This injector washer seals the interface between the injector body and the cylinder head in the fuel system. It maintains the correct injection pressure by preventing compression leakage past the injector seat. A worn or crushed washer causes hard starting, misfire, or reduced engine power. The washer is manufactured to the original thickness specification, which the injector clamping force relies on for proper sealing. Replace the washer whenever an injector is removed; do not reuse the old one.