Why the John Deere 450B Won’t Start Despite Fuel at the Pump

[MikePhua]

The issue is most likely a blocked or failed injection pump. Although fuel reaches the pump, none is delivered to the injectors. This points to internal pump failure, clogged screens, or a compromised drive mechanism.
A Classic Crawler with Mechanical Simplicity
The John Deere 450B crawler dozer, produced in the early 1970s, was built for rugged earthmoving with a straightforward mechanical diesel engine. Its popularity stemmed from reliability, ease of maintenance, and parts availability. Powered by a naturally aspirated 3-cylinder diesel, the 450B used a mechanical fuel injection system with a rotary pump—typically a Roosa Master or similar design.
Terminology Clarification

• Injection Pump: A mechanical device that meters and pressurizes fuel for delivery to each injector.
  
• Fuel Shutoff Solenoid: An electrically actuated valve that stops fuel flow when the key is turned off.
  
• Timing Window: A small access port on the pump used to verify internal gear rotation and timing marks.
  
• Return Line: A low-pressure line that allows excess fuel to exit the pump and return to the tank.
  

Failure Sequence and Observations
The machine initially showed signs of fuel starvation—revving erratically before stalling. After replacing sludge-filled filters and bleeding the system, it restarted and ran for an hour before repeating the failure. This time, cleaning and bleeding had no effect. Fuel was confirmed at the pump inlet, but none reached the injectors.
This behavior suggests:

• Internal blockage: Sludge or debris may have clogged the fine mesh screen inside the pump inlet or return circuit.
  
• Drive failure: Some pumps use a fiber drive plate that can shear silently, leaving the pump body intact but non-functional.
  
• Air lock: Dry injector lines take time to refill, especially if the pump isn’t generating pressure.
  
• Solenoid malfunction: If the shutoff solenoid fails in the closed position, fuel won’t reach the injectors even if the pump is intact.
  

Recommended Diagnostic Steps

• Crack injector line nuts and crank the engine. If no fuel spurts out, the pump isn’t delivering.
  
• Remove the timing window cover and rotate the engine. Confirm that internal pump components are moving.
  
• Check the fuel return line for blockage. A plugged return can cause internal pressure buildup and prevent delivery.
  
• Inspect the solenoid for proper operation. Listen for a click when the key is turned on, and verify voltage at the terminal.
  
• Rod out the tank vent to ensure fuel flow isn’t restricted by vacuum lock.
  

Repair and Replacement Advice
If the pump is confirmed faulty:

• Remove and send it to a diesel injection specialist for rebuild.
  
• Replace all filters and flush lines to prevent recontamination.
  
• Consider replacing the fuel tank or installing a pre-filter if sludge is persistent.
  
• Use clean diesel and add biocide if microbial growth is suspected.
  

Field Anecdote
One operator in Queensland shared that his 450B failed similarly. After cracking injector lines and seeing no fuel, he discovered the pump’s fiber drive had disintegrated. A rebuilt pump restored full function, and the machine ran reliably for years afterward.
Conclusion
When a John Deere 450B won’t fire despite fuel at the pump, the problem lies within the injection system—most likely a blocked or failed pump. By checking drive rotation, solenoid function, and return flow, operators can isolate the issue and restore this classic crawler to service. With proper care, the 450B remains a dependable workhorse decades after its debut.