Adjusting Fuel Mixture: Onan 4000'S Performance Guide

The Onan 4000 is a generator that requires regular maintenance to keep it running smoothly. One aspect of this maintenance is changing the fuel mixture, which can be done by adjusting the fuel filter and pump. This process can be tricky, as the fuel pump and filter are located in a tight space behind and under other components, such as the starter solenoid, air filter, and ECU. However, with the right tools and knowledge, it is possible to access and replace these parts. Some people choose to relocate the fuel pump and filter outside of the generator housing to make future maintenance easier.

Replacing the fuel pump

The fuel pump on an Onan 4000 is located behind and under the starter solenoid, air filter, and the large ECU. This makes it difficult to access. However, with the right tools and some patience, you can replace the fuel pump without dropping the genset. Here is a step-by-step guide on how to do it:

Tools Required:

• T30 bit with a 3-inch extension
• Ratchet
• Flat screwdriver
• Needle-nose pliers
• Vise Grips
• 9/16 normal and 1/2 deep sockets
• Multimeter
• Catch pan
• Yellow Teflon tape

Steps:

• Use a multimeter to confirm 12 VDC between the near terminal of the generator solenoid and ground.
• Disconnect the RV (house) battery positive lead, ensuring the cables cannot reconnect themselves.
• Disconnect any shoreline or solar power.
• Check the solenoid again to ensure no power is going to the generator.
• Put a pan under the front of the generator.
• Clamp off the fuel supply line with Vise Grips and remove the fuel line from the fuel filter.
• Remove the fuel filter with a 1/2-inch deep socket.
• Remove the outer nut on the solenoid post, releasing the large hot cable and small white ring terminal.
• Remove the T30 screw holding the ignition module.
• Disconnect the plug in the bulkhead by prying the tabs outward to the left and right.
• Remove the ignition module and set it aside.
• Remove the lower plug in the bulkhead by prying open the tabs on the sides with a small flat blade screwdriver.
• Mark one pair of the spade terminals on the solenoid so they go back correctly.
• Move the solenoid up by the air filter so it is out of the way.
• Remove the outside T30 screws holding the base plate that the solenoid sits on.
• Wiggle the plate side to side until the hidden tab in the rear comes loose and pull it out.
• Now you can access the front T30 screw that holds the fuel pump in place.
• Wiggle the pump to loosen the rear tab and pull the pump towards you to access the connection to the carb fuel line.
• Before removing the fuel line to the carb, clean around the pump to prevent dirt from getting into the new pump.
• Use needle-nose pliers to compress the hose clamp and pull the hose off.
• Disconnect the two power supply wires, noting what they connect to.
• The old pump is now out and you can begin reassembly.
• Install the fuel filter before inserting the new pump.
• Pull the carb hose up and insert the new pump, being careful not to get any dirt into the connection.
• Expand the hose clamp with pliers and move it into position on the hose.
• Connect the black lead to a circular plate where the wires go to ground.
• Connect the light-colored lead to the insulated connector.
• Shove the far side tab of the pump into its slot.
• Use the T30 extension to start the screw on the near side of the pump, then tighten it with the ratchet.
• Slide the base plate in so its far tab goes into its slot and reinstall the two T30 screws to secure the plate.
• Push the ignition module into its slot and install the front T30 screw.
• Pull the solenoid down, hook the far side to its tab, and install the front T30 screw so it is firmly in position.
• Reconnect the two spade connectors to the solenoid, ensuring the marked pair goes back correctly.
• Put the white ring terminal on the solenoid post, then the big positive cable, and tighten the nut.
• Reconnect the two bulkhead connectors, making sure both tabs snap securely.
• Look over the generator to ensure everything is in place.
• Reconnect the fuel supply line and the cover plate on the front of the generator.
• Reconnect the positive battery lead.
• Confirm that nothing has been forgotten and that the new pump works by firing up the generator.
• Check for any fuel leaks.

Relocating the fuel pump

When relocating the fuel pump on an Onan 4000 generator, there are a few key considerations and steps to keep in mind. Firstly, it is important to assess the accessibility of the pump and decide if relocation is necessary. In some models, the fuel pump and filter are bolted to the floor of the genset, requiring the removal of multiple components for access. This can be a challenging task, especially for those who are less experienced with electronics.

If relocation is indeed the best option, the first step is to carefully remove the old fuel pump. This process involves disconnecting the pump from the carb fuel line, power supply wires, and fuel supply line. It is crucial to have the necessary tools, such as screwdrivers, pliers, sockets, and a ratchet, to safely remove the pump. Once the old pump is out, the next step is to choose an appropriate location for the new pump. Some people choose to mount the new pump outside of the genset housing, bolted to the framework under the RV, for easier access.

When installing the new fuel pump, it is important to ensure that the connections are secure and that there are no leaks. This may involve using Teflon tape on the connections and carefully tightening any screws. Additionally, a longer fuel line may be required to reach the new location of the pump. It is also recommended to install a 2-way valve in the fuel line, allowing the genset to run off the RV tank or a standalone gas can.

Finally, before concluding the relocation process, it is crucial to test the new pump by firing up the generator and checking for any fuel leaks. This ensures that the pump is functioning correctly and that all connections have been properly secured.

By following these steps and considerations, relocating the fuel pump on an Onan 4000 generator can be a manageable task, offering improved accessibility and ease of future maintenance.

