Cummins code 559 indicates a fuel pressure problem within your engine. This article dives into potential causes and troubleshooting steps to help resolve this issue. While this code doesn’t directly translate to a specific Cummins fault code, it likely points to low fuel pressure issues that can trigger various Cummins engine codes related to fuel delivery. Therefore, we’ll approach this problem as a general low fuel pressure diagnostic process.
Pinpointing the Source of Low Fuel Pressure
Low fuel pressure can stem from numerous sources. Before delving into Cummins-specific diagnostics, start with fundamental checks:
Fuel Supply: From Tank to Engine
- Fuel Level: Ensure sufficient fuel in the tank. A low fuel level can starve the engine, especially under load. Consider the vertical distance between the fuel tank and the engine. If the tank is significantly lower, the fuel pump has to work harder.
- Fuel Lines: Inspect for kinks, blockages, or leaks in the fuel lines. A restricted fuel line significantly reduces the flow rate to the engine. Disconnect fuel lines and visually inspect them for any damage or debris.
- Fuel Filters: Clogged fuel filters restrict fuel flow. Replace fuel filters according to the manufacturer’s recommended intervals. Consider using a clear bowl fuel filter housing to visually monitor for contamination.
- Fuel Pickup Tube: Debris or a malfunctioning pickup tube within the tank can impede fuel delivery. Check for blockages or damage. Applying compressed air to the fuel line (with the fuel cap removed) can help dislodge obstructions in the pickup tube. Listen for bubbling in the fuel tank to confirm air passage.
- Fuel Return Line: A restricted return line can cause excessive back pressure, leading to low fuel pressure at the engine. Disconnect the return line and blow through it. It should be clear with minimal resistance. If significant backpressure exists, investigate for clogs or kinks.
Fuel Pump Diagnosis
- Electric Fuel Pump Testing: If equipped with an electric fuel pump, check for proper voltage and current draw. Listen for the pump to activate when the ignition is turned on. If an external electric fuel pump is used for testing, ensure it can deliver sufficient pressure (around 10 PSI) and flow rate (30-40 GPH). Test the pump by running it into a separate container to verify its output before connecting it to the engine. Monitor the vacuum gauge during this test.
- Mechanical Fuel Pump Inspection: Mechanical fuel pumps can wear out over time. Check for leaks or unusual noises. A fuel pressure gauge installed on the filter head will help monitor pressure while running the engine. If the pressure is consistently low, the mechanical pump may be failing.
Further Diagnostics and Considerations
- Engine Load and Fuel Pressure: Observe fuel pressure readings under different engine loads. A drop in pressure under load may indicate a failing pump or restricted fuel supply.
- Throttle Position and Fuel Demand: The engine control module (ECM) adjusts fuel delivery based on throttle position. A faulty throttle position sensor or ECM issue could contribute to fuel pressure problems. However, a consistently low fuel pressure, regardless of throttle position, usually points to a fuel supply problem. An increase in throttle position with no corresponding rise in actual fuel pressure might indicate a fuel delivery issue.
Addressing Code 559
Resolving Cummins code 559 (or general low fuel pressure issues) requires systematic troubleshooting. Address fuel supply constraints, verify pump functionality, and check for restrictions in the fuel system. Remember to consult your Cummins engine service manual for specific diagnostic procedures and recommended fuel pressure specifications for your engine model. By methodically eliminating potential causes, you can efficiently pinpoint and resolve the root of the problem. Using a fuel pressure gauge is crucial for accurately diagnosing low fuel pressure issues.
