Checking Fuel Pump Pressure: Outboard Maintenance Guide

If you're experiencing issues with your outboard engine, such as sputtering, misfiring, or increased fuel consumption, you may have a faulty fuel pump. Outboard fuel pumps are different from those in cars and rarely fail, but it's important to know how to check and troubleshoot them to ensure a smooth boating experience. This guide will take you through the process of checking your fuel pump pressure and highlight some common issues to look out for. By following these steps, you can identify and address any problems before they become more serious, saving you time and money.

Check the fuel tank and gauge

Checking the fuel tank and gauge is an important step in troubleshooting fuel pump pressure problems in outboard motors. Here is a detailed guide to help you through the process:

Locate the Fuel Tank and Gauge:

The fuel tank is typically located at the back or aft of the boat, and most boats provide access ports for the fuel tank. If you cannot find the access port, refer to your boat's manual or seek assistance from a marine technician. Once you have located the fuel tank, identify the fuel gauge, which is usually marked with a "+" or "I" symbol.

Check the Fuel Gauge for Power:

Turn on the engine's ignition and use a multimeter to probe between the ground and the positive terminal on the back of the gauge. If there is no voltage (12 volts), the issue is likely with the ignition circuit, and the gauge is probably functioning correctly. If there is voltage at the gauge, the problem may lie with the sender, the gauge, or its wiring.

Disconnect the Sending Wire:

With the power still running to the gauge, locate the sending wire, which will be marked with an "S" at the back of the gauge. Disconnect this wire, and observe the gauge. If the gauge jumps to its highest possible reading, the gauge is functioning correctly, and you can move on to the next step. If the gauge does not respond, it is faulty and needs to be replaced.

Test the Ground Connection:

Another test is to jump a wire or a screwdriver across the sending pin to the ground pin on the back of the gauge. If there is no ground pin, use a longer wire to jump the sending pin to the engine block. If the gauge goes to its lowest reading, it is functioning properly.

Check the Sender and Gauge:

If the gauge is working correctly, the issue may lie with the wire running to the sender or the sender itself. To check the wire, disconnect it from both the sender and the "S" pin on the back of the gauge. Set your multimeter to the Ohms scale and check the resistance within the wire. If there is no resistance (close to zero Ohms), the circuit is good, and the sender is likely faulty. In most cases, it is recommended to replace both the sender and the gauge to ensure accurate readings.

Inspect the Fuel Tank:

Once you have determined that the fuel gauge and sender are functioning correctly, it is important to inspect the fuel tank for any signs of damage or leaks. Ensure that the tank vent is clear and free-flowing. Also, check the fuel tank for any signs of corrosion or damage that may impact its performance. Refer to the previous section on how to pressure test a boat fuel tank for a comprehensive guide.

Check Fuel Level and Refill if Necessary:

Finally, check the fuel level in the tank and ensure it is at an appropriate level. If the tank is empty or low on fuel, refill it to the recommended level. This will help ensure that the fuel pump has sufficient fuel to operate effectively.

By following these steps, you can effectively check the fuel tank and gauge as part of troubleshooting fuel pump pressure problems in your outboard motor. Remember to refer to your owner's manual or seek professional assistance if you have any doubts or concerns during the process.

Examine the electrical system

Before you begin, ensure that the main electrical cutoff switch that governs motor ignition is turned off. Now, examine the electrical system, checking that all elements are in good condition. Look for any signs of corrosion or buildup on the connectors. Ensure that all fuses are intact and that the electrical system is functioning normally.

If you have an electric pump, you can do multimeter testing to examine its health. Take a multimeter with an amp clamp and turn the pump on. Then, place the amp clamp over the positive wire going to the fuel pump. Start the engine and record the amperage reading on the meter. If the reading does not match the manufacturer’s specifications, the pump will need to be replaced.

You can also get the voltage reading by placing the meter leads on the appropriate terminals. The sure sign of the pump’s failure is the presence of battery voltage in the meter.

If you suspect a problem with the electrical circuit, check the ground connections for the circulation pump. If voltage is present and the pump does not run, repair the connection or replace the vapor separator assembly.

Inspect the fuel system components

Inspecting the fuel system components is crucial to ensure the safe and efficient operation of your boat. Here are the steps you should take:

Check the Fuel Tank and Gauge: Confirm that there is enough fuel in the tank and that the gauge is functioning accurately. This step ensures that fuel supply is not the issue.

Inspect Hoses and Connections: Examine the hoses and connections from the tank to the fuel pump for any signs of damage, leaks, or restrictions. Look for stiff, cracked, worn, or damaged hoses, as these will need to be replaced. Pay special attention to the outboard's fuel line, which connects the outboard to the boat's fuel system.

Inspect the Fuel Filter: The fuel filter plays a critical role in preventing debris from reaching the fuel pump and other critical components. Check for clogged screens, loose fittings, or other damage that could lead to leaks or restrict fuel flow. Clean or replace the filter as necessary, following the manufacturer's guidelines.

Check the Fuel Primer Bulb: Ensure the fuel primer bulb is in good condition and functioning properly. If it shows any signs of cracks, leaks, or deformation, it should be replaced.

Inspect the Pulse Hose: The pulse hose connects the fuel pump to the intake manifold. Detach it and place a container underneath, then pull the starter rope several times. You should see fuel discharge from the hose. Lack of fuel discharge could indicate a problem with the fuel pump check valve or diaphragm.