Replacing the fuel filter

The fuel filter on an Onan 4000 generator is an inexpensive part that should be replaced every two years to keep the generator in good condition. The process is straightforward and can be completed in under 15 minutes. Here is a step-by-step guide to replacing the fuel filter:

Step 1: Prepare the Generator

Before beginning any work on the generator, it is crucial to ensure that the power is disconnected. Use a multimeter to confirm there is no power between the generator solenoid and the ground. Disconnect the RV (house) battery positive lead, as well as any shoreline or solar power connections. Recheck the solenoid to ensure that all power has been disconnected. Place a pan under the front of the generator to catch any spills or leaks.

Step 2: Access the Fuel Filter

The fuel filter is located behind and under the starter solenoid, air filter, and the large ECU. To access the fuel filter, you will need to remove these components. Use a 9/16-inch socket to remove the plate covering the front of the generator and the fuel supply line. Clamp off the fuel supply line with vise grips and remove it from the fuel filter.

Step 3: Remove the Old Fuel Filter

The fuel filter is screwed into the suction port of the fuel pump. Use a deep socket, likely a 9/16-inch, to remove the old fuel filter. Be sure to plug or pinch off the fuel line to prevent leakage. Slowly turn the fuel filter counterclockwise to unscrew it from the fuel pump. Be cautious as the filter will be full of gasoline.

Step 4: Install the New Fuel Filter

Apply a small amount of high-temperature thread sealant to the base of the threads on the new fuel filter. Insert the new fuel filter into the oval hole, connecting it to the fuel pump. Take care to ensure that the threads go on straight and are not crossed. Tighten the fuel filter with a socket, being careful not to overtighten.

Step 5: Reassemble the Generator

Once the new fuel filter is securely in place, replace the rubber grommet and fuel line. Reinstall the plate covering the front of the generator and the fuel supply line. Reconnect the positive battery lead and any other disconnected components. Check that all parts are securely in place and reconnected.

Step 6: Test the Generator

After completing the fuel filter replacement, test the generator to ensure it is functioning properly. Fire up the generator and check for any fuel leaks.

By following these steps, you can replace the fuel filter on your Onan 4000 generator, ensuring its optimal performance and preventing potential issues caused by a clogged or faulty fuel filter.

Changing the fuel filter without removing the pump

The fuel filter on an Onan 4000 generator can be replaced without removing the pump. This can be done in a few simple steps, but it is important to take the necessary precautions to ensure safety and avoid any fuel leaks.

First, make sure you have the right tools for the job. You will need a deep socket, which is typically a 9/16", a ratchet, a flat screwdriver, needle-nose pliers, Vise Grips, and a new fuel filter. It is also recommended to have a strong LED light to see inside the generator and a catch pan to collect any spilled fuel.

Once you have gathered the necessary tools, follow these steps:

• Disconnect the RV (house) battery positive lead and any shoreline or solar power connections. Confirm that there is no power left in the generator using a multimeter.
• Place a catch pan under the front of the generator to collect any spilled fuel.
• Clamp off the fuel supply line with Vise Grips and remove the fuel line from the fuel filter. Plug or pinch off the fuel line to prevent leakage.
• Remove the old fuel filter by slowly turning it counterclockwise with a deep socket. Be careful when removing the old fuel filter as it will be full of gasoline.
• Prepare the new fuel filter by applying a small amount of Permatex High-Temperature Thread Sealant at the base of the threads.
• Insert the new fuel filter into the oval hole, ensuring that the threads go on straight and are not crossed. Tighten the fuel filter with a socket, being careful not to overtighten.
• Reattach the fuel line and rubber grommet to the new fuel filter.

By following these steps, you can replace the fuel filter on your Onan 4000 generator without removing the pump. This will help keep your generator running smoothly and prevent any issues caused by a clogged or faulty fuel filter.

It is important to consult your generator's manual or seek professional assistance if you are unsure about any part of the process.

Using an inline fuel filter

Step 1: Sizing and Selection

Before purchasing an inline fuel filter, ensure that it is the correct size and compatible with your Onan 4000 generator. The fuel filter should have the appropriate micron rating and flow rate to handle the fuel demands of your generator. Consult your generator's manual or seek advice from an expert if needed. Additionally, consider using a high-quality filter to ensure effective filtration and minimise the need for frequent changes.

Step 2: Mounting the Filter

Choose a suitable location for mounting the inline fuel filter. A common practice is to mount it on the RV's frame or somewhere easily accessible. This location should provide adequate space and stability for the filter while being close enough to the generator's fuel line to minimise fuel pressure loss. You may need to measure the length of the fuel line required and ensure it's long enough to reach the new filter location.

Step 3: Disconnecting the Old Filter

Before installing the inline fuel filter, you'll need to disconnect the old built-in fuel filter. Refer to your generator's manual for specific instructions on how to access and remove the old fuel filter. Remember to plug or pinch off the fuel line to prevent fuel leakage during this process. You may also need to remove other components, such as the starter solenoid, air filter, and ECU, to gain access to the fuel filter.

Step 4: Installing the Inline Fuel Filter

Now, install the inline fuel filter in the new location. Secure it firmly to the frame or chosen mounting point. Ensure that the fuel line from the generator can reach the new filter location, and use appropriate fittings and clamps to connect the fuel line securely to the filter. You may need to cut and replace the fuel line if it's too short or use additional fuel line extensions.

Step 5: Testing and Finalising

Once the inline fuel filter is installed, check for any fuel leaks at the connections. Tighten any clamps or fittings as needed. Start the generator and observe it for a while to ensure that it's running smoothly and that the new filter is functioning correctly.

By following these steps, you'll be able to set up and use an inline fuel filter on your Onan 4000 generator, making future filter changes more accessible and convenient. Remember to choose a high-quality filter and consult experts or your generator's manual if you have any questions during the process.

Frequently asked questions