Question 10 UFIV02 - Assistant Engineer - UFIV

The Correct Answer is B **Explanation of why Option B is correct:** High-pressure fuel injection lines (HPFILs) are precision-engineered components critical for proper engine timing, fuel metering, and combustion. The length, inner diameter, and routing (bends) of the HPFIL directly affect the pressure wave dynamics inside the line, which dictates when the fuel injector opens and closes (effective injection timing). Modern diesel engines rely on extremely precise injection timing for efficiency and emission control. Replacing a damaged line with a **factory-formed fuel injection line specifically fabricated for that cylinder (#1)** ensures that all critical parameters (length, routing, material strength, and fitting type) are maintained exactly as designed by the engine manufacturer. This is the only practice that guarantees the engine's performance specifications will be met and prevents timing imbalances between cylinders. **Explanation of why the other options are incorrect:** * **A) Custom fabricate the fuel injection line minimizing length and bends to create the shortest possible replacement fuel injection line.** This is incorrect because altering the length of the HPFIL fundamentally changes the pressure wave dynamics and effective injection timing for that cylinder. A shorter line will cause the fuel to arrive earlier than designed, leading to uneven running, potential engine damage, and poor combustion efficiency. Minimizing bends may also stress the line or make proper installation impossible. * **C) Custom fabricate the fuel injection line as close as possible to the fuel injection line being replaced in terms of bends and overall length.** While better than option A or D, custom fabrication introduces variables (inconsistent tubing material, inaccurate bending radii, imperfect length measurement, non-standard end fittings) that can compromise the line's performance or safety. HPFILs operate under extremely high pressures (often exceeding 2,000 bar or 30,000 psi), and "as close as possible" is not precise enough for the injection system's strict requirements. Factory-formed lines eliminate this risk. * **D) Replace the damaged fuel injection line with a custom fabricated line without regard to the length and configuration of the bends of the original.** This is dangerous and incorrect. Ignoring the critical parameters of length and bend configuration will guarantee incorrect injection timing and potentially lead to cylinder imbalance, severe engine vibration, reduced power, and possible catastrophic engine failure due to improper fuel atomization or hydraulic stresses.