Replacing Diesel Fuel Pumps In Onan Generators: Step-By-Step Guide

Replacing the fuel pump on an Onan generator can be a challenging task, especially when access to the pump is limited. The fuel pump is responsible for supplying fuel to the generator's engine, and when it fails, the generator may experience starting issues or run for only short periods before shutting down. To replace the fuel pump, one must first gain access to it by removing any components blocking it, such as the control board, solenoid, and cables. Once accessed, the fuel lines are disconnected, and the faulty pump is unscrewed and replaced with a new one. This process can vary in difficulty depending on the specific model of the Onan generator and the level of accessibility to the fuel pump.

Testing the fuel pump

Before replacing the fuel pump, it is important to test it to confirm that it is faulty. Here are some tests you can perform:

• Check the fuel pump fuse: Refer to your owner's manual to locate the fuse box. Find the fuse linked to the fuel pump and inspect it for signs of failure. If the fuse is blown, replace it and try starting the generator. If the new fuse blows, there may be a high amp draw, and further diagnosis is required.
• Check the voltage at the pump: Consult your vehicle's service manual to locate the correct point for voltage testing. Check the voltage to ensure that power is reaching the pump.
• Perform a drop test using a voltmeter: This test checks the power wire and the grounding wire. If there is a difference of more than one volt, there may be an issue with corroded wires or the circuit.
• Perform a fuel pressure test: This test requires a fuel pressure gauge, which can be purchased or borrowed from an auto shop. Locate the fuel pump test point near the fuel injectors and attach the gauge. Start the generator and check the pressure at idle and rated speed. If the pressure does not match the specifications or decreases when revving the engine, the fuel pump needs replacement.
• Test fuel flow: This test is recommended when the generator cranks but does not start or fires once or twice. Remove the return fuel line and attach a piece of fuel hose to the nipple, directing it into an empty container. Press and hold the STOP/PRIME button for one minute. If less than half a pint of fuel is pumped, there may be an issue with the pump or supply lines.
• Test after generator dies: If your generator runs for a while and then dies, test the fuel pump immediately after it shuts down. Disconnect the fuel hose going into the carburetor and direct it into a bucket. Press the generator start or prime button. If the fuel pump is working, you should see a steady flow of fuel into the bucket.

Removing the fuel hose

To remove the fuel hose from your Onan generator, you will need a screwdriver and a drip pan or bucket.

First, disconnect your RV from shore power and disconnect the negative cable from your RV battery. Next, pinch the fuel line between the fuel tank and the fuel filter to prevent fuel flow when you disconnect the hose. Place a drip pan or bucket underneath the left rear of the generator, where the fuel pump is located, to catch any fuel that may leak out.

Now, disconnect the fuel hose from both ends of the fuel pump and fuel filter. The drip pan should catch any fuel that drips out. Be sure to have your drip pan or bucket nearby to catch any fuel that may leak during this process.

Once the fuel hose is disconnected, carefully remove it from the generator. Be sure to handle the hose gently to avoid damaging it, as you will need to reinstall it later. Place the removed hose in a safe location where it will not be damaged or contaminated.

It is important to note that working with fuel can be dangerous, so ensure you take the necessary precautions and perform this task in a well-ventilated area.

Disconnecting the negative cable from the RV battery

Disconnecting the negative cable from your RV battery is an important step when replacing the fuel pump in your Onan generator. Here is a detailed, step-by-step guide on how to do this critical task safely and effectively:

First and foremost, safety should be the top priority when working with any electrical system, especially in an RV. Ensure that you have taken the necessary precautions and referred to the safety guidelines provided by the manufacturer. It is also recommended to wear protective gear, such as gloves and eye protection, to shield yourself from any potential hazards.

Now, let's begin the process:

• Locate the RV battery: The battery is typically located in a designated battery compartment or storage area within your RV. It is usually placed near the generator or in a designated utility area.
• Identify the negative cable: The negative cable is connected to the negative terminal of the battery. It is often black in color and may be marked with a "-" symbol or a black insulation jacket.
• Prepare the necessary tools: You will need a suitable wrench or socket that fits the nut or bolt securing the cable to the battery terminal. Gather these tools before proceeding.
• Disconnect the negative cable: Once you have identified the negative cable, use the appropriate tool to loosen the nut or bolt that secures it to the battery terminal. Do not allow the wrench or socket to touch any other parts of the battery, as it may cause a short circuit. Loosen the connection and remove the cable from the terminal.
• Insulate and secure the cable: After disconnecting the cable, it is important to insulate and secure it properly. Wrap the end of the cable with electrical tape or insulate it using a suitable covering to prevent accidental contact with other metal components. Ensure that the cable does not touch any metal surfaces or create a potential short circuit.
• Store the cable safely: Place the disconnected cable in a secure location away from any potential hazards. Ensure that it does not dangle or touch any engine components. You may need to tie it down or secure it to a nearby structure to keep it safely out of the way.

Remember, this process is crucial for ensuring your safety and preventing any accidental electrical issues while you work on replacing the fuel pump. Always exercise caution and follow established safety protocols when working with electrical systems in an RV.

Locating the fuel pump

To locate the fuel pump, start by identifying the generator's fuel tank and fuel lines. The fuel pump is usually located along the fuel line, which carries fuel from the tank to the engine. In some Onan generators, the fuel pump is situated under the genset base, at the front left corner. It is screwed directly into the inlet of the fuel pump, making it accessible for replacement.

In the case of the Onan RV QD 10000 generator, there is a removable cover on the driver's side rear that appears to be intended for fuel pump access. However, this access point may be blocked by the generator's slide-out framework, requiring creative solutions to gain sufficient clearance.

Before attempting to locate and replace the fuel pump, it is essential to disconnect your RV from shore power and disconnect the negative cable from the RV battery to ensure a safe working environment. Additionally, having a basic understanding of generator components and fuel systems is crucial to successfully locating and replacing the fuel pump.

If you are unsure about the specific location of the fuel pump in your Onan generator, it is always recommended to consult a qualified technician or refer to the generator's service manual for detailed instructions.

Replacing the fuel pump and filter

Step 1: Disconnect Power and Fuel Sources

• Disconnect your RV from shore power.
• Disconnect the negative cable from your RV battery.
• Pinch the fuel line between the fuel tank and fuel filter with vice grips to prevent fuel flow.
• Place a drip pan under the left rear of the generator to catch any fuel that leaks out.

Step 2: Remove Fuel Pump and Filter

• Disconnect the fuel hose from both ends of the fuel pump and fuel filter.
• Remove the bolts holding the fuel pump and remove the fuel pump and filter.

Step 3: Install New Fuel Pump and Filter

• Screw the new fuel filter into the new fuel pump.
• Screw the new fuel pump and filter into place.
• Attach the fuel lines to the new fuel pump/filter.

Step 4: Reassemble and Test

• Reinstall all the components that were removed to access the fuel pump.
• Remove the vice grips from the fuel line and check for leaks.
• Reconnect power to your battery and shore power.
• Test the generator by priming the pump and pressing the start button.

Frequently asked questions