Case 580K CAV Injection Pump Fuel Return Troubleshooting

[MikePhua]

The Case 580K and Its Fuel System Design
The Case 580K backhoe loader was introduced in the late 1980s as part of Case Corporation’s evolution of the 580 series, which had already become a staple in construction and utility work. The 580K featured mechanical simplicity, a robust hydraulic system, and a reliable diesel engine—often paired with a CAV rotary injection pump. Case, founded in 1842, had by this time become a global leader in agricultural and construction machinery, and the 580K contributed to tens of thousands of units sold across North America and Europe.
The CAV injection pump used on the 580K is a rotary-type pump with an internal fuel solenoid and a return circuit that routes excess fuel back to the tank. This system is designed to maintain consistent fuel pressure, purge air, and prevent vapor lock during operation.
Symptoms of Hot Start Failure
A recurring issue with the 580K’s CAV pump is difficulty restarting the engine shortly after shutdown. Cold starts are typically reliable, but when the machine is turned off and restarted within minutes, the fuel solenoid fails to engage properly. Operators often resort to manually relieving pressure by opening the water separator drain, which allows the solenoid plunger to drop and fuel to flow.
This behavior suggests that residual pressure in the fuel line between the lift pump and injection pump is preventing the solenoid from actuating. While the solenoid may test fine on the bench, in-field conditions reveal a pressure-related fault.
Understanding the Fuel Return Circuit
The fuel return system includes:

• A top cover outlet on the injection pump
  
• A T-fitting that merges return flow from the injectors
  
• A short rubber hose leading to a check valve mounted in the frame
  
• A final line returning fuel to the tank
  

The check valve, often identified as part number A177556, is designed to prevent backflow and maintain prime. However, if this valve sticks or becomes blocked, pressure may build in the pump housing, interfering with solenoid operation.
Terminology Clarification

• Fuel Solenoid: An electrically actuated valve that controls fuel flow into the injection pump.
  
• Check Valve: A one-way valve that allows fuel to flow toward the tank but prevents reverse flow.
  
• Lift Pump: A mechanical pump that supplies fuel from the tank to the injection pump.
  
• Overflow Pipe: A return line that carries excess fuel back to the tank.
  

Diagnostic and Repair Strategy
To resolve the issue:

• Inspect the return line from the pump to the tank for blockages or collapsed hoses.
  
• Remove the return fitting from the pump and check for a floating check ball. If present, consider knocking it out to prevent sticking.
  
• Replace the anti-drain check valve if it shows signs of internal restriction.
  
• Verify that the lift pump is functioning and not introducing air into the system.
  
• Use a line wrench to loosen fittings and avoid damaging soft metal connectors.
  

In one case, a contractor in South Carolina discovered that the check ball inside the return fitting had become lodged in the housing, creating excessive pressure. After removing the ball and flushing the return line, the machine restarted reliably under all conditions.
Alternative Solenoid Bypass
For field testing, operators can bypass the solenoid by removing its internal spring and plunger (if the unit is serviceable) and reinstalling the body. The engine can then be shut down manually using the mechanical lever on the front of the pump. This method confirms whether the issue is electrical or pressure-related.
A Story from the Field
In British Columbia, a backhoe operator experienced intermittent hot start failures during spring orchard prep. After replacing the solenoid twice and checking wiring, he discovered that the return line had a kink near the frame-mounted check valve. Once replaced, the machine started flawlessly—even after short shutdowns. Ironically, the issue had cost him half a day of troubleshooting and a spilled tank of diesel.
Preventive Measures and Recommendations

• Replace rubber return hoses every 5 years to prevent internal collapse.
  
• Clean or replace check valves during major service intervals.
  
• Use OEM solenoids with sealed boots to prevent moisture intrusion.
  
• Label fuel lines and fittings to simplify future diagnostics.
  
• Keep a spare solenoid and check valve in the field kit.
  

Conclusion
Hot start issues on the Case 580K with a CAV injection pump are often caused by residual fuel pressure and return line restrictions. By inspecting the check valve, return fittings, and solenoid operation, operators can restore reliable performance and avoid unnecessary downtime. The simplicity of the system makes it field-serviceable, but attention to detail is essential for long-term reliability.