As always, read your manual first. If you're here trying to brush up on the most likely reasons that you may experience a "No start" situation, you've come to the right spot. We have listed the most common causes for a no start on a diesel engine, in order of most probable occurrence. This isn't to say that you may not have the most improbable source of a failure, but often the basics are the best place to start. First, we'll list the things to look for and then we'll explain the ones that need explanation.
We are also assuming that the motor cranks over properly.

Warning: Diesel fuel is at extremely high pressure and extreme care should be taken when dealing with the injectors, injector pump, and associated components. A fuel injector will shoot diesel fuel into your body through your skin, given the right conditions. Read all warnings and safety precautions in your manual before attempting any test procedures on a diesel engine. Wear safety goggles when dealing with high pressure diesel fuel.

Note: There are two fuel pumps on most marine diesel engines. A low pressure primary fuel pump draws fuel from the fuel tank and a high pressure fuel injector pump pressurizes the fuel lines to the injectors. Both have to be working properly

• No fuel in tank
• Closed fuel shut off valve at fuel tank
• Fuel Injector pump kill lever or solenoid
• Air in the fuel lines
• Low cranking speed
• Water in fuel
• Clogged fuel filter
• Decompression valve left open
• Manual fuel pump or primer left open or jammed
• Water in cylinders
• Low cylinder compression
• Primary fuel pump failure
• Leaking or loose injector lines
• Fuel injection pump failure

Fuel Kill Circuit

  Since the only practical way to stop a diesel engine is to "cut off" the fuel supply, almost every diesel ever manufactured uses a fuel pressure relief valve in the high pressure side of the fuel injection system.
  If this valve is stuck open or left open, or the electric solenoid that is supposed to close this valve has ceased to function, the engine will never start.  Check your owners manual for the type and function of your fuel kill system. And don't forget that a manual kill cable attached to the pressure relief valve can jam and or break and leave the valve partially open and or closed. (Also note that the number one reason for a diesel engine not to stop, is the failure of this cable and or kill solenoid)

• Operation of engine with extremely low fuel levels in the fuel tank.
• Loose or small crack in a fuel filter bleed plug washer and or filter cover
• Crack in copper fuel line at compression fitting
• Hole in primary fuel pump diaphragm

  The easiest way to check for air in your system is to carefully loosen an injector line at the injector  or the injector pump output and crank the engine, observing the fuel flow. Bubbles and or no fuel drip while cranking is not a good sign.

Careful: Do not remove the injector line from the injector or injector pump, only loosen it enough to facilitate a leak. (Always use two wrenches where the danger of twisting the injector line is imminent) Always keep a rag or pan ready to catch the dripping  fuel. Ventilate the engine room and don't allow fuel to drip on starter and other sources of ignition.

   Water in the fuel can come from several sources.

• It was pumped into the tank during refueling
• The fuel fill cap was left loose and/or the cap o-ring is cracked. 
• Excess moisture in the air with repeated atmospheric temperature changes.

Remove the fuel filters and check for water in the fuel by draining the filters into a clean clear used 2 liter soda bottle.  Let sit for awhile to see if the water settles to the bottom of the bottle.
If you have just a small amount of water; replace the filters and re-bleed the fuel system. If you have a lot of water, call a tank cleaning company to polish the fuel tank for moving forward.

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Note: This article is primarily written for traditional diesel engines that have basic mechanical operation. Newer computer controller engines with electric fuel pumps and injectors will have similar problems with poor fuel quality however, if a computer controlled engine doesn't start... check fuel quality and if it's good... call a professional.