Question 8 OSE01 - Chief Engineer - OSV

The Correct Answer is A **Why Option A is Correct:** Option A describes a classic high-pressure injection system common on auxiliary diesel engines (like those used on offshore supply vessels) where the high pressure is generated by a multi-plunger pump (such as an inline pump or a pump-line-nozzle system). In this setup: 1. The high-pressure fuel is delivered from the pump element to the separate injector nozzle via a rigid, external high-pressure steel tube (the fuel injection line). 2. The diagnostic technique of "loosening the high-pressure fuel injection line fitting at the injector nozzle" works precisely because it relieves the pressure necessary for injection, causing the fuel to leak out harmlessly instead of being sprayed into the combustion chamber. This effectively disables the cylinder, allowing the engineer to determine if the misfire changes when that cylinder is cut out. This technique is only feasible when an accessible high-pressure line exists between the pump and the nozzle. **Why Options B, C, and D are Incorrect:** * **B) Electronically operated unit injectors...** This system integrates the pump and nozzle into a single unit mounted directly in the cylinder head (EUI). There is no external high-pressure fuel line to loosen. Troubleshooting for misfires in these systems involves electronic disabling (unplugging the injector solenoid) or using diagnostic software, not physically loosening a fitting. * **C) Mechanically operated injection nozzles where each nozzle is supplied by a separately housed pressure/time (PT) metering pump.** The Cummins PT system is unique. While it uses external lines, it relies on low pressure (metered pressure) being supplied to unit injectors (which develop the necessary injection pressure internally). The injection nozzle itself is part of the unit injector assembly, and the primary high pressure is not contained in an external line that can be loosened for cut-out testing in the traditional manner described. * **D) Mechanically operated unit injectors...** Similar to option B, a mechanical unit injector (MUI) integrates the pump plunger and the nozzle into one self-contained unit. Since the high pressure is developed and contained entirely within the unit injector body, there is no external high-pressure fuel injection line to loosen for troubleshooting purposes.