Diagnosing Intermittent Starting Issues on the Case 850H Dozer

[MikePhua]

The Case 850H and Its Engine Platform
The Case 850H crawler dozer is part of the long-standing 850 series developed by Case Construction Equipment, a brand under CNH Industrial. Introduced in the early 2000s, the 850H was designed for mid-size grading, site preparation, and forestry work. It features a hydrostatic transmission, advanced blade control, and a Cummins 6BT 5.9L diesel engine paired with a Bosch inline injection pump. With an operating weight of around 19,000 lbs and a net horsepower rating near 95 hp, the 850H became a popular choice for contractors and municipalities seeking a balance of power and maneuverability.
The 6BT engine, known for its mechanical simplicity and durability, has been used in a wide range of equipment and vehicles, including Dodge Ram trucks, agricultural tractors, and generators. Its Bosch P7100 injection pump is a mechanical workhorse, but like any fuel system, it relies on precise timing, clean fuel delivery, and functional solenoids to start and stop reliably.
Terminology Annotation

• Fuel Shutoff Solenoid: An electrically actuated valve that controls fuel flow to the injection pump, enabling engine start and stop.
  
• Primer Button: A manual pump used to pressurize the fuel system before starting, especially after air intrusion or filter changes.
  
• Injector Seal: An O-ring or gasket that prevents fuel from leaking into the combustion chamber or draining from the injector body.
  
• Run Coil and Start Coil: Dual windings in some solenoids; the start coil initiates movement, while the run coil holds the solenoid in position.
  

Symptoms of Starting and Shutdown Irregularities
Operators have reported that the Case 850H occasionally fails to start on the first attempt, requiring multiple cranks or manual priming. Once started, the engine runs smoothly and restarts easily throughout the day. However, when shutting down, the engine sometimes continues running for several seconds after the key is turned off.
These symptoms suggest a combination of fuel delivery delay and solenoid malfunction. The delayed shutdown points to a sticky or weak fuel shutoff solenoid, while the hard cold start may indicate air intrusion or fuel drain-back caused by compromised injector seals or a clogged tank vent.
Diagnostic Path and Component Checks
To isolate the issue, technicians should follow a structured approach:

• Inspect the fuel shutoff solenoid for proper movement. Remove it from the pump and apply power to verify actuation. Ensure both the start and run coils are functioning if dual-coil design is used.
  
• Check for voltage at the solenoid terminals with the key on and off. Confirm that power is cut when the key is turned off.
  
• Examine the fuel tank vent for blockage. A clogged vent can create vacuum resistance, preventing fuel from flowing freely.
  
• Drain the fuel/water separator and inspect for contamination or emulsified diesel.
  
• Test injector seals for leakage. A failed lower O-ring can allow fuel to drain into the cylinder, causing extended run-on and hard starting due to fuel displacement.
  

A Story from the Field
In 2013, a dozer operator in Tennessee experienced similar issues with his 850H. After replacing the solenoid and confirming voltage, the machine still ran for a few seconds after shutdown. A retired technician suggested inspecting the injector seals. Upon removal, the lower O-rings were found brittle and cracked. Replacing them resolved both the delayed shutdown and the morning hard-start condition. The operator also installed a transparent fuel line to monitor air bubbles, which helped confirm the system was sealed.
Component Compatibility and Cross-Reference Notes
The Bosch P7100 pump used on the 6BT engine shares design features with pumps found on Dodge Ram trucks from 1994–1998. These pumps use a dual-coil solenoid, and aftermarket replacements are widely available. However, not all solenoids are created equal—some budget units lack the torque to fully actuate the fuel rack, leading to intermittent shutdowns.
When sourcing parts:

• Confirm solenoid resistance (typically 10–15 ohms per coil)
  
• Use Viton or fluorocarbon injector seals for heat resistance
  
• Replace fuel filters with OEM-rated micron levels (usually 10–15 micron primary)
  
• Avoid mixing fuel additives unless approved for diesel injection systems
  

Preventative Maintenance Recommendations
To prevent future starting issues:

• Replace injector seals every 2,000 hours or during major service
  
• Clean or replace the fuel tank vent annually
  
• Test solenoid function during each oil change
  
• Prime the system after filter replacement or extended storage
  
• Use diesel with low water content and store fuel in sealed containers
  

Industry Trends and Electronic Integration
Modern dozers now feature electronic fuel control modules and diagnostic interfaces. In 2024, Case introduced a smart solenoid system with integrated feedback sensors that confirm actuation and report faults to the operator display. While the 850H predates these systems, retrofitting a pressure sensor or installing a manual override switch can improve reliability.
Aftermarket kits are available to convert mechanical solenoids to electronic pulse-actuated units, reducing wear and improving response time. These upgrades are especially useful in cold climates or high-cycle applications.
Conclusion
Starting and shutdown issues on the Case 850H often stem from fuel system inconsistencies, particularly solenoid wear and injector seal failure. By methodically inspecting electrical connections, fuel flow, and sealing components, operators can restore reliable performance. With proper maintenance and attention to detail, the 850H remains a dependable machine capable of tackling tough terrain and long hours with confidence.