Troubleshooting Boat Engines: Why Your Boat Loses Power

There are many reasons why a boat engine might lose power, and it can be frustrating to diagnose the issue. The most common cause is a lack of gas, but there are other likely options to explore. To operate properly, a boat engine needs a spark to ignite the air/fuel mixture. If the air or fuel is out of balance, or the spark is weak or improperly timed, the engine will run sporadically or not at all. Other potential issues include fouled spark plugs, a blocked fuel pump, a damaged airflow sensor, fuel line damage, low compression, a dirty carburetor, or a malfunctioning idle air control valve.

Faulty spark plugs and wires

Spark plugs can be fouled by fuel, oil, and/or carbon. This can cause the spark plug to fail to ignite the air-fuel mixture, resulting in the engine not starting. A fouled spark plug occurs when the plug isn't burning fuel normally, causing damage to the plug. A normal spark plug will appear dry with a grayish colour. A wet spark plug can indicate water in the fuel, while a white residue on the plug can mean the plug is too hot. If the plug is black with soot, it suggests that the fuel has too much oil. An eroded plug can also indicate a plug that is too hot.

To check for a faulty spark plug, inspect each spark plug for damage to the insulator tip, boot, and upper and lower insulators. If your plugs are fouled, use a rag to clean off any build-up. If there is a lot of build-up, you may need to use a knife or similar object to remove larger pieces. However, be careful not to damage the spark plug or change the spark plug gap. If the spark plugs are significantly fouled, replace them as soon as possible.

After checking the spark plugs, inspect the spark plug wires for any signs of aging, such as cracking or brittleness. Then, inspect the terminals and connection points. If there is any damage, corrosion, or breakage, you will need to replace the terminals. When installing new terminals, be sure to use the proper crimper to avoid creating a weak point in your electrical system.

Fuel pump issues

A boat engine, much like a car, truck, or SUV engine, requires three things to function properly: spark, fuel, and air. A weak or improperly timed spark, or an imbalance of fuel and air, can cause the engine to run sporadically or not at all. Fuel pump issues are a common cause of power loss in boat engines.

Fuel Pump Blockage

If your fuel pump is whining or squealing, it is likely due to one of two reasons. Firstly, the pump might be starving for fuel, which can occur when the fuel filter is blocked or clogged, preventing gas from reaching the pump. In this case, the issue is likely a blocked fuel filter rather than a faulty pump.

Fuel Pump Failure

The second reason for a whining or squealing fuel pump is that it is in the initial phase of failure. If you have changed your fuel filter and the problem persists, it is likely that the pump is failing and should be replaced as soon as possible.

Fuel Contamination

Corrosion, moisture, and debris can contaminate your fuel tank, and as these contaminants move through the fuel system, they can cause clogs and affect the fuel pump. Regular inspections and maintenance can help to identify and address these issues before they lead to pump failure.

Clogged Filters

Your boat's fuel filters are designed to prevent debris from reaching critical fuel system components. However, over time, these filters can become clogged, impacting fuel flow and resulting in performance issues. It is important to clean or replace fuel filters regularly to maintain optimal fuel flow and engine performance.

Electrical Faults

Fuel pumps rely on complex electrical components to function properly. Rusted connectors and melted wiring are common issues that can lead to fuel pump failure. Regular inspections and maintenance of the electrical system can help identify and address these issues before they cause pump failure.

Airflow sensor problems

A boat engine, much like a car engine, requires three things to operate properly: air, fuel, and a spark to ignite the air/fuel mixture. If the air or fuel is out of balance, the engine will run sporadically or not at all. A weak or improperly timed spark will have the same result. A dirty or damaged airflow sensor can cause a reduction in the performance of a fuel-injected marine engine.

A bad airflow sensor can cause hesitation, surging, poor fuel economy, poor performance, and difficulty starting the engine. A faulty sensor can report that less air is going into the engine than it actually is, leading to insufficient fuel delivery and causing the engine to surge. This can also result in higher fuel consumption, as the engine will be receiving too little or too much fuel.

To address a bad airflow sensor, you can try cleaning it first before opting to replace it. Cleaning the sensor involves unplugging and removing it, spraying a carb cleaner onto the wire inside, and letting it dry before reinstalling. If cleaning does not resolve the issue, you may need to replace the sensor.

It is important to perform regular maintenance on your boat engine to identify problems early and prevent unexpected issues while out on the water.

Fuel line damage

A damaged fuel line can cause a boat engine to lose power. Fuel lines are susceptible to deterioration, especially in older boats, and this can lead to stalling and poor engine performance.

The innards of older fuel hoses are highly vulnerable to alcohol deterioration. If left unchecked, the fuel lines can disintegrate, causing clogging, poor running, and even engine failure. The effects of this can be inconsistent, with some fuel lines deteriorating faster than others. Manufacturers generally use 10 years as the lifespan for gasoline hoses, but it is important to inspect the fuel lines every year and replace them if there is any sign of damage.

The EPA has introduced new fuel lines with a very tough inner liner that is impervious to alcohol-extended fuel. These lines are less flexible and more expensive, but they help to prevent the issues caused by alcohol deterioration.

If you don't have the option to invest in new lines, you can treat your ethanol fuel with a fuel stabilizer to prevent damage.

Carburetor issues

To fix this, the carburetor needs to be cleaned. This can be done by removing any debris or buildup with a rag or a knife, being careful not to damage the carburetor. If the carburetor is severely fouled, it may need to be replaced.

In addition to a dirty carburetor, a worn carburetor can also cause power loss. This is often caused by a worn shift linkage, which can contribute to stalling issues. In this case, the shift linkage may need to be replaced.

To prevent carburetor issues, regular maintenance is key. Boat owners should ensure that their boats are well-maintained, not just clean. This includes regularly checking and cleaning the carburetor and other engine components. By creating a checklist with a local dealer, boat owners can ensure they are doing everything necessary to keep their boat's engine running optimally and prevent unexpected breakdowns.

Frequently asked questions