Question 63 3AE01 - Third Assistant Engineer

The Correct Answer is C **Why option C ("filter the fuel") is correct:** In illustrations pertaining to common mechanical fuel injection systems (such as those used in diesel engines, often depicting unit injectors or similar components), the component designated as a filter (or screen) is placed immediately upstream of the finely machined parts (like the plunger and barrel assembly or the needle valve). Piece #38 is typically a small, cylindrical screen or filter element integrated into the injector body or inlet fitting. Its primary function is to trap very small contaminants or debris immediately before the fuel enters the high-pressure pumping and injection mechanism, protecting the precision components (which operate with extremely tight tolerances) from damage or sticking. Therefore, its purpose is to filter the fuel. **Why the other options are incorrect:** * **A) adjust the fuel rack spring tension:** Fuel rack spring tension adjustment (which controls idle speed or maximum engine speed/fuel delivery) is handled by external linkage adjustments or internal mechanisms within the governor or fuel pump, not usually by an internal component like a small screen (#38) situated at the fuel inlet of the injector. * **B) maintain fuel pressure at a preset level:** Maintaining a steady, preset supply pressure (transfer pressure) is the job of the transfer or lift pump and often a separate pressure regulating valve located on the engine or pump housing, not a simple filter screen (#38) inside the injector. * **D) relieve excess fuel pressure to the suction side of the pump:** Relieving excess fuel pressure is the function of a relief valve or pressure regulator (often called a return check valve or bypass valve), which is usually located on the fuel header or return line. While injectors do have a return path for leakage fuel, the component labeled #38 is specifically positioned to filter the incoming fuel, not regulate system pressure or return flow.