How to Tell If an Outboard Fuel Pump Has Gone Bad

No matter what make and model outboard engine you have, fuel pump problems will shut your boating plans down in a hurry. These problems can present themselves in a variety of ways. 

Outboard fuel pump gone bad

Outboard fuel pump problems can range from plain no-starts, to the motor running unevenly and sputtering, or even suddenly burning through fuel a lot quicker than before. But recognizing the problem and knowing how to test the fuel pump on your outboard can go a long way toward getting your boat back on the water. 

Buy outboard fuel system parts

Buy outboard fuel filters

How to Diagnose a Bad Fuel Pump on an Outboard

1. Do you hear the fuel pump? When you turn the key to start the engine, before you actually hear the engine you should hear the fuel pump spinning up. If you don’t, and the engine won’t start, it could be the fuel pump. On the other hand, it could be an electrical issue. 

2. Does your boat sputter or seem underpowered? This could be the fuel pump, but it could also be any point between the pump and the motor where fuel passes. Check the fuel lines for kinks and the fuel filter (or filters if your outboard has two) to make sure there are no clogs. 

3. Is your boat burning through fuel faster than normal? If you’ve had your boat a while, you probably have a good idea of how it burns through a tank of gas. So if you start feeling like you’re not getting the running time from your outboard that you’re used to, it could be a fuel system issue.

4. Is your outboard overheating? Fuel in the cylinders is an unwanted coolant. However, there are simpler explanations for why you’re seeing rising temps in your engine. Our video below on why an outboard overheats walks you through the troubleshooting process to rule out the fuel pump as the culprit.

Once you’ve ruled out other issues, do a compression test to make sure you don’t have an engine issue that looks (or sounds) like a fuel pump problem. Use a compression tester to see how much pressure the cylinders build when you turn the motor over. Remove a spark plug, then plug in the tester and turn the engine over to get a result. If the pressure is low, it means something is going on in the cylinder. When the pressure is okay (the reading will vary depending on the motor), that means you’re down to the fuel pump.

How to Test a Fuel Pump on an Outboard

To test the fuel pump, you’re going to first test the one-way valves, which only allow flow in one direction: from the tank to the engine. The inlet valve brings fuel into the pump, and the outlet valve allows fuel to flow from the pump on up to the engine. 

Outboard fuel pump testing

Fuel pumps typically have one inlet, but it may have two outlets. Testing them requires a pressure gauge and some hand tools to remove the pump.

Start by connecting the pressure gauge to the fuel outlet, and then seal the inlet with your thumb. Next, pump up the pressure gauge a few times and release your thumb. If the one-way valves are working properly, the pressure should hold because the valves shouldn’t allow pressure to escape backward (from outlet toward the inlet). However, if you see the pressure falling, one of the one-way valves is allowing pressure to move in the wrong direction. That’s a leak.

If the pump valves check out, and you have a mechanical pump with a diaphragm, you’ll test that next. The diaphragm pushes fuel through the pump, and on units that have them, you can see it through a hole in the back of the pump. Attach the fuel pump to the intake fuel line, clamp off the outlet fuel line, and squeeze the priming bulb to build pressure. If you see fuel leaking out of the hole, the diaphragm is bad.

How to Prevent Outboard Fuel Pump Problems

No matter how much care and maintenance you do, fuel pumps inevitably go bad. Yamaha recommends replacing them every three years on some of their motors, and many manufacturers offer fuel pump rebuild kits

To maintain a fuel pump, use a fuel stabilizer to minimize carbon deposits and prevent the fuel from going bad. If you’re winterizing your boat, fuel stabilizer is a must. But even in use, modern ethanol gas allows water droplets to mix in and create a sludge that can clog fuel lines, pumps and filters.

Watch the video above to see how to inspect, test and replace the fuel pump in a Yamaha F225 outboard.