Case 750K Bulldozer Won’t Shut Down Properly

[MikePhua]

Overview of the Case 750K Series 3 Bulldozer
The Case 750K Series 3 is a mid-sized crawler dozer designed for grading, site preparation, and utility work. Manufactured by Case Construction Equipment, a division of CNH Industrial, the 750K features a turbocharged diesel engine, hydrostatic drive, and electronically controlled fuel systems. With an operating weight of approximately 36,000 lbs and a net horsepower rating of 160 hp, the machine balances power and maneuverability. Case introduced the Series 3 with improved cab ergonomics, diagnostics, and emissions compliance, making it a popular choice for contractors and municipalities.
Symptoms of Shutdown Failure
A recurring issue with some 750K units is that the engine continues to run after the ignition key is turned off. Initially intermittent, the problem may worsen over time, requiring manual intervention—such as tapping the injection pump or manipulating throttle input—to stop the engine. In one instance, the machine would shut off when cold but refused to do so once warmed up, suggesting a thermal or electrical component failure.
Understanding the Fuel Shutoff System
The 750K uses a VE-type rotary injection pump, commonly manufactured by Bosch or Stanadyne. These pumps include an electric fuel shutoff solenoid, which receives voltage from the ignition circuit. When energized, the solenoid retracts a plunger, allowing fuel to flow. When de-energized, the plunger extends and blocks fuel delivery, stopping the engine.
Key components include:

• Shutoff solenoid: Mounted on the top cover of the injection pump, typically with a single wire and a ground strap.
  
• Cold start solenoid: Located nearby, this unit advances timing during cold starts and can interfere with shutdown if malfunctioning.
  
• Return line check valve: Contains a glass ball that regulates fuel return flow. If damaged or removed, it can mask deeper pump issues.
  

Diagnostic Steps and Observations
Operators have reported the following findings:

• Voltage at the solenoid remains present even after key-off, suggesting a wiring or relay fault.
  
• Disconnecting the solenoid wire sometimes fails to stop the engine, indicating internal pump damage.
  
• Tapping the pump near the return line causes shutdown, pointing to mechanical interference.
  
• Removing the solenoid reveals a plunger and spring—if these are missing or jammed, shutdown will fail.
  

One technician noted that the cold start solenoid can explode internally, preventing the shutoff plunger from extending. Another observed that the solenoid connector was corroded, reducing current flow and causing erratic behavior.
Recommended Solutions
To resolve the issue:

• Clean and inspect solenoid wiring, especially connectors and ground points.
  
• Test solenoid function using a battery charger: apply 12V to the terminal and ground the body. A working solenoid will snap the plunger upward.
  
• Remove and inspect the solenoid: check for debris, wear, or missing components. Be cautious—plungers and springs may eject under tension.
  
• Check for manual override lever: some VE pumps include a manual shutoff, though not all models have it.
  
• Inspect the return line check valve: if the glass ball is missing, fuel may bypass the shutoff mechanism.
  

If the solenoid is confirmed faulty, replacement costs range from $120 to $180, depending on supplier. However, if internal pump damage is suspected—such as weight retainer failure or metal contamination—full pump rebuild may be necessary.
Access Challenges and Tooling Advice
Accessing the solenoid can be difficult due to its location beneath injector lines and brackets. Recommended steps include:

• Remove throttle linkage and dipstick tube for clearance.
  
• Use a 15/16-inch distributor wrench, ground down for clearance.
  
• Avoid removing the injection pump unless absolutely necessary.
  

One operator fabricated a custom wrench to reach the solenoid without disturbing the pump, saving hours of labor.
Conclusion
The Case 750K’s refusal to shut down is typically caused by electrical faults, solenoid failure, or internal pump wear. Systematic diagnosis—starting with voltage checks, connector cleaning, and solenoid testing—can pinpoint the issue. With proper tools and careful inspection, most shutdown problems can be resolved without major disassembly. The 750K remains a reliable workhorse, and addressing this issue ensures safe and predictable operation.