Testing A High-Pressure Diesel Fuel Pump: Step-By-Step Guide

Testing a high-pressure diesel fuel pump requires a specialised diagnostic approach. The modern High-Pressure Common-Rail (HPCR) fuel system is a far cry from the old-school conventional (mechanical) diesel fuel injection systems. The HPCR system operates at extreme pressures and demands precise settings to achieve optimal efficiency. To test such a system, you'll need to employ special diagnostic tools to identify faults. Before replacing diesel injectors or pumps, it's advisable to conduct additional checks to confirm the diagnosis. This includes assessing injector leak back and imbalance, high-pressure pump results, and the performance of low-pressure or vacuum supply lines and primer pumps.

Check for a test port on the fuel rail

To check for a test port on the fuel rail, you'll need to locate the fuel pump test point, which is usually near the fuel injectors. Consult your owner's manual for specific instructions, as the location of the fuel pump varies from vehicle to vehicle. Once you've located the fuel pump test point, look for a separation joint or a test port where you can attach the pressure gauge.

Some cars are designed with a convenient pressure port on the engine fuel rail, where you can simply remove the cap and attach the gauge. If your car doesn't have this feature, you may need an adapter from the test kit, which can be attached at the fuel filter or fuel pressure feed line leading to the engine's fuel rail.

When attaching the pressure gauge, keep in mind that a small amount of fuel may be present, so have a shop towel ready to wipe up any spills. It's also important to work in a well-ventilated area and avoid any open flames or sparks during the testing process.

Monitor electronically with a scantool

Monitoring electronically with a scantool is a modern method of testing a high-pressure diesel fuel pump. This method is more efficient and accurate than traditional analog and hands-on diagnostic procedures, which often involved a pressure gauge and voltmeter. The scantool can be used to verify if the modules controlling the fuel pump are receiving the correct data, such as oil pressure, crank position, and security information. It can also be used to monitor data shared between modules, such as fuel level and EVAP system status.

To begin the diagnostic process, a visual inspection of the vehicle is necessary. This is followed by verifying the customer's complaint to ensure that the correct issue is being addressed. The next step is to connect the scan tool and pull the codes to ensure the modules are communicating on their respective buses. Low-end generic tools may not be able to communicate with all modules, so an enhanced or factory scan tool is recommended. These enhanced scan tools can often perform a "health check" with the press of a button, pulling codes and parameters from the vehicle's modules.

After gathering the necessary data, the technician can develop diagnostic strategies and further tests to resolve any issues. Every fuel system has specific parameters that must be met for the pump to be energised, such as a crank sensor signal and oil pressure readings. It is important to address any "loss of communication" codes that may be present, as these can often be indicative of a larger issue that could result in a no-start condition.

Factory and enhanced scan tools are capable of monitoring pressure transducers on both the high and low sides of the system. This data can be used to assess the health of the fuel pumps and perform various diagnostic tests, such as cylinder balance tests. The pressure transducers can also aid in diagnosing hard-start problems. By performing these diagnostics from the driver's seat, technicians can increase their productivity and accuracy, resulting in a more profitable department.

Check the fuel pressure

Checking the fuel pressure is a crucial aspect of testing a high-pressure diesel fuel pump. Here is a detailed guide on how to go about it:

Step 1: Safety Precautions

Before initiating any diagnostic tests, it is imperative to prioritize safety. Ensure you are wearing protective gear, such as safety goggles and gloves. Work in a well-ventilated area, and refrain from smoking or introducing any potential ignition sources. These precautions are crucial because releasing fuel from a pressurized system can pose fire hazards and safety risks.

Step 2: Start the Engine and Install a Fuel Pressure Gauge

Turn on the engine and let it idle. Install a fuel pressure gauge by connecting it to the test port on the fuel rail. This gauge will allow you to monitor the fuel pressure and make accurate measurements.

Step 3: Run the Pump and Record the Pressure Reading

With the engine running, activate the fuel pump and carefully observe the pressure indicated on the gauge. Make sure to take note of the pressure reading.

Step 4: Compare the Reading to the Manufacturer's Specification

After obtaining the pressure reading, compare it to the specifications provided by the manufacturer. This comparison will help you determine if the pressure is within the acceptable range. If the pressure falls below the specified value, it indicates an issue that needs to be addressed.

Step 5: Perform a Fuel Volume Test (Optional)

If the fuel pump is supplying sufficient pressure, you can optionally perform a fuel volume test to ensure that the correct amount of fuel is being delivered to the fuel injectors. This test provides additional assurance that the fuel system is functioning properly.

Step 6: Use a Flowmeter or a Glass Measuring Container for Fuel Delivery Test

For accurate measurement of fuel delivery, it is recommended to use a flowmeter if one is available. Alternatively, a reliable method is to use a glass measuring container, as fuel can corrode or fog up plastic. Start the engine and collect a fuel sample for a specified duration (e.g., five seconds) with the pump running. Refer to the manufacturer's specifications to determine the expected fuel volume within the given timeframe.

Step 7: Convert Units and Make Comparisons

You might need to convert the measured values (e.g., milliliters per second) to the corresponding units specified by the manufacturer (e.g., gallons per hour) for comparison. This ensures that your measurements align with the standard units used by the manufacturer.

By carefully following these steps and comparing your readings to the manufacturer's specifications, you can effectively check the fuel pressure and volume in a high-pressure diesel fuel pump system. Remember to prioritize safety and accuracy throughout the testing process.

Test fuel delivery with a flowmeter or glass container

Testing the fuel delivery with a flowmeter or glass container is a straightforward process. Firstly, ensure you are wearing safety gear, including gloves and safety glasses, and that you are working in a well-ventilated area. This is because releasing fuel under pressure can cause fires and injuries, so safety is paramount.

Next, start the car and let it idle. You will then need to collect a fuel sample for five seconds with the pump running. The pump should deliver a specific amount of fuel within this time frame, which you can check by referring to the manufacturer's specifications. You may need to convert milliliters per second to gallons per hour to make this comparison. This test will determine whether the correct amount of fuel is being delivered to the fuel injectors.

Glass is a good choice of container for collecting the fuel sample, as fuel can corrode or fog up plastic.

Perform a load test

To perform a load test on a high-pressure diesel fuel pump, you will need to check the fuel pressure. Start by starting the car and letting it idle. Install a fuel pressure gauge and run the pump, noting the pressure reading. Compare this reading to the manufacturer's specifications. If the pressure is low, you will need to address this issue.

If the fuel pump is supplying sufficient pressure, you can then perform a fuel volume test to determine if the correct amount of fuel is being delivered to the fuel injectors. This can be done using a flowmeter, which is the most accurate method. However, if you don't have access to a flowmeter, you can perform a timed fuel delivery test using a glass measuring container. Start the car and let it idle, then collect a fuel sample for five seconds with the pump running. The pump should deliver a specific amount of fuel within this time frame, which can be found in the manufacturer's specifications.

It is important to note that before performing any diagnostic tests, you should prioritise safety. Releasing fuel under pressure can cause fires and injuries, so be sure to wear safety glasses and gloves, work in a well-ventilated area, and avoid smoking or having anything around that could cause a spark.

Frequently asked questions