Checking Fuel Pressure: A Guide For Harley Owners

Checking the fuel pressure on a Harley motorcycle is a common troubleshooting step when experiencing performance issues. The ideal fuel pressure for a Harley is between 55-62 PSI. To check the fuel pressure, you will need a fuel pressure gauge that fits a Chevy system. The test port is located on the right side of the bike, between the cylinders, near the bottom of the throttle body. You can then screw on the test gauge, turn on the ignition, and check if the system comes up to pressure when the fuel pump runs. If the fuel pump is running continuously, this could indicate an electrical issue. Other potential causes of low fuel pressure include a faulty fuel pump, a restricted pressure line, or a leak inside the tank.

Harley fuel pressure gauge test port location

To check the fuel pressure on your Harley, you will need to purchase, rent, or borrow a quality Harley fuel pressure tester gauge with the correct adapters to fit your Harley-Davidson output fittings.

The fuel pressure gauge test port is located on the right side of the bike, between the cylinders, near the bottom of the throttle body. It resembles a tire valve stem with a cap on it. You will need to screw on the test gauge, turn on the ignition, and listen for the fuel pump to run. Once the system comes up to pressure, start the bike and see if it maintains pressure. The pressure should be somewhere between 55 and 62 psi.

To perform a correct fuel pressure test, you should also have your factory service manual nearby when diagnosing a failing fuel system. It is also recommended to remove your fuel pump fuse and run the motorcycle until it stalls before beginning the test. This will diminish or eliminate the fuel pressure in the system, allowing you to safely unplug the fuel delivery line from the fuel tank.

Additionally, before disconnecting the fuel line, it is advisable to spray it with a light penetrating oil to help work past any corrosion in the fitting and prevent damage to the O-ring inside the tank fitting.

Harley fuel pump failure signs

Harley-Davidson motorcycles are renowned for their performance and distinctive style. However, even these iconic machines can encounter issues, and a failing fuel pump is one of the most common problems. Here are some instructive signs to watch out for that may indicate a faulty fuel pump:

Harley Sputtering Engine

High-speed riding can cause the engine to sputter when the fuel pump is malfunctioning. This happens when the fuel pump fails to deliver a consistent flow of fuel to the engine at the correct pressure. If you notice sputtering, it's advisable to have the fuel pump checked by a technician.

Surging

A faulty fuel pump can cause your bike to surge unexpectedly when riding at a steady speed. This is due to erratic resistance within the fuel pump motor, which can be dangerous, especially at high speeds. If you experience this, it's best to start looking for a replacement fuel pump immediately.

Reduced Mileage

Keep an eye on your fuel consumption. If you notice that your bike is using more fuel to travel the same distance, it could indicate an issue with the fuel pump's relief valve, allowing more fuel into the engine than necessary. As this issue can be challenging to detect, regularly monitoring your fuel usage is essential.

Engine Failing to Start

One of the earliest signs of a failing fuel pump is when the engine won't start due to insufficient fuel supply. This could be a result of the fuel pump losing its ability to provide enough fuel to the engine, making it difficult to start.

Stalling

Frequent stalling while riding could be a sign of a dirty or blocked fuel pump. As the blockage worsens, the fuel supply becomes more erratic, leading to increased stalling, especially during acceleration. In this case, you may need to replace the fuel filter along with the fuel pump.

Poor Engine Performance

A faulty fuel pump can cause the engine to surge, stumble, or hesitate when operating under solid loads, such as accelerating or riding uphill. While there may be no noticeable symptoms during regular riding conditions, the engine may struggle to access the extra fuel required for acceleration or riding up an incline.

To check for fuel pump issues, you can refer to your Harley's service manual for the proper procedure. Alternatively, you can visually inspect the fuel pump and its components, such as the filter and lines, for any blockages or damage. Remember, timely intervention by a professional or a knowledgeable DIY enthusiast can ensure that your Harley-Davidson continues to provide a smooth and enjoyable riding experience.

Harley fuel pressure regulator failure signs

A faulty fuel pressure regulator can cause a range of issues with your Harley. Here are some signs that your fuel pressure regulator is failing:

• Engine Performance Problems: A bad fuel pressure regulator can cause a loss of fuel pressure, leading to hard-starting, rough running, stalling, and a lack of power.
• Check Engine Light: If the fuel pressure becomes too high or too low due to a faulty regulator, it will likely trigger the check engine light on your dashboard.
• Black Smoke from the Exhaust: A faulty regulator can cause the engine to run rich, resulting in black smoke from the exhaust.
• Fuel Leakage: A damaged fuel regulator diaphragm or outer seal can cause fuel leakage, leading to performance issues and unpleasant smells.
• Misfiring Engine: One of the most common signs of a bad fuel pressure regulator is an engine that misfires during idle or acceleration. You may hear sputtering or other unusual sounds.
• Loss in Acceleration: An incorrect fuel pressure will cause the air-fuel ratio to be too rich or too lean, resulting in a drop in acceleration and a decrease in engine performance.
• Vacuum Hose Filled with Gasoline: A ruptured diaphragm in the regulator can cause fuel to enter the vacuum system instead of the engine, filling the vacuum hoses and intake manifold with gasoline.
• Gasoline Smell from the Dipstick: A faulty regulator can cause the engine to run rich, leading to unburned fuel flowing into the oil pan and filling it with gasoline. This will be noticeable when checking the engine oil dipstick.

