Troubleshooting Starting Failures in the Cummins 6T590: Fuel Contamination, Injection Pressure, and Field Recovery

[MikePhua]

Engine Overview and Context
The Cummins 6T590 is a turbocharged inline-six diesel engine commonly found in heavy equipment like the Case 855D track loader. Known for its durability and torque output, the 6T590 relies on a mechanical Bosch inline injection pump and electric fuel shutoff solenoid. When starting issues arise—especially after a rebuild or swap—technicians must consider fuel delivery, air intrusion, and contamination as primary suspects.
In one case, a freshly rebuilt 6T590 ran flawlessly until it abruptly shut down, as if the electric fuel shutoff had been triggered. Despite fuel reaching the pump and injectors, the engine refused to start, prompting a deep dive into the fuel system.
Terminology Explained
- Bosch Inline Injection Pump: A mechanical pump that meters and pressurizes fuel to each injector
- Fuel Shutoff Solenoid: An electrically actuated valve that cuts fuel flow when de-energized
- Bleeding Injectors: The process of removing air from fuel lines and injector bodies to restore pressure
- Fuel/Water Separator: A filter that removes water from diesel fuel to prevent injector damage
Initial Diagnosis and Observations
The technician confirmed:

• Fuel was present at the injector pump inlet
  
• The shutoff solenoid was removed and tested
  
• Compression was strong, ruling out mechanical failure
  
• Ether was considered but not used due to safety concerns
  

Suspecting a sheared pin on the pump drive gear, the team inspected the gear through the access port while cranking. However, the gear rotated normally, eliminating mechanical failure as the cause.
Discovery of Water Contamination
After bleeding the injectors, the engine briefly started but stalled again on an incline. This behavior—running fine on level ground but starving on a grade—suggested water contamination or air intrusion. Upon draining the fuel tank and separator, water was found in the system. The technician suspected vandalism, as the machine had been parked unattended.
Field Story: Fuel Sabotage and Recovery
In a similar case in rural Texas, a contractor’s excavator began stalling intermittently. After weeks of troubleshooting, they discovered sugar had been poured into the fuel tank—a deliberate act of sabotage. The repair involved draining the tank, replacing filters, and flushing the entire fuel system. Since then, they’ve installed locking fuel caps on all machines.
Additional Parameters and Suggestions

• Fuel pressure at injector pump inlet: ~5–7 psi
  
• Injection pressure at nozzle: ~3,000–5,000 psi
  
• Recommended fuel: Ultra Low Sulfur Diesel (ULSD)
  
• Filter change interval: Every 250–500 hours
  
• Shutoff solenoid voltage: 12V DC
  

Recommended Diagnostic Steps

1. Check Fuel Quality
   • Drain tank and inspect for water or debris
     
   • Replace fuel with fresh, filtered diesel
     
   • Use biocide if microbial growth is suspected
     
2. Bleed the System Thoroughly
   • Open injector lines and crank engine until fuel spurts evenly
     
   • Tighten lines and attempt restart
     
   • Repeat if engine stalls again
     
3. Inspect Fuel Shutoff Solenoid
   • Remove solenoid and test for actuation
     
   • Replace if coil is weak or plunger sticks
     
   • Ensure proper grounding and voltage supply
     
4. Test Injection Pump Output
   

• Use a pop tester to verify injector spray pattern
  
• Check for consistent pressure across all cylinders
  
• Rebuild pump if output is weak or uneven
  

Preventive Maintenance Tips

• Lock fuel caps to prevent tampering
  
• Drain water separator weekly in humid climates
  
• Use fuel additives to prevent microbial growth
  
• Train operators to recognize early signs of fuel starvation
  
• Keep spare filters and hand pump onboard for field bleeding
  

Conclusion: Fuel System Integrity Is Everything
The Cummins 6T590 is a reliable engine, but its mechanical fuel system is vulnerable to contamination and sabotage. When starting issues arise, especially after a rebuild, technicians must methodically inspect every component—from tank to injector. In this case, water in the fuel caused intermittent stalling and hard starts, resolved only by a full system flush. The lesson is clear: protect your fuel, bleed your lines, and never underestimate the damage a few ounces of water can do.