Diagnosing High-Pressure Fuel Pumps: A Step-By-Step Guide

High-pressure fuel pumps are an essential part of modern fuel systems, especially in diesel engines. They are also used in petrol engines with direct injection. To check a high-pressure fuel pump, you can either physically measure the fuel pressure with a test port on the fuel rail or monitor it electronically with a scan tool. If the pump is mechanical, testing it may require removing it from the vehicle and conducting a bench test.

There are various signs that indicate a defective high-pressure pump, including erratic engine running, poor starting behaviour, and the engine stopping with the warning light coming on. Before installing a new pump, it is important to check the pump drive, roller tappets, and camshaft for damage and proper functioning, replacing any defective parts.

Check for erratic engine running

A faulty high-pressure fuel pump can cause erratic engine running. To check for erratic engine running, you can look out for the following signs:

• The engine will feel rough and bouncy.
• The car feels extra shaky when stationary, for example, at a stoplight.
• The engine will run slower or idle below normal.
• The needle on your odometer bounces up and down and behaves erratically, instead of staying steady below 800 RPM.
• The RPMs are inconsistent.
• The check engine light or engine service light illuminates.

If you notice any of these signs, it is important to get your car checked out as soon as possible to prevent small problems from becoming large and expensive issues.

In addition to erratic engine running, other signs of a faulty high-pressure fuel pump include:

• No power in the upper speed range.
• Poor starting behaviour.
• The engine stops and the engine warning light comes on.

Check for a lack of power in the upper speed range

Checking for a lack of power in the upper speed range can indicate a defective high-pressure pump. This can be caused by severe mechanical strain, high fuel pressures, a lack of lubricant, and temperature differences. These factors promote wear and can lead to a defect in the high-pressure pump over time.

To check for a lack of power, you can perform a fuel pump pressure test. This test will help you determine if the fuel pump is operating within the specified range and identify any potential problems. Here are the steps to follow:

• Locate the fuel pump test point: The test point is typically located near the fuel injectors. Check your vehicle’s manual or consult a repair guide for the exact location.
• Warm up the engine: Start the engine and let it reach normal operating temperature. This ensures accurate pressure readings.
• Connect the fuel pressure gauge: Attach the fuel pressure gauge to the fuel pump test point and ensure a secure connection.
• Check the pressure at idle speed: With the engine running at idle speed, observe the fuel pressure reading on the gauge. Refer to the pump specifications to determine the recommended pressure range.
• Check the pressure at rated speed: Increase the engine speed to the rated speed specified for your pump. Note the fuel pressure reading and compare it to the specified range.

If the fuel pressure readings are within the specified range, your fuel pump is functioning properly. However, if the pressure is outside the specified range, it may indicate a problem with the fuel pump or other components of the fuel system. In such cases, further diagnostics and investigation are necessary to identify and address the issue.

Additionally, you can check for other symptoms of a defective high-pressure pump, such as erratic engine running, poor starting behaviour, and the engine stopping unexpectedly with the engine warning light coming on.

Check for poor starting behaviour

Poor starting behaviour is one of the most common symptoms of a failing high-pressure fuel pump. If your engine struggles to start or doesn't start at all, it could be due to a faulty fuel pump that is unable to deliver the required amount of fuel to the engine. This can result in the engine cranking for an extended period before eventually turning over or, in some cases, failing to start altogether.

When you attempt to start your vehicle, the fuel pump should supply pressurised fuel to the engine. If the pump is faulty or weak, it may not be able to deliver the necessary fuel pressure, leading to poor starting behaviour. This can be particularly noticeable when the engine is cold or when trying to start the vehicle after it has been sitting for an extended period.

In addition to starting issues, a failing high-pressure fuel pump can also cause problems while driving. You may experience a loss of power, decreased performance, engine stalling, or poor fuel efficiency. The vehicle may struggle to maintain speed or accelerate as expected, especially when driving uphill or under heavy load.

