Diesel won't start?
  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.

 
  • 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
  • Fuel pump failure
  • Leaking or loose injector lines
  • Fuel injection pump failure

 
Note: In extremely cold weather, diesel fuel can turn to jell and of course you are not going to be able to pump jelled diesel fuel. Also note that diesel fuel will grow a fungus that will clog filters and lines and care needs to be taken to prevent this fungus before it starts to grow in your fuel system. There are numerous additives for diesel fuel that prevent and or reduce these problems. (Ask any trucker)

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)

 
  As you can tell from the list above, fuel and related issues concerning the fuel are the number one items that can cause a no start.
  Air in the fuel line can come from several sources.
  • 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 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.

 

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