Troubleshooting a Denso CO2310 Injection Pump That Delivers No Fuel

[MikePhua]

Understanding the Denso CO2310 Pump System
The Denso CO2310 is a mechanical injection pump widely used on diesel engines in heavy equipment and tractors. Its role is to draw fuel from the tank and deliver it under high pressure to engine injectors. If the pump suddenly delivers no fuel—even though the lift pump and fuel lines are intact—it signals an internal fault or blockage within the pump system itself.

Symptoms of “No Fuel Out” from the Injection Pump

• Fuel pressure and flow exist up to the pump inlet, but nothing exits the pump.
  
• The engine cranks but fails to fire.
  
• No fuel appears at injector lines even when the engine is cranked with throttle wide open.
  
• Fuel shut-off solenoid does not click or functions improperly.
  
• Pump may be seized or unresponsive.
  

Possible Causes Behind the Pump Failing to Deliver Fuel

1. Fuel Shut‑Off Solenoid Malfunction
   The solenoid may stay in the closed position internally, even though the key is on. This prevents fuel entering the pumping chamber. Disconnection or replacement is often necessary to test function.
   
2. Internal Seizure or Sticking Mechanism
   The mechanical governor, rack, or internal plungers can seize due to corrosion, lack of lubrication, or mechanical damage, preventing the fuel chamber from filling or delivering.
   
3. Air or Contamination Lock Inside the Pump
   Air pockets or debris may block fuel flow inside the pump. Without discharge at the output lines, this could indicate blockage or internal seal failure.
   

Diagnostic Steps to Identify the Cause

• Verify Fuel Supply Up to Pump: Confirm the lift pump delivers fuel under constant pressure.
  
• Check the Shut‑Off Solenoid: Listen for the solenoid clicking at key‑on. Disconnect it and try cranking to see if fuel flows out.
  
• Test for Internal Movement: Remove any access cover (such as throttle plate); manually move the control rack to see if it’s binding or seized.
  
• Bleed or Prime System: Use primer pump or cranking with fuel inlet open until fuel is observed, then secure fittings and test again.
  
• Inspect Pump Internals: If rack or plungers fail to move, the pump may require disassembly or replacement.
  

Maintenance Practices to Prevent Future No‑Fuel Conditions

• Keep fuel clean and free from sediment—use quality filters and change them regularly.
  
• Never run the tank dry—this can introduce air, cause cavitation, and reduce lubrication inside the pump.
  
• Use fuel system lubricants or additives compatible with diesel to prevent internal sticking or galling, especially in older mechanical pumps.
  

Key Terminology Explained

• Shut‑Off Solenoid: Electrically operated valve that allows or blocks fuel flow into the pump.
  
• Governor/Rack Mechanism: Controls fuel delivery and engine speed; can seize or bind.
  
• Primer Pump: Manual or electric pump used to purge air and prime fuel system.
  
• Cavitation: Condition where low pressure causes vapor bubbles, damaging pump internals.
  

Example Case: Unexpected Fuel Loss
An operator on a Ditch Witch 2310 trencher reported that, although fuel reached the pump, nothing was delivered—even with throttle wide open and lift pump working. After bypassing a suspect shut‑off solenoid and cranking the system until fuel reached injector lines, the machine fired up. The diagnosis: a solenoid stuck in the closed position prevented any fuel from entering the injection pump.

Summary Checklist

• Verify fuel reaching pump inlet.
  
• Listen for solenoid click and test by disconnecting it.
  
• Manually move rack linkage to confirm internal movement.
  
• Prime system fully before attempting start.
  
• Consider internal seizure or blockage if pump does not deliver.
  

Conclusion
When a Denso CO2310 injection pump fails to deliver fuel despite supply to the inlet, the issue invariably lies within the pump itself: either a stuck shut‑off solenoid, seized mechanical internals, or blockages. By systematically checking fuel supply, solenoid function, and internal linkage movement, technicians can accurately diagnose the root cause. Proper fuel hygiene, avoidance of air intrusion, and preventive lubrication help ensure long-term reliability of these critical fuel injection systems.