Mercedes Mullins
Cummins is a relatively simple diesel engine commonly found in Dodge trucks. However, they are known to experience hard start conditions, where the engine cranks but does not start. This can be caused by various issues, such as weak lift pumps, failed injection pumps, or fuel sensor voltage issues. In some cases, the fuel system may be to blame, with fuel draining back to the tank due to leaks or blockages in the lines. To troubleshoot a non-starting Cummins engine, it is recommended to check the lift pump pressure, pressure relief valve, and return rate of the injectors.
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What You'll Learn
A faulty lift pump
One of the most common symptoms of a faulty lift pump is a noticeable power loss. This can manifest as a reduction in the engine's ability to maintain RPMs in the upper ranges, causing the engine to ""lay down" or sputter when in drive. In some cases, the engine may even stall after running for a few minutes, requiring a restart.
Another sign of a faulty lift pump is difficulty in starting the engine, particularly when the vehicle has been parked on level ground for an extended period. This is often due to fuel draining back into the tank, which can be caused by a vacuum in the system or issues with the fuel return line. A leaking fuel tank or a faulty fuel pressure regulator can also cause fuel to drain back, leading to hard starting.
To diagnose a faulty lift pump, it is recommended to check the lift pump pressure at idle and while cruising. Additionally, inspecting the return rate of injectors and testing the pressure relief valve can help identify potential issues.
It is important to address lift pump issues promptly as running the engine for long periods with a faulty lift pump can cause further damage, potentially leading to the failure of the main injection pump.
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A blocked vent
A blocked fuel tank vent can cause issues with the fuel system of a Cummins engine. The vent, located at the top of the tank, allows air to enter and exit the tank, equalising pressure. When the vent is clogged, air cannot enter the tank, creating a vacuum that can affect the fuel pump's ability to draw fuel, leading to hard starts or extended cranks.
One symptom of a blocked vent is a noticeable increase in air pressure within the fuel tank when filling up. This pressure can cause the tank to temporarily deform, sucking inwards before returning to its normal shape when the cap is removed. This inward deformation indicates a vacuum within the tank, which can be caused by a blocked vent.
Another sign of a blocked vent is the sound of rushing air when the fuel cap is removed. This sound suggests that the tank is under pressure, and the sudden release of air occurs as the pressure equalises with the atmosphere. This issue can be further confirmed by leaving the fuel cap slightly loose; if the tank is under pressure, the cap will pop off as the air escapes.
To resolve a blocked vent, the vent itself must be cleaned or replaced. One method is to use a piece of clear plastic tubing or hose (approximately 1/4" in diameter) and attach it to the vent nipple. The hose is then routed near the bottom of the bed, and a small engine fuel filter is attached to the end. This setup allows the vent to function while preventing the buildup of debris.
It is important to refer to the vehicle's manual for specific instructions and safety precautions when addressing a blocked vent. Additionally, some users have suggested adding an additional vent or drilling a small hole in the underside of the fuel cap to alleviate the pressure buildup caused by a blocked vent.
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A clogged pickup screen
To address this issue, it is recommended to “drop the tank” to access and clean or replace the clogged pickup screen. This process involves removing the fuel tank from the vehicle to access the pickup screen for inspection and cleaning. In some cases, it may be necessary to replace the screen if it is severely clogged or damaged.
Additionally, it is worth considering an in-tank pump conversion or installing an aftermarket in-tank lift pump to improve the fuel system's performance and prevent future issues. This can be done while the tank is dropped during the cleaning or replacement of the pickup screen.
It is important to note that a clogged pickup screen may not always be the root cause of the issue. Other potential culprits could include problems with the lift pump pressure, pressure relief valve, return rate of injectors, fuel control actuator (FCA), or the injection pump itself. Therefore, it is recommended to start at the beginning of the fuel system and work your way forward, checking these components to identify and address the specific cause of the issue.
Furthermore, some Cummins owners have reported instances of collapsed fuel tanks, which can be incorrectly diagnosed as a clogged in-tank pump assembly screen. In such cases, it is important to inspect the vents on top of the tank, as they can collect dirt and water, leading to potential clogging issues.
