01 - Chief MODU Engineer

The Correct Answer is C **Why option C ("contaminated fuel") is correct:** The diesel fuel injection pump (or high-pressure pump) is a precision component operating with extremely tight tolerances, sometimes measured in microns. It relies on the lubricating properties of clean diesel fuel. When the fuel is contaminated with water, dirt, rust, or abrasive particles (like silica or metallic debris), these contaminants can cause significant damage: 1. **Abrasive Wear:** Hard particles quickly wear down the internal components (plungers, barrels, rotor, and cam surfaces), reducing the pump's efficiency and ability to maintain high pressure. 2. **Corrosion:** Water contamination leads to rust and corrosion, especially on steel components, which damages seals and precision surfaces. 3. **Clogging:** Fine particulate matter or microbial growth (diesel bug) can clog the internal filters, valves, and metering units, leading to fuel starvation or inconsistent output. Contaminated fuel is the single most common cause of premature failure in high-pressure diesel injection systems. **Why each of the other options is incorrect:** * **A) excessive engine vibration:** While extreme, prolonged vibration can eventually loosen fittings or cause fatigue, modern fuel injection pumps are robustly mounted and designed to withstand normal engine operating vibrations. It is not the primary or usual cause of internal pump failure. * **B) kinked fuel lines:** Kinked lines restrict the flow of fuel *to* the injection pump (low-pressure side) or *from* the pump (high-pressure side). This causes a symptom (engine stalling, low power) but does not usually cause catastrophic damage *to* the pump itself unless the restriction causes severe cavitation, which is less common than damage from contamination. * **D) improper adjustment:** While improper adjustment of timing or fuel rack settings can cause poor engine performance, high exhaust emissions, or overheating, it is an operational fault. It does not typically cause the physical, mechanical failure (wear, scoring, or seizing) of the high-pressure components that contaminated fuel does. Pumps often come pre-calibrated from the factory, making initial improper adjustment less common than in older, mechanically-timed systems.