Harley fuel pressure troubleshooting

Step 1: Identify the problem

Fuel pressure issues can be caused by various factors, such as a faulty fuel pump, clogged fuel lines, or a malfunctioning pressure regulator. Common signs of fuel pressure problems include difficulty starting the engine, loss of power, and irregular idle.

Step 2: Check fuel pressure

To check the fuel pressure on your Harley, you will need a fuel pressure gauge. You can purchase or rent one from an auto parts store. Locate the fuel pressure test port, which is usually on the right side of the bike, between the cylinders, near the bottom of the throttle body. It resembles a tire valve stem with a cap. Screw on the test gauge, turn on the ignition, and listen for the fuel pump to run. Observe if the system reaches the desired pressure. Then, start the bike and check if the pressure is maintained. For Harley bikes, the fuel pressure should typically be between 55 and 62 PSI.

Step 3: Troubleshooting

If the fuel pressure is low, there may be a restriction in the fuel filter or pump, a leak in the fuel lines, or a faulty pressure regulator. Check for leaks in the fuel lines, especially the corrugated hose coming out of the tank, which is prone to developing pinhole leaks. Ensure that the fuel pump is functioning properly and producing adequate flow. If the pressure is high, inspect the check valve fitting and the fuel pressure regulator.

Step 4: Take corrective actions

Depending on the issue identified, take the necessary corrective actions. For example, if the fuel filter is clogged, replace it with a new one. If the fuel pump is faulty, have it repaired or replaced. Ensure that all fuel lines and connections are secure and free from leaks. If the pressure regulator is malfunctioning, it may need to be adjusted or replaced.

Step 5: Test and verify

After making the necessary repairs or adjustments, retest the fuel pressure to ensure that it is within the specified range. Start the bike and observe its performance. If the fuel pressure is stable and within the desired range, the issue should be resolved. Take the bike for a test ride to confirm that it is running smoothly and responding well to throttle input.

Harley fuel pressure testing tools

Checking the fuel pressure on your Harley is a relatively simple task, but it does require the right tools. Here are some Harley fuel pressure testing tools and methods to help you get the job done.

Fuel Pressure Gauge

One of the most common tools used to check fuel pressure on a Harley is a fuel pressure gauge. This tool allows you to measure the pressure in the fuel system and diagnose any potential issues. You can find fuel pressure gauges at most auto parts stores or online. When purchasing a fuel pressure gauge, look for one that fits a Chevy system, as these tend to work well with Harleys.

Adapter or Fitting

In order to attach the fuel pressure gauge to your Harley, you may need an adapter or fitting. The fuel rail on your Harley may not have a port that is compatible with the gauge, so you'll need to find an adapter that fits. Some people choose to replace the banjo bolt on the fuel rail with one that has a fitting for the pressure gauge. This can be a simple and effective solution.

CTA Tools Fuel Injection Tester

If you're looking for a more comprehensive testing tool, the CTA Tools 3425 Fuel Injection Tester is a good option. This tool is designed for non-Bosch and GM TBI systems, and it includes the necessary connectors to plug directly into your Harley. It's also relatively affordable compared to some other specialty tools on the market.

Feuling Pressure Relief PSI Testing Tool

Another option specifically designed for Harley-Davidson Twin Cam engines is the Feuling 9010 Pressure Relief PSI Testing Tool. This professional-grade tool allows you to bench test the cam plate before installation and set the spring pressure to the desired pop-off psi. It includes a regulator, a 0-100 psi pressure gauge, a gasket, and the necessary hardware.

DIY Methods

If you're handy and want to save some money, there are some DIY methods you can try. One option is to create your own adapter by purchasing the tank-to-rail hose from the dealer and using barbed fittings from a hardware store. Another method is to use a "T" fitting to run a gauge and operate the engine simultaneously. This can be a more affordable option, but it may not be as accurate as some of the other tools mentioned.

Remember to always refer to your Harley's service manual for specific fuel pressure values and recommendations. By using the right tools and methods, you can accurately check the fuel pressure on your Harley and ensure it's running optimally.

Frequently asked questions