6.7 Cummins Lift Pump Failure Symptoms (+Solutions)

The Bosch high-pressure common-rail injector in a 6.7L Cummins engine is fed by a lift pump. This pump delivers fuel at a pressure 3,000 psi greater than that of the 5.9L engine. In this article, we discuss the seven most common signs of lift pump failure in a Cummins engine and offer some tips on how to fix this issue.

6.7 Cummins Lift Pump Failure Symptoms

The lift pump is a critical component of the fuel injection system, and its proper functioning is vital for smooth and efficient engine operation. Watch for these symptoms, as they may indicate impending pump failure. Any of the following factors—or a combination thereof—could suggest an issue with the lift pump on a 6.7L Cummins engine:

  1. Difficulty Starting the Engine: If the lift pump fails, the engine may take longer to start because the pump is responsible for supplying fuel to the injectors. Without a functioning pump, fuel cannot reach the injectors, preventing the engine from starting.
  2. Reduced Fuel Pressure: When the pump fails, the injectors cannot receive sufficient fuel. This results in low fuel pressure, which can adversely affect engine performance. A low-pressure pump may cause the engine to run poorly, misfire, and ultimately stall. This can also damage the injectors and other engine components.
  3. Reduced Compression: Lift pump failure can lead to poor compression and even compressor failure due to inadequate fuel delivery to the cylinder, resulting in poor combustion and reduced engine performance. In extreme cases, a malfunctioning lift pump could cause the engine to stall.
  4. Injector Failure: Lift pump failure can also negatively impact the injectors, potentially leading to their freezing and triggering a series of domino effects that ultimately damage the engine.
  5. Slow Engine Cranking: Lift pump failure can cause cranking issues in the engine due to insufficient fuel supply. This can lead to halting or slow cranking. If your engine has difficulty starting, check if your lift pump is functioning correctly.
  6. Limited Fuel Supply: The fuel injectors, in collaboration with the lift pump, are responsible for supplying fuel to the engine. If either of these components fail, fuel delivery may be disrupted, leading to engine malfunctions, power loss, and decreased fuel efficiency.
  7. Increased Emissions: In some cases, a failing lift pump can damage or cause an injector to fail, causing the engine to run lean and emit more pollutants. The exhaust smoke color can also change, ranging from blue to black.
  8. Increased Fuel Consumption: If the lift pump isn’t functioning properly, the engine will struggle to run due to insufficient fuel. This can lead to increased fuel consumption.
  9. Acceleration Issues: Lift pump failure can affect how quickly the car accelerates, as it can disrupt proper fuel supply to the engine.
  10. Excessive Heat: If the fuel lift pump fails, the engine will not receive fuel at the right pressure. This can cause the engine to overheat because it is not getting enough fuel and is working harder than it should. The lift pump also ensures clean and debris-free operation of the fuel system. If it malfunctions, debris and other impurities can enter, clog the injectors, and damage other components.

Also Read: Car Feels Bumpy When Driving (Causes and Solutions)

Solutions for Lift Pump Failure

Depending on the severity of the problem, several strategies can be used to address issues with the lift pump on a 6.7-liter Cummins engine:

1. Recalibration

The lift pump needs to be correctly calibrated to accurately control the amount of fuel supplied to the engine. If the pump’s calibration is off, it may overfuel the engine, affecting its performance. Hence, correct lift pump calibration is essential for optimal engine performance and fuel efficiency.

2. Restoration

Proper lift pump connection is crucial for its intended operation. If improperly connected, leakage or other issues may occur. Regularly inspect your pump and its connections to ensure they are properly attached. If a connection problem is detected, resolve it by tightening the connections or re-setting them as necessary. If the issue persists, consider replacing the lift pump.

3. Replacement

If your lift pump is worn, shows signs of failure, or is not working properly, replacement may be necessary. This process typically involves the following steps:

  1. Raise the vehicle using jack stands to access the lift pump on the undercarriage.
  2. Disconnect the battery to avoid electrical shocks.
  3. Locate the lift pump, which is usually near the fuel tank, and disconnect the fuel and electrical connectors.
  4. Disconnect the old lift pump and install a new one. Reconnect the fuel lines and electrical connectors and secure the new pump with bolts.
  5. Lower the vehicle off the jack stands and reconnect the battery. Finally, restart the engine to initiate the new lift pump.

Important things to know about the 6.7 liter Cummins Pump

A Cummins lift pump is a type of refueling pump that transfers fuel from the tanks to the injectors in a diesel engine. This pump is often used in heavy engines where high pressure fuel delivery is required. Additionally, when the fuel tank is located below the injector, as is common in sailboats and other boats, these pumps are frequently employed.

Lift pumps comprise a casing, an impeller, and a diaphragm, among other components. The casing houses the pump’s various components and typically features an inlet and outlet port for hose connections. A rotating blade called the impeller facilitates fuel circulation within the pump. The flexible membrane, referred to as the diaphragm, serves as a barrier between the pumping chamber and the engine’s intake manifold, contributing to the suction that pulls fuel into the pump.

Cummins lift pumps are designed for longevity and reliability, often lasting many years. However, inadequate maintenance can lead to premature failure. Regular inspection of the lift pump’s condition and replacement when necessary can help prevent this.


How can I tell whether my lift pump is functioning?

Quickly turn the ignition key to start (without starting the engine) and let it remain in the on position for about 25 seconds to test the lift pump.

What symptoms suggest a failing diesel pump?

Some common signs of a failing fuel pump include jerking or sputtering at high speeds and power loss during acceleration or while climbing an incline.

Can diesel engines run without lift pumps?

Yes, in a stock vehicle that is not modified for increased horsepower, the engine can run for quite some time without a lift pump.

What are common causes of pump failure?

The most common causes include improper lubrication, overheating, and bearing overload due to cavitation from insufficient flow, which puts excessive pressure on the impeller.

How does a vehicle behave when the fuel pump fails?

After starting, the fuel pump continuously supplies fuel to the engine to maintain the vehicle’s speed. If the pump can’t provide a steady flow of fuel at high speed, the engine may sputter and potentially stall.

How can pump failure be avoided?

Always use new gaskets and seals during pump installation. Apply sealant only if the manufacturer specifically recommends it. Incorrect application of sealant can cause issues, especially if the lift pump already has an O-ring, gasket, or seal.

Does a code appear when the fuel pump fails?

Yes, a faulty fuel pump and pressure sensor can trigger the “Check Engine” light and a P0087 error code.

Final Thoughts

Considering the information provided, the importance of a properly functioning lift pump in the Cummins engine can’t be overstated. It ensures proper fuel flow in the engine, and its failure can have serious consequences. Recognizing the signs of impending or complete failure is essential to prevent the problem from escalating into a more complex issue.

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