Cummins Incorporated, one of the world's largest manufacturers of diesel engines, produces many types of diesel engines for a wide variety of uses. There are many details involved in troubleshooting a Cummins motor, but learning a few fundamentals is very helpful. For instance, if the engine is sluggish, check the fuel and air systems, and if the engine won't start, inspect the battery and starter circuit.
Check fuel quality first, since all diesel engines are subject to fuel system problems. Contaminated fuel can slow or stop the motor. Was your truck running fine right up until the last time you fuelled it? If so, you should suspect fuel contamination.
Add No. 1 diesel fuel or an anti-gel additive if the engine is losing power in extremely cold weather. Regular diesel fuel tends to gel at temperatures below -12.2 degrees C. and can make the engine sluggish and hard to start.
Check the injection system. The injectors must be clean in order to supply each cylinder with the correct amount of fuel. Visually inspect the individual injector lines for damage and check the tightness of each injector at the cylinder head.
Check the fuel pump if your truck starts normally, but has low power. Look for loose wires going to it. If it the cause is not an external wire or blown fuse, you will need to have the fuel pump output tested by a professional.
Check the air delivery system. Cummins diesels must have a good supply of air at all times. If the engine has had low power over a period of time, check the air intake system and filter for excessive dirt or debris.
Check the turbocharger while the engine is running. If you hear sporadic hissing or metallic noises coming from the turbocharger and also note a corresponding drop in engine power, it is likely the turbocharger is failing.
Check the battery if your diesel won't start If don't hear the starter cranking when you turn the ignition key to "Start," or hear just clicking sounds, you probably have a dead battery.
Electronic engine management systems are now standard on most Cummins engines. However, only a person who has the proper equipment and training should use these systems for troubleshooting.