Replacing Fuel Pump In Onan Marquis 5000: Step-By-Step Guide

The Onan Marquis 5000 is a generator that can be found in RVs and motorhomes. The fuel pump on the Marquis 5000 is located on the top right rear of the generator and can be difficult to access. In this article, we will provide a step-by-step guide on how to change the fuel pump on a 96 Onan Marquis 5000, including tips and tricks from other Marquis 5000 owners who have successfully replaced their fuel pumps.

Troubleshooting a faulty fuel pump

Step 1: Check for Basic Issues

Before jumping to conclusions, it's essential to rule out some basic issues. Start by checking the fuel pump for any signs of damage or wear and tear. Ensure that the fuel pump is properly connected and there is no corrosion on the connectors. If you notice any corrosion, using WD-40 or a similar product to clean the connectors can help.

Step 2: Test the Voltage

If the fuel pump is not receiving power, the problem could lie in the voltage supply. Hardwire the fuel pump to a separate battery. If it runs fine with this alternative power source, the issue may be with the voltage supply to the pump.

Check the wiring diagram and the battery voltage while cranking, both at the pump and the battery, to ensure there is no voltage drop. A voltmeter will come in handy for this step.

Step 3: Check for Air Leaks

If the fuel pump is receiving power but still not functioning optimally, there could be an air leak in the fuel system or around the carburetor. This can disrupt the fuel supply and affect the performance of the pump.

Step 4: Replace the Fuel Pump

If the above steps do not resolve the issue, it may be time to replace the fuel pump. The Onan Marquis 5000 fuel pump is located on the top right rear of the generator and can be challenging to access. You may need to tilt the generator forward or even remove it from the RV to access the pump.

When replacing the fuel pump, consider opting for a more affordable alternative, such as the Carter P4070 In-Line Electric Fuel Pump, which is an exact replacement for the Onan pump. Additionally, ensure that you have the right tools and, if necessary, don't hesitate to seek the assistance of a mobile RV technician.

Step 5: Post-Replacement Checks

After replacing the fuel pump, it's crucial to perform some checks to ensure everything is functioning correctly. Start the generator and let it run for an extended period to ensure the pump is working as expected. Also, keep an ear out for any unusual noises that could indicate a problem.

Step 6: Seek Professional Help

If you're unsure about any aspect of the troubleshooting or replacement process, don't hesitate to consult a professional. Generator mechanics or RV technicians can provide expert guidance and ensure that the issue is correctly identified and resolved.

Remember, safety should always be a priority when working with generators and their components. Refer to the generator's manual or seek expert advice if you have any doubts about the procedures or safety precautions.

Checking the fuel shut-off valve

To check the fuel shut-off valve on your Onan Marquis 5000 generator, you'll need to perform a few tests to diagnose the issue.

Firstly, check if your generator is receiving fuel by taking off the fuel line just below the carb and filter and observing if gas is flowing when cranking. If there is no gas flowing, this could indicate an issue with the fuel shut-off valve or the fuel pump.

To test the fuel shut-off valve specifically, you can remove it from the generator and connect it directly to a 12-volt battery. If there is no response from the valve, it may be faulty and need replacement.

Another way to test the valve is to apply pressure to the filler cap at the tank with a small air compressor, while observing the fuel flow at the pump with the hose disconnected. If fuel flows through the hose, it indicates that the valve is functioning correctly.

Additionally, you can try to siphon gas through the gen fuel line. If you are unable to get any gas through, there could be a blockage in the line or the fuel sock in the tank might be stopped up.

It is also recommended to replace the fuel filter and check the fuel line for any breaks or leaks to ensure that the issue is not related to the fuel delivery system.

Please note that these instructions are based on a user's experience and may not be comprehensive for your specific situation. Always refer to official maintenance guidelines or seek professional assistance if you are uncomfortable performing these tasks.

Locating the fuel pump

Firstly, it is important to understand the context in which you are working. The fuel pump on the Onan Marquis 5000 is typically located within the generator itself, and in some cases, it may be housed in a sound box or enclosure. This makes accessibility a challenge, as you will need to find a way to reach the pump without causing damage to the generator or its housing.

