Cleanliness is probably one of the greatest aids in detecting leakage. When an engine is secured because of
trouble, the procedure for repairing the casualty follows an established pattern if the trouble has been
diagnosed. If the location of the trouble is not known, it must be found. To inspect every part of an engine,
whenever a trouble occurs, would be an almost endless task. The cause of a trouble can be found much more
quickly if a systematic and logical method of inspection is followed. Generally speaking, a well-trained
troubleshooter can isolate a trouble by identifying it with one of the engine systems. Once the trouble has been
associated with a particular system, the next step is to trace out the system until the cause of the trouble is
found. Troubles generally originate in only one system. However, remember that troubles in one system may
cause damage to another system or to engine components. When a casualty involves more than one system of
the engine, each system must be traced separately and corrections made as necessary. The troubleshooter must
know the construction, function, and operation of various systems as well as the parts of each system for a
specific engine before he/she can satisfactorily locate and remedy troubles. Many troubles may affect the
operation of a diesel engine. However, satisfactory performance depends primarily on the presence of
sufficiently high compression pressure and injection of the right amount of fuel at the proper time. Proper
compression depends basically on the pistons, piston rings, and valve gear, while the right amount of fuel
depends on the fuel injectors actuating mechanism. Such troubles as lack of engine power, unusual or erratic
operation, and excessive vibration may be caused by either insufficient compression or faulty injector action.