You suspect that a diesel generator set on your offshore supply boat has a misfiring cylinder because the engine, although warm, is running roughly. The six-cylinder engine is fitted with a high-pressure distributor type pump with hydraulically operated injector nozzles. When you slacken the high-pressure fuel line at #4 fuel injector nozzle, the engine runs even rougher than before. Upon re-tightening the high-pressure fuel line fitting, the engine reverts back to the original roughness before the fitting was slackened. What does this indicate?