Troubleshooting a No-Start Condition on a 1986 John Deere 310C Backhoe

[MikePhua]

The 310C and Its Mechanical Simplicity
The John Deere 310C was introduced in the mid-1980s as part of Deere’s long-running 310 backhoe loader series. Built with a mechanical injection system and a naturally aspirated or turbocharged diesel engine, the 310C was known for its reliability and ease of service. With over 10,000 units sold across North America, it became a staple on farms, construction sites, and municipal fleets.
Its fuel system is centered around a rotary injection pump, mechanical shutoff solenoid, and a rack-and-governor assembly that regulates fuel delivery based on throttle input. When properly maintained, the engine starts easily even in cold weather. But when neglected or left idle for months, issues like sticky linkages, weak solenoids, and air intrusion can prevent ignition.
Cranking with White Smoke but No Start
A common symptom on aging 310C units is white smoke during cranking, indicating that fuel is reaching the cylinders but combustion isn’t occurring. This can be caused by:

• Low compression due to cold temperatures or worn rings
  
• Air in the fuel system disrupting injection timing
  
• Weak starter motor causing slow cranking speed
  
• Stuck fuel rack or governor linkage preventing proper fuel delivery
  

Terminology clarification:
- White Smoke: Unburned diesel vapor, often seen during cold starts or failed ignition
- Fuel Rack: Internal linkage in the injection pump that meters fuel quantity
- Governor: A mechanical device that regulates engine speed by adjusting fuel delivery
- Shutoff Solenoid: An electrically actuated valve that cuts fuel flow when the key is turned off
In one case, the machine had a brand-new starter and fully charged batteries, yet still refused to start. The solenoid clicked when energized, and fuel flowed freely from the return line. However, the engine only ran briefly when the pump’s top cover was removed and the throttle was held wide open.
Pump Cover Behavior and Internal Linkage Diagnosis
The fact that the engine starts with the pump cover removed suggests that internal linkages—possibly the rack or governor arm—are sticking or misaligned. When the cover is off, the rack may default to full fuel delivery, allowing the engine to fire. But once the cover is reinstalled, the linkage may bind or return to a no-fuel position.
Recommended steps:

• Remove the pump cover and manually move the rack to verify free travel
  
• Inspect the governor spring and linkage for corrosion or stiffness
  
• Clean and lubricate all moving parts with diesel-compatible solvent
  
• Test the solenoid under load to confirm it holds position during cranking
  

One technician noted that a weak solenoid may click audibly but fail to hold the rack open under vibration or hydraulic pressure. Replacing it with a high-quality OEM unit resolved the issue in his case.
Cold Start Strategy and Compression Considerations
In cold climates, even a healthy 310C may struggle to start without assistance. Deere did not equip the 310C with a block heater by default, but aftermarket kits are available. Ether injection can help, but overuse risks piston damage.
Tips for cold starts:

• Use a block heater or magnetic oil pan heater overnight
  
• Crank with throttle wide open and glow plugs energized (if equipped)
  
• Avoid excessive ether—one short burst is sufficient
  
• Check cranking RPM; below 200 rpm may not generate enough compression heat
  

A mechanic in Nova Scotia shared that his 310C failed to start due to a slow cranking speed caused by a worn starter. Replacing it restored normal RPM and allowed the engine to fire even in sub-zero temperatures.
Fuel System Integrity and Air Intrusion
A constant flow from the return line suggests that fuel is circulating, but air bubbles or vapor lock may still prevent injection. If the machine has sat idle for months, seals may dry out and allow air into the system.
Solutions include:

• Bleeding the fuel system from the filter housing to the pump
  
• Replacing old rubber lines with modern ethanol-resistant hose
  
• Inspecting banjo bolts and washers for leaks
  
• Using clear tubing temporarily to monitor for air bubbles
  

If the engine runs briefly and then dies, suspect air intrusion or rack binding. If it never fires, suspect low compression or injection timing issues.
Conclusion
A 1986 John Deere 310C that cranks but won’t start is often suffering from a combination of fuel delivery issues, cold start limitations, and internal pump linkage problems. By inspecting the injection pump rack, verifying solenoid strength, and ensuring proper cranking speed, most no-start conditions can be resolved without major overhaul.
The 310C may be decades old, but its mechanical simplicity makes it a survivor. And with a bit of patience and a few turns of a wrench, it can be coaxed back to life—ready to clear snow, dig trenches, or haul gravel just like it did in its prime.