Diesel Small Engine will not run/stops

The information contained in our websites is designed as a guide only, for assisting Repair Professionals. By using our information you are agreeing to our T&Cs.

If your Engine will turn over with no obstruction, besides how hard it is to turn through the compression stroke, please follow these tips. If there is an obstruction and the engine will not turn over, please contact us by submitting a ticket below.


1. First be sure you have enough oil in your equipment. If your oil is filled to the correct level and it still won’t start, or shuts itself down after a short time, disconnect the single wire from the oil sensor (usually found just above the oil filter) and try running the unit. If the engine starts with this wire removed, it means that the Oil Sensor needs replacing.

Do not run the engine for prolonged periods of time without the Oil Sensor attached. This device protects your engine from catastrophic failure, in the event the oil gets low or the pressure drops. This inexpensive part could save your engine from a very expensive repair!

2. Service your equipment. This fixes most running problems as you should service your Small Engine Equipment as instructed in your operating manual. Change all of the fuel filters, the oil filter, and the oil and inspect the air filter closely. The foam of the air filter has a tendency to break up and get pulled into the head. To give you an idea of how important regular servicing is, the standard is to service every year, or every 500 hours, whichever comes first. Full Service Kits are available for most Small Engine equipment.

3. Replace fuel with fresh fuel and check the tank does not contain any debris or rust, as this will eventually enter the cylinder head and begin to cause damage. Drain some fuel into a glass and inspect it for particles and/or (a small layer of) water. Replace rusted Fuel Tanks as soon as possible as the contaminants will damage your engine. Replace all the fuel (and flush the tank by swilling with a small quantity of fresh diesel) if you find water or contaminates.

4. Check if there is an airlock in the diesel system.

This can happen if your equipment runs out of diesel while it is running, or after a repair, when air could have entered the system.

  • Start by removing the Rubber Fuel Line from before the injector pump on the front of the engine.
  • Turn on the fuel Petcock and make sure the fuel is free-flowing. If the fuel is not free-flowing, check the fuel is definitely turned on, also check if any filters are clogged and need to be replaced. Reattach this line to the Pump.
  • Next, undo the metal fuel line from after the Pump and turn over the Engine until diesel flows from the Pump.
  • Now reattach the Metal Fuel Line to the Pump, clean up any spilled diesel (spilled fuel is a fire hazard!) and manually turn over the Engine.
  • Now, undo the Metal Fuel Line from the Injector end and turn over the Engine. Once the fuel is free-flowing from the Metal Fuel Line, reattach the Metal Fuel Line to the Injector.
  • This should ensure there is no longer an airlock in the system.

If you still cannot start the Engine:

  • Detach the Injector pipe from the Injector, remove the Injector from the cylinder head and now reattach the Injector to the Injector pipe. Point the Injector upwards and hold a clear glass over it. Turn over the Engine and hopefully watch the fuel spray into the glass. The Injector should release diesel from the 4 tiny holes with a strong jet. If the Injector does not spray from all 4 holes you will need to replace the Injector Nozzle.
  • If the spray into the glass is weak, then you will need to replace the Injector Pump.

5. If you had removed the Injector Pump previously, and the above does not fix the problem, it may be the Injector Pump Timing Shim(s) are missing or the Yoke (from the governor linkage inside the engine) is not engaging with the Injector Pump. You can check the Yoke by removing the inspection plate on the front of the Pump and moving the Run/Stop lever. It should move the Yoke left and right, and in between the Yoke you should see the “Pump Pin” move too. If not, you will need to reinstall the Pump so this Pin is sitting between the Yoke. Please let us know if you need help with this.

Ask Roary

Did this fix the issue?

Spanner Driver Answer

Yes, thanks! Help me find the parts.

Spanner Driver Answer

No, I need more help.