Fuel Pump Troubles on the EMD 645 Series and Field Solutions

[MikePhua]

The EMD 645’s Legacy in Locomotive and Industrial Power
The EMD 645 series is a two-stroke diesel engine developed by Electro-Motive Division of General Motors in the mid-1960s. It succeeded the 567 series and became the backbone of North American railroads for decades. With configurations ranging from V8 to V20, the 645 was used in locomotives, marine vessels, and stationary power plants. Its name refers to the displacement per cylinder—645 cubic inches—and its design emphasized modularity, high RPM capability, and robust fuel delivery.
By the 1980s, thousands of 645 engines were in service globally. The turbocharged variants, such as the 645E3 and 645F3B, delivered up to 3,000 horsepower. Despite their durability, fuel system issues—especially involving the mechanical fuel pumps—remain a common challenge for operators and rebuilders.
Understanding the Fuel Delivery System
The EMD 645 uses a mechanically driven unit injector system. Each cylinder has its own injector, pressurized by a camshaft-driven rocker arm. Fuel is supplied from a gear-driven pump mounted on the accessory drive, which maintains consistent pressure to the injector rail.
Terminology note:

• Unit Injector: A combined injector and pump assembly that receives low-pressure fuel and generates high-pressure injection internally.
  
• Fuel Rack: A mechanical linkage that adjusts injector timing and quantity across all cylinders.
  
• Accessory Drive: A gear train that powers auxiliary components like the fuel pump, governor, and air compressor.
  

The fuel pump itself is a positive displacement gear pump, designed to deliver steady flow regardless of engine speed. It is lubricated by engine oil and includes a bypass valve to regulate pressure.
Symptoms of Fuel Pump Failure or Malfunction
Operators may encounter several signs of fuel pump trouble:

• Engine cranks but fails to start
  
• Uneven firing or misfiring under load
  
• Fuel pressure drops at higher RPMs
  
• Excessive smoke from the exhaust
  
• Fuel leaks around the pump housing or fittings
  

In one instance, a rail maintenance crew in Saskatchewan reported that their GP38-2 locomotive equipped with a 645E engine would stall intermittently during acceleration. After inspecting the fuel system, they discovered that the pump’s internal bypass valve was stuck open, causing pressure loss. Replacing the valve restored full performance.
Diagnostic Steps and Inspection Tips
To troubleshoot fuel pump issues:

• Check fuel pressure at the injector rail during cranking and idle. Normal pressure should be 35–45 PSI.
  
• Inspect the pump housing for cracks, gasket failure, or shaft seal leaks.
  
• Remove the bypass valve and test spring tension and valve movement.
  
• Verify that the accessory drive gear is intact and properly timed.
  
• Examine fuel filters and lines for blockage or air intrusion.
  

If the engine runs but lacks power, inspect the fuel rack for binding or uneven movement. A sticky rack can mimic pump failure by limiting injector stroke.
Repair Procedures and Preventive Measures
Once the fault is identified:

• Replace worn pump gears and seals using OEM or remanufactured kits
  
• Clean the bypass valve and test with a calibrated spring tester
  
• Flush the fuel system and replace filters
  
• Inspect injector timing and rack synchronization
  
• Reinstall with fresh gaskets and torque to spec
  

Preventive tips:

• Change fuel filters every 500 hours or quarterly
  
• Use fuel with proper lubricity additives to protect pump internals
  
• Monitor fuel pressure during startup and under load
  
• Keep the accessory drive lubricated and free of debris
  
• Store spare pumps in sealed containers to prevent contamination
  

One operator in Texas added a fuel pressure gauge to the cab of his switcher locomotive, allowing real-time monitoring during operation. This helped him detect a failing pump before it caused a shutdown during a yard transfer.
Design Evolution and Manufacturer Insights
The 645 series was eventually succeeded by the EMD 710, which introduced electronic fuel injection and improved emissions control. However, the 645 remains in widespread use, especially in legacy fleets and industrial installations. Rebuilders continue to support the platform with remanufactured pumps, injectors, and rack components.
Sales data from 2023 suggests that over 15,000 EMD 645 engines are still operational worldwide, with strong demand for fuel system parts and overhaul services. The modular nature of the engine allows for field repairs without full disassembly, making it a favorite among railroads and marine operators.
Conclusion
Fuel pump challenges on the EMD 645 series are common but manageable with proper diagnostics and maintenance. Whether caused by bypass valve failure, gear wear, or rack misalignment, the key is understanding the system’s mechanical logic and acting early. With the right tools and field-tested strategies, operators can keep these legendary engines running strong—delivering power where it’s needed most.