Fuel Delivery Troubles on the Case 580L Series II

[MikePhua]

The Case 580L and Its Mechanical Lineage
The Case 580L Series II backhoe loader was introduced in the mid-1990s by Case Corporation, a company with roots dating back to 1842. Known for pioneering agricultural and construction machinery, Case had already established the 580 series as one of the most successful backhoe lines in North America. The 580L featured a naturally aspirated Cummins 3.9L four-cylinder diesel engine, delivering around 75 horsepower and paired with a mechanical fuel system. With over 100,000 units sold across various 580 models, the 580L became a staple on job sites, farms, and municipal fleets.
Its mechanical simplicity made it popular among owner-operators, but that same simplicity can lead to confusion when troubleshooting fuel delivery issues—especially after routine maintenance like replacing the fuel/water separator.
What Happens When the Fuel System Airlocks
After replacing the fuel/water separator, it’s common for air to enter the fuel lines, causing an airlock. In mechanical diesel systems, air prevents the lift pump from delivering fuel to the injection pump, resulting in a no-start condition. The manual priming lever on the lift pump is designed to purge this air, but if the engine stopped with the pump cam lobe holding the lever down, the priming action becomes ineffective.
This situation is deceptively simple: the pump arm is mechanically pinned by the camshaft, preventing diaphragm movement. The solution is to “bump” the starter—briefly crank the engine without starting it—to rotate the camshaft and reposition the pump arm. Once the cam releases the arm, the manual lever regains full travel and can begin drawing fuel.
Identifying the Bleed Screw and Priming Procedure
On the Bosch-style injection pump used in the 580L, the bleed screw is typically located near the top of the pump body. It resembles a small screw threaded into a larger hex nut. Opening this screw allows trapped air to escape during priming. The correct procedure is:

• Unlock the manual priming lever by rotating it counterclockwise
  
• Pump the lever until resistance builds and fuel flows from the bleed screw
  
• Close the bleed screw once fuel is free of bubbles
  
• If fuel still doesn’t reach the injectors, crack open the injector lines at the pump
  
• Continue priming until fuel escapes from the loosened lines
  
• Retighten and attempt to start the engine
  

This method ensures that both the lift pump and injection pump are purged of air. If the diaphragm inside the lift pump doesn’t return after pushing the lever, it may indicate internal air blockage or a plugged supply line.
Understanding Diaphragm Behavior and Spring Pressure
The lift pump operates via a diaphragm that moves in response to camshaft rotation or manual lever action. When pushing the lever down, the diaphragm is pulled back against spring pressure. If the diaphragm returns slowly, fuel is being drawn. If it doesn’t return, the pump is either full or blocked.
A common misconception is that pushing the lever down pumps fuel. In reality, the downward motion pulls the diaphragm back, and the upward return is what pushes fuel forward. If the lever feels unusually stiff or floppy, it may be due to vacuum resistance or internal wear.
Supply Line Obstruction and Vacuum Symptoms
If the priming lever becomes harder than usual to push, it may be pulling a vacuum—suggesting a plugged fuel line or blocked tank outlet. In such cases:

• Inspect the fuel tank for debris or collapsed pickup tubes
  
• Check the fuel line for kinks, pinched sections, or internal delamination
  
• Replace old rubber hoses with ethanol-resistant fuel line
  
• Clean or replace the water separator and filter housing
  

A contractor in Arizona once discovered that his 580L wouldn’t prime after sitting idle for a month. After tracing the issue, he found a mud dauber nest inside the tank outlet. Clearing the obstruction restored full fuel flow.
Starter Cranking and Camshaft Positioning
If the manual lever shows no resistance, the camshaft may be holding the pump arm down. Bumping the starter—briefly engaging the starter motor without attempting a full start—can rotate the camshaft and release the arm. This technique is widely used in field repairs and avoids unnecessary disassembly.
One diesel technician in Queensland noted that he routinely bumps the starter when servicing older Case machines, especially when replacing filters or lift pumps. He emphasized that understanding camshaft-driven components is key to diagnosing fuel delivery issues.
Recommendations for Reliable Fuel System Maintenance
To prevent airlocks and ensure consistent fuel delivery on the Case 580L:

• Always pre-fill the fuel/water separator before installation
  
• Prime the system immediately after filter replacement
  
• Inspect and clean the bleed screw annually
  
• Replace fuel lines every 5–7 years to prevent internal collapse
  
• Keep the tank at least half full to reduce air ingestion
  
• Use clean diesel and avoid refueling from contaminated sources
  

For machines stored long-term, consider installing a fuel shutoff valve and draining the separator before storage. This reduces microbial growth and water accumulation.
Conclusion
Fuel delivery problems on the Case 580L often stem from airlocks, camshaft positioning, or supply line obstructions. By understanding the mechanical behavior of the lift pump and diaphragm, operators can resolve no-start conditions quickly and confidently. With proper maintenance and a few field-tested techniques, the 580L continues to be a dependable workhorse across construction and agricultural landscapes.