If you suspect a faulty high-pressure fuel pump, it is recommended to consult a qualified mechanic or automotive specialist. They can perform a thorough inspection and run diagnostic tests to determine the root cause of the issue. A visual inspection can be done to check for any leaks around the fuel pump, and more advanced testing can be done using a vehicle diagnostic tool to read error codes and assess system parameters.

Check for engine stopping and the engine warning light coming on

If your engine stops and the engine warning light comes on, it could be a sign of a faulty high-pressure fuel pump. However, there are several other reasons why this might happen, so it's important to get a proper diagnosis.

The high-pressure fuel pump is an essential component of modern engines, delivering fuel from the tank to the engine. When it malfunctions, it can cause a range of issues, from engine stalling to complete engine failure.

If your engine stops and the warning light comes on, it's important to get your car checked by a professional mechanic as soon as possible. They will be able to diagnose the issue and determine if the high-pressure fuel pump needs to be replaced.

• Atypical fuel tank noises, such as whining sounds
• Engine struggles to start or doesn't start at all
• Power loss and decreased performance, especially when driving uphill or under heavy loads
• Poor fuel efficiency
• Engine stalls or hesitates, especially during cold starts
• Check engine light is on and trouble codes related to the high-pressure fuel pump are stored in the vehicle's computer

If you notice any of these symptoms, it's best to take your vehicle to a mechanic for further diagnosis and repair.

Check for external mechanical damage

Checking for external mechanical damage on a high-pressure fuel pump is an important step in diagnosing and resolving issues with your vehicle's fuel system. Here are some detailed instructions and considerations to guide you through the process:

• Visual Inspection: Begin by performing a thorough visual inspection of the high-pressure fuel pump and its surrounding components. Look for any signs of physical damage, such as dents, cracks, leaks, or loose connections. Pay close attention to the pump's exterior housing, fuel lines, connections, and nearby engine components.
• Fuel Lines and Connections: Inspect the fuel lines and connections associated with the high-pressure fuel pump. Ensure that the lines are securely connected and free from damage, such as cracks, kinks, or leaks. Fuel line issues can lead to fuel leaks, restricted fuel flow, or even contamination. If you notice any damage or degradation, replace the affected fuel lines with reinforced rubber fuel hoses.
• Mounting and Bolts: Check the mounting bolts of the high-pressure fuel pump for proper tightening. Loose mounting bolts can lead to oil leaks and potential damage to surrounding components. Use a torque wrench to ensure that the bolts are tightened to the manufacturer's specifications, typically within a range of 25 to 35 foot-pounds. Apply a small amount of thread-locking compound before reassembling to ensure the bolts remain secure.
• Diaphragm and Seals: Inspect the diaphragm and seals within the high-pressure fuel pump for any signs of damage or leaks. The diaphragm is critical to maintaining the correct fuel pressure and ensuring a smooth fuel flow. Leaks in the diaphragm can cause fuel to escape, leading to poor engine performance or, in severe cases, the risk of an explosion. Also, check the seal between the diaphragm and the two halves of the pump body for integrity.
• Cam and Operating Lever: Examine the cam and operating lever for signs of wear or damage. The cam and lever play a crucial role in the mechanical operation of the fuel pump. Signs of wear may include scratches, pitting, or uneven surfaces. If the cam or lever is damaged, it can affect the pump's ability to deliver fuel at the required pressure and volume.
• Gaskets and Fuel Pipes: Inspect the gaskets and fuel pipes for leaks or damage. Gaskets provide a tight seal between the pump and the engine, and damaged or worn gaskets can lead to fuel or oil leaks. Similarly, loose or damaged fuel pipes can result in leaks, restricting fuel flow to the engine. Replace any faulty gaskets or fuel pipes to maintain the integrity of the fuel system.

Remember, safety should be a top priority when working on any vehicle, especially when dealing with fuel systems. Always refer to the vehicle's repair manual, wear appropriate protective gear, and ensure the engine is turned off and has cooled down before beginning any inspection or repair work.

Frequently asked questions