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A faulty injection pump
One of the most common issues with the Cummins engine is a faulty fuel transfer or lift pump. This can be caused by a number of factors, including a blocked fuel filter, a faulty fuel pickup in the tank, or a leak in the fuel system. When the lift pump is faulty, it may not be able to generate enough pressure to lift the fuel from the tank, causing the engine to stall or fail to start.
To diagnose a faulty lift pump, it is recommended to check the pressure at idle and while cruising. If the pressure is inadequate, the lift pump may need to be replaced. Additionally, checking the return rate of the injectors and testing for leaks in the fuel system can help identify if the lift pump is the root cause of the issue.
Another potential issue is low fuel pressure, which can affect the performance and lifespan of the injection pump. If the pressure drops below 5 PSI, it can compromise the injection pump. This can be caused by a clogged filter or a low-pressure system, and it may be necessary to install a high-quality lift pump to maintain adequate cooling flow while the engine is running.
In some cases, the injection pump itself may be faulty. This can be due to a number of factors, including a faulty computer board, incompatibility with new ultra-low sulfur fuels, or a leaking fuel pump. It is important to refer to the service manual for guidance on fuel injection pump replacement and to use genuine parts to ensure optimal performance and avoid further complications.
To summarise, a faulty injection pump can be caused by a range of issues, including a faulty lift pump, low fuel pressure, or a faulty injection pump itself. By following diagnostic procedures, such as checking pressure and testing for leaks, these issues can be identified and addressed to ensure the Cummins engine lifts fuel from the tank effectively.
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A faulty fuel control actuator
To test an FCA, compare commanded versus actual rail pressure with a scan tool. Unplugging it should spike pressure—if not, the FCA may be faulty. Actual and commanded pressure can be monitored on a scan tool and compared. The most common symptom of failure is a varying or unstable idle.
If you have a 2000 24V Cummins and are experiencing hard-start issues, it could be due to fuel draining back to the tank. This can happen when the truck is parked level for more than an hour. However, if the truck is parked facing downhill, it starts as usual. In this case, the fuel is not the issue, but rather air entering the return line. To fix this, you need to replace the O-rings on the cross over tubes.
If you have a 2003-2007 5.9 Cummins and are experiencing hard-start issues, rough idle, or surging, the FCA is a likely culprit. You can test, diagnose, and replace the FCA. The most common cause of FCA failure is fuel contamination, wiring issues, or solenoid failure. Poor fuel quality or a failing injection pump can also be factors.
If you have a 2003 5.9 Cummins and are experiencing no-start issues, it could be due to a faulty lift pump or a clogged fuel filter. In this case, replacing the lift pump and fuel filter may fix the issue.
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Frequently asked questions
There could be a number of reasons for this. Firstly, check for a fuel leak. If there is no leak, check the lift pump pressure, both at idle and cruise. If the pressure is inadequate, the lift pump may be weak. Other potential issues include a faulty pressure relief valve, a blocked vent, or a clogged pickup screen.
A faulty lift pump may cause the engine to crank but not start. You may also experience hard start conditions, where the engine takes longer to start, or it may run for a few minutes and then shut off.
To test the lift pump, connect it to a power supply that matches its working voltage (either 12-VDC or 24-VDC) and ensure it can supply the minimum amperage, which is typically around 6 amperes. Place the pump into a clean container to catch the fuel output and turn on the power supply. Confirm that the pump is pumping a minimum amount of fuel as marked in the manufacturer's manual.
Common failure points for a Cummins lift pump include weak lift pumps and failed VP44 injection pumps. To diagnose these issues, use an OBD-II scanner to scan the truck for codes such as P0216, P1689, and P0253.
If you have identified that the lift pump is faulty, you may need to replace it. There are new types of fuel lift pumps available that are designed to operate both lift pumps under the same load, extending the life of the system. You can also refer to the manufacturer's manual for specific instructions and recommendations.
