Mechanical Lift Pump Location and Function on the New Holland 555E Backhoe: Detailed Explanation, Maintenance Tips, and Practical Insights

[MikePhua]

Overview of the Mechanical Lift Pump in New Holland 555E
The New Holland 555E backhoe loader is equipped with a mechanical lift pump that plays a crucial role in supplying fuel from the tank to the fuel injection system. Unlike electric lift pumps found in some tractors and machinery, the mechanical lift pump in the 555E operates purely by mechanical means driven by the engine. Understanding its location, function, and maintenance is essential for ensuring reliable engine starting and fuel delivery performance, especially in cold or demanding environments.
Location of the Mechanical Lift Pump
According to repair manuals and user experiences, the mechanical lift pump on the New Holland 555E is typically mounted on the right side of the engine, positioned below the fuel injection pump. However, some operators have noted difficulty locating it due to engine configuration variations and emission-related modifications within different production runs of the 555E. The pump is connected mechanically via a camshaft lobe or dedicated lift arm that activates its diaphragm to create suction and pressure cycles necessary for pumping fuel.
Function and Working Principle
The mechanical lift pump functions through a diaphragm actuated by a camshaft-driven lift arm. This diaphragm movement causes alternating suction and pressure within the pump:

• Suction stroke: When the camshaft lobe presses the pump lift arm, the diaphragm moves downwards, creating suction that draws fuel from the fuel tank through the inlet line into the pump chamber.
  
• Pressure stroke: As the camshaft lobe rotates away, a spring attached to the diaphragm pushes it back upwards, compressing fuel and forcing it through the outlet side to the fuel filter and onwards to the fuel injection pump.
  

The pump contains two critical rubber check valves—one on the suction side and one on the pressure side—that open and close alternately to maintain fuel flow direction and prevent backflow, ensuring efficient fuel delivery. When these check valves fail or detach, the pump loses the ability to build adequate pressure and suction, resulting in fuel delivery problems such as hard starting or engine stalling.
Common Issues and Troubleshooting
A common issue with the mechanical lift pump is wear or failure of the internal check valves or diaphragms. Symptoms include:

• Difficulty starting the engine or requiring ether to start in cold conditions.
  
• Engine stalling or running rough due to inadequate fuel flow.
  
• Visible leaks or fuel odor near the pump area.
  

Disassembling the pump reveals rubber check valves that may become brittle or break, found as loose pieces inside the pump chamber. Also, internal filters/screens can accumulate debris, restricting fuel flow. It is recommended to:

• Inspect and clean the internal foam filter and pump chamber.
  
• Replace damaged or broken check valves.
  
• Verify the pump diaphragm's integrity for cracks or wear.
  
• Check associated banjo bolts and fuel lines for blockages or damage.
  

Maintenance and Replacement Tips
Mechanical lift pumps are generally robust but require periodic inspection and maintenance to ensure long service life. Suggested maintenance steps include:

• Removing the pump cover to inspect the diaphragm, check valves, and filter screen.
  
• Cleaning out any debris from the pump and surrounding fuel lines.
  
• Checking the seal and O-rings, replacing them if cracked or damaged.
  
• Ensuring that banjo bolts (fuel line connectors) and passages are clear from solids that can cause blockage.
  
• Reassembling carefully to maintain correct alignment of the diaphragm and camshaft lift arm engagement.
  

Replacement of the lift pump is typically straightforward and economical, with new pumps available for reasonable prices. Operators note the importance of confirming the pump is correctly timed with the camshaft lobe for effective fuel delivery.
Additional Practical Advice
During cold weather operation, such as below 20°F (-7°C), fuel delivery issues related to the lift pump can become more pronounced, as diesel fuel viscosity increases and components are more susceptible to wear. Using fuel additives or winterized diesel and ensuring fuel lines and filters are free of water and contaminants helps maintain reliable operation.
One practical tip for priming the fuel system involves loosening the banjo bolt at the pump's inlet slightly and cranking the engine to expel air bubbles until a steady stream of fuel is visible, then tightening the bolt before attempting to start the engine. This ensures the lift pump has removed air and created sufficient fuel pressure.
Case Story and Real-World Example
An operator of a New Holland 555E backhoe in a northern rural area encountered severe hard-start issues during winter. After investigation, the mechanical lift pump was found to have broken check valves inside, causing a loss of suction and fuel pressure. By replacing the pump and performing a thorough fuel system prime, they restored reliable starting and running, avoiding the frequent need for ether starts. This saved costly downtime during critical winter months and highlighted the importance of mechanical lift pump maintenance in older machinery.
Another common scenario involves clogged banjo bolt passages causing fuel starvation; cleaning or replacing these small connectors can resolve similar symptoms without full pump replacement.
Glossary of Key Terms

• Mechanical Lift Pump: A diaphragm-based fuel pump driven mechanically by the engine's camshaft, responsible for lifting fuel from the tank to the injection pump.
  
• Diaphragm: A flexible membrane inside the pump that moves up and down to create suction and pressure.
  
• Check Valve: A one-way valve that prevents fuel backflow, ensuring directional flow through the pump.
  
• Banjo Bolt: A hollow bolt used to connect fuel lines to the pump, allowing fuel flow through its hollow center and side holes.
  
• Priming: The process of removing air from the fuel system to ensure continuous fuel flow.
  
• Camshaft Lobe: A protrusion on the camshaft that actuates the pump lift arm, controlling diaphragm movement.
  

Summary and Recommendations
The mechanical lift pump on the New Holland 555E backhoe is a vital component for fuel delivery, located on the engine's right side under the injection pump, operating mechanically via a camshaft-driven diaphragm and check valves. Regular inspection and maintenance of the pump’s internal check valves, diaphragm, and fuel inlet screen are essential to prevent hard starting, fuel starvation, and engine performance issues.
Operators should:

• Ensure the pump is free from debris and the check valves are intact.
  
• Perform seasonal inspection, especially before cold weather.
  
• Use proper priming techniques to eliminate air pockets.
  
• Replace worn or damaged lift pumps promptly.
  
• Maintain fuel quality and keep filters clean to aid pump function.
  

By following these practices and addressing common problems proactively, New Holland 555E users can maintain reliable fuel system operation, reduce downtime, and extend the life of their backhoe loader in demanding working conditions.
This knowledge is applicable not only to New Holland 555E but to similar diesel engines using mechanical lift pumps, providing practical wisdom for heavy equipment operators worldwide.