Case 1835C Injection Pump Malfunction: A Comprehensive Investigation and Practical Guide

[MikePhua]

Overview of the Fuel Delivery Failure on the Case 1835C
The Case 1835C skid steer with TMD20 diesel engine may experience a serious fault following engine rebuilds or internal failures: the injection pump may appear operational, yet no fuel reaches the injectors, resulting in no power or intermittent operation. This article dives into diagnostic protocols, components, and real-world fixes based on user reports and technical insight.
Fuel Supply and Return Circuit Basics
Understanding the system hydraulically:

• Fuel supply enters the injection pump via a mechanical or electric lift pump.
  
• Fuel return lines from injectors and pump overflow route back to the tank, often through a Tee fitting at the pump cover.
  
• Shut-off solenoid controls fuel flow; typically located on the injector pump top cover.
  

Issues can arise if:

• Supply is good but fuel stalls at the pump inlet.
  
• Return passages are restricted, creating pressure that prevents fuel delivery to injectors.
  
• The metering valve (MV) or internal pump governor becomes stuck.
  

Diagnosis Checklist

• Ensure fuel inlet at pump has steady flow—disconnecting feed at injector pumps can verify.
  
• Loosen injector outlet lines at the injectors a few turns to test if fuel flows while cranking at high throttle—indicates supply & pump activity .
  
• Remove all return line fittings at pump cover and run engine with throttle wide open, observing any fuel exiting the holes .
  
• If fuel appears and runs well, retain throttle then reinstall return fittings slowly—if engine stalls again, a clog in return side is likely.
  

Metering Valve (MV) and Solenoid Behavior

• The MV sits under the top cover; its free movement is essential. If the throttle linkage or governor spring binds, fuel delivery is halted .
  
• The fuel shut-off solenoid coil must receive full 12 V with engine running; intermittent or weak voltage may cause pump shutoff mid-operation .
  

Real‑World Cases and Resolution
A user who rebuilt the engine noted the injection pump was previously functional but failed after the rebuild. Fuel slowly leaked from the pump inlet but nothing reached the injectors despite hours of cranking with glow plugs out. After removing and inspecting the top cover they discovered:

• The Tee fitting was clear, but the port beneath was clogged from debris.
  
• Restoring flow by cleaning that hole allowed the engine to run consistently for several minutes—enough to reposition the loader .
  
• Continued monitoring revealed intermittent clogging, suggesting internal wear or disintegration inside the pump. A full pump rebuild or replacement may be necessary.
  

User Advice: When to Rebuild or Replace

• If cleaning return flow paths cures the issue temporarily, but the engine fails again soon after, the pumping internals or governor ring may be deteriorating .
  
• Professional refinishing or full service from a certified pump rebuilder is often required if the metering valve or internal leakage persists.
  
• Replacement is sometimes the most reliable solution for heavily used or aged pumps.
  

Useful Troubleshooting Steps in Summary

• Check fuel supply pressure and continuity (pump inlet flow under throttle).
  
• Verify return circuit passage is clear—loosen return fittings to observe flow.
  
• Test solenoid operation and wiring voltage under cranking conditions.
  
• Remove top cover and ensure MV arm moves freely under throttle control.
  
• If possible, use penetrating oil to free the MV arm temporarily—but avoid long-term use without fuel stabilizers .
  

Terminology Glossary

• Injection Pump: High-pressure fuel pump delivering diesel directly to each injector.
  
• Return Line / Tee Fitting: Collects excess injector flow and pump overflow for return to tank.
  
• Metering Valve (MV): Internal pump device controlling delivery volume based on throttle/gov.
  
• Shut-off Solenoid: Electrically actuated valve that stops fuel flow when de-energized.
  
• Fuel Lift Pump: Mechanical or electric pump that pre-delivers fuel to the injection pump inlet.
  

Anecdote From the Field
A dedicated owner shared that after his oil pump failure damaged internal engine components, a rebuild rendered the previously functioning injection pump inoperative. It cracked him up watching the machine repeatedly turn over with no fuel delivery. After persistent cleaning of internal return ports and metering circuit lubricating, it ran long enough to reinstall front attachments. Still, he suspects the internals may fail altogether—emphasizing that even repaired systems may relapse with time.
Conclusion: Clean Flow Is Everything
When an injection pump “won’t work” on a Case 1835C, the answer often isn’t a bad pump—but blocked return channels, stuck metering valves, or incomplete troubleshooting. By systematically observing supply flow, removing return fittings, testing solenoid function, and inspecting internal components, many issues can be resolved without full pump replacement. However, persistent symptoms after cleaning usually mean it’s time for a pro-grade pump rebuild or replacement, especially on older, high-hour machines.
A methodical approach—checking fuel entry, return flow, solenoid feed, and MV free movement—can identify most faults. And while aged pumps may relapse, these techniques often revive equipment that seemed otherwise lost.