Check the One-Way Valves: The one-way valves ensure the proper flow of fuel through the system. Detach the fuel pump, attach a pressure gauge to the outlet valve, and block the inlet valve with your thumb. Pump the pressure gauge and then release your thumb. If the pressure releases, it indicates that the inlet valve is faulty and needs replacement.

Examine the Diaphragm: The diaphragm is a rubber component inside the fuel pump that pushes the fuel through. Look for signs of damage, such as stalling, leaking, or fuel escaping into the water. You can test the diaphragm by clamping and tightening the pump with bolts and washers, attaching fuel lines to the inlet and outlet, and priming the bulb. If you see fuel leaking through the hole at the rear of the fuel pump, the diaphragm needs to be replaced.

By following these steps and inspecting the fuel system components, you can identify and address any issues that may impact the performance and longevity of your boat's fuel system.

Check for continuity

Checking for continuity is an important step in troubleshooting fuel pump issues. Here's a detailed guide on what it entails:

Fuel should flow smoothly from the tank to the pump. To check this, pump the primer bulb until it builds pressure. You will feel the bulb become firm, and this indicates that it is pressurised. Fuel should now travel from the tank to the pump, and you should see the outboard fuel filter fill up. This confirms uninterrupted flow.

If there is no fuel flow, or if the filter does not fill up, there may be an issue with the fuel pump or a blockage in the fuel system. Check the fuel lines and connections for any signs of damage or leaks. Also, ensure the fuel primer bulb is in good condition and free from cracks or deformities.

Listen for Pump Priming:

If your boat doesn't start, pay attention to any sounds coming from the fuel pump. Listen for the characteristic whirring sound of the fuel pump priming. This usually occurs for a few moments before the engine starts. If you have a dual-pump system, both pumps will prime. Turn the ignition to the "on" position and listen for the priming sound from the outboard motor. Repeat this process a few times to ensure it isn't a one-off issue. If the fuel pump has failed, you won't hear this distinctive sound.

Test the One-Way Valves:

The one-way valves are critical for delivering fuel through the system. They allow fuel to move in one direction, from the tank to the rest of the fuel system. These valves build up enough pressure to enable continuous fuel flow. Both the inlet and outlet valves are marked with arrows pointing towards the pump's centre.

To test their functionality, you'll need a pressure gauge:

• Detach the fuel pump from the engine.
• Attach the pressure gauge to the outlet valve.
• Block the inlet valve with your thumb.
• Pump the pressure gauge and then release your thumb.

If the pressure releases when you remove your thumb from the inlet valve, it indicates that the inlet valve is faulty. It is allowing pressure to escape in both directions, and the valves likely need replacement.

Examine the Diaphragm:

If the valve test is successful and the pressure holds, you can proceed to inspect the diaphragm. The diaphragm is a rubber component inside the fuel pump that pushes the fuel through. It is prone to issues like stalling, leaking, or allowing fuel to escape into the water.

To test the diaphragm, you'll need bolts, washers, and a hose clamp:

• Clamp and tighten the pump using the bolts and washers. Use the holes meant for attaching the fuel pump to the engine, and secure the washers on both ends.
• Attach one fuel line to the inlet and another to the outlet. Ensure both connections are clamped securely.
• Prime the bulb and observe the hole at the rear of the fuel pump, where you can see a portion of the diaphragm.

If you notice fuel leaking through this hole, your diaphragm is damaged and requires replacement.

By following these steps to check for continuity and perform related tests, you can effectively troubleshoot fuel pump issues in your outboard motor.

Listen for pump priming

If your boat doesn't start, stop and listen for the fuel pump priming. The fuel pump engages for a few moments before the engine starts. In a dual-pump system, both pumps will prime. Put the ignition in the "on" position and listen for a whirring sound from the outboard motor. Repeat the process a few times. If the fuel pump has failed, you won't hear the priming sound.

Listening for pump priming is a crucial step in troubleshooting fuel pump issues in outboard motors. It involves turning on the ignition and paying close attention to the distinct whirring or whining sound that indicates the fuel pump is engaging and priming. This process is essential because fuel pumps often fail unexpectedly, and the absence of this sound can be a telltale sign of a malfunctioning fuel pump.

To listen for pump priming, follow these steps:

• Turn the ignition to the "on" position: Start by turning the ignition key to the "on" position, but don't crank the engine. This initial step ensures that the electrical systems are activated, and the fuel pump receives power.
• Listen for the priming sound: Pay close attention and listen closely for a whirring, whining, or mechanical sound coming from the outboard motor. This sound indicates that the fuel pump is engaging and priming, preparing to deliver fuel to the engine.
• Repeat the process: It's important to repeat the process of turning the ignition on and off a few times to ensure that you accurately determine whether the priming sound is present or absent.
• Absence of priming sound indicates a potential issue: If you don't hear the priming sound, it could be a sign that the fuel pump has failed or is not receiving electrical power. This observation can be a crucial indicator that further diagnostics and troubleshooting are necessary.

Remember that the process of listening for pump priming is just one aspect of troubleshooting fuel pump issues in outboard motors. It is often followed by other tests, such as checking for electrical power to the fuel pumps, pressure testing, and inspecting other components like the VST/FSM assemblies and fuel filters. By following a comprehensive troubleshooting procedure, you can effectively identify and resolve fuel pump problems in your outboard motor.

Frequently asked questions