To begin locating the fuel pump, start by identifying the fuel hose that runs from the carburettor. This hose will lead you to the fuel pump, which is usually found at the rear of the generator, often on the top right-hand side. In some cases, you may need to tilt or lift the generator to access this area, as it can be quite tight. If your generator is housed in a sound box, you may need to remove the top cover to gain access.

Before attempting any maintenance or repairs, ensure that you have adequate knowledge of generator mechanics and safety procedures. It is crucial to disconnect the power source to the generator before proceeding. Additionally, have the necessary tools and safety equipment on hand, such as gloves and eye protection.

Once you have identified the fuel hose, carefully trace it to its source, which should be the fuel pump. The fuel pump is responsible for delivering fuel from the tank to the carburettor, so it is an essential component of the generator's fuel system. You may need to remove or loosen mounting bolts to access the pump completely. Be cautious when handling the fuel pump, as it is a delicate component, and any damage could result in fuel leaks or other issues.

In some cases, you may find a fuel filter attached to the outlet port of the fuel pump. This is an important discovery, as it indicates that there are two fuel filters in the system, which is not always common knowledge. Ensure that you take note of this during your maintenance or repair work to avoid any complications.

Disconnecting the fuel pump wires

Before beginning any work on your generator, it is important to ensure your safety. Make sure the generator is switched off and allow sufficient time for the engine and its components to cool down. Wear protective gear, such as gloves and eye protection, to shield yourself from any fuel residue or debris.

Now, let's get started on disconnecting the fuel pump wires:

• Locate the Fuel Pump: The fuel pump on the 96 Onan Marquis 5000 is typically located on the top right rear of the generator. To access it, you may need to tilt the generator forward or lower it, as it can be challenging to reach.
• Identify the Wires: Once you have located the fuel pump, identify the wires connected to it. There should be a connector joining the wires to the fuel pump.
• Apply WD-40: If the wires are difficult to disconnect, apply a small amount of WD-40 to the connector. This can help loosen any corrosion or buildup that may be holding the wires in place.
• Carefully Disconnect the Wires: Using a gentle back-and-forth motion, carefully pull the wires apart from the connector. Be cautious not to rip the wires or damage the connector. If they are still difficult to separate, try wiggling the connector gently while pulling on the wires.
• Set the Wires Aside: Once the wires are disconnected, set them aside in a safe place where they will not be disturbed. Make sure to keep them away from any flammable materials or sources of heat.

Remember to take your time and work carefully when disconnecting the fuel pump wires. It is important to avoid damaging the wires or any other components. Always refer to the generator's manual or seek professional guidance if you are unsure about any steps.

In the next section, we will discuss removing the old fuel pump and preparing to install the new one.

Replacing the fuel pump

The fuel pump on the 96 Onan Marquis 5000 is located on the top right rear of the generator. To access and replace the fuel pump, follow these steps:

• Prepare the generator: Support the outer edge of the generator with a floor jack. Remove all the mounting bolts except for one at the rear on each side, which should only be loosened.
• Tilt the generator: Lower the jack to tilt the generator forward at a 30-45 degree angle. This will provide enough space to remove the top cover and access the fuel pump.
• Manage the wiring: Depending on the available slack, you may need to disconnect some of the wiring.
• Access the fuel line connections: These are typically reached through the bottom of the generator.
• Purchase a replacement fuel pump: You can find suitable replacement fuel pumps online or at auto parts stores. The Carter P4070 In-Line Electric Fuel Pump is an exact replacement for the Onan Marquis 7000, and a similar model may be available for the Marquis 5000. You can also find less expensive options, such as the Mr Gasket 42 S low-pressure fuel pump.
• Install the new fuel pump: Place the new fuel pump in the same position as the old one and secure it with the mounting bolts. Ensure that the fuel line connections are secure.
• Reconnect the wiring: Reattach any wiring that was disconnected during the process.
• Test the generator: Once the new fuel pump is installed, test the generator to ensure it is functioning properly.

Note: Some people have reported success in finding less expensive fuel pumps that are compatible with the Onan Marquis 5000. However, it is important to ensure that any replacement pump meets the required specifications, especially regarding pressure (PSI).

Additionally, if you are having difficulty disconnecting the wires from the old fuel pump, you may need to use WD-40 or a similar product to address potential corrosion in the connector. Be gentle to avoid ripping the wire out of the connector.

Frequently asked questions