Fuel Pump Failure: High-Pressure Pump Problems Explained

High-pressure fuel pumps are integral to the functioning of both petrol and diesel engines. However, they can malfunction or fail due to several reasons, such as mechanical damage, irregular maintenance, low-pressure system contamination, and faulty sensors. One of the first signs of a failing fuel pump is an increase in the engine's temperature, followed by issues like engine sputtering, power loss, noise in the fuel tank, and the car not starting. Diagnosing a faulty fuel pump is crucial to prevent serious damage and costly repairs.

Lack of maintenance

A high-pressure fuel pump is an indispensable part of a vehicle's fuel processing system. The pump is tasked with delivering fuel to the engine, making it one of the most important components in both petrol and diesel engines.

The main destroyer of high-pressure fuel pumps is a lack of maintenance. Specifically, a lack of oil changes can cause wear between the camshaft lobes and the high-pressure pump follower, preventing the pump from generating enough piston movement. Less movement of the pump means less pressure, and if the pressure is not correct, the fuel mixture could become too lean.

Before installing a new pump, it is imperative to examine the lobes on the camshaft. A lack-of-power complaint may improve, but it will never be completely corrected. Engine oil must meet OE specifications to prevent premature wear on the camshaft and high-pressure pump follower. Check with your engine oil supplier to see if an engine oil meets the OEM's specifications. Volkswagen, GM, and many other OEMs have oil standards that address wear issues on the camshaft and pump follower.

Additionally, neglected maintenance on diesel fuel filter housings can lead to issues. While manufacturers may claim that these can be left for longer, it is recommended to replace the fuel filter cartridge annually. Use good-quality filters, as poor-quality substitutes tend to fall apart, and the resultant fragments can damage the pump.

Faulty pressure and temperature sensors

When the fuel rail pressure sensor goes bad, the "Check Engine" warning light may illuminate on your dashboard. This doesn't always mean that the engine itself is bad, but rather something else in the vehicle is not allowing it to function properly. Other signs of a bad fuel pressure sensor include difficulty starting the engine, weak acceleration, and bad fuel mileage.

The fuel tank pressure sensor, on the other hand, is placed atop or inside the fuel tank and is responsible for identifying leaks in the fuel system, alerting you to a defective gas cap, signalling the engine computer that the evaporative emissions system is operating properly, regulating fuel consumption, and maintaining compliance with emissions regulations. If the fuel tank pressure sensor goes bad, the only sign will be the "Check Engine" light coming on. However, if your fuel system does have a pressure problem, you may also notice an increase in fuel consumption, a loss of power and acceleration, black smoke coming from the tailpipe, or gasoline dripping from the tailpipe.

Old calibrations

As engineers maximise the energy output from every fuel droplet, every element in the system operates on a knife-edge of driveability. Sometimes, they get it wrong, and they don't find out until a direct-injection system is in the field and racking up warranty claims.

There is a direct relationship between pump pressures, camshaft position, and pressure solenoid position. These elements, along with injector pulses, can be calibrated to give the best performance and component life.

If you are diagnosing a driveability problem on a direct-injection vehicle or replacing a high-pressure pump, make sure the ECU has the latest calibration. Newer calibrations can help solve wear problems and driveability issues and may save you from replacing the pump.

Fuel pump pressure solenoid

A high-pressure fuel pump is typically driven by a camshaft. A lobe on the camshaft pushes a follower or roller that moves a piston. The piston in the pump has two cycles: suction and compression. The solenoid on the side of the pump controls how much fuel is compressed during the compression stroke.

During the suction cycle, the solenoid allows fuel from the low-pressure side of the fuel system to enter the pump. As the piston starts to travel upwards, the solenoid remains open. The fuel is pushed into the low-pressure side of the fuel system when the solenoid is open. When the solenoid is shut, the low-pressure and high-pressure sides of the fuel system are isolated.

The length of time the solenoid is open determines how much fuel reaches the fuel injectors. If there is low demand on the engine, the solenoid will remain open longer, and a smaller volume of fuel is compressed. If there is a high demand on the engine, the solenoid will close sooner, and a higher volume of fuel will be compressed.

The operation of the solenoid is engine-position-dependent. The ECU and pump use the camshaft position sensor to know the position of the pump's lobe on the camshaft. With engine position information, it can accurately time the events of the solenoid on the high-pressure fuel pump.

If you suspect that your high-pressure fuel pump is failing, you can test it by performing a visual inspection and checking for any leaks around the fuel pump. You can also use a vehicle diagnostic tool such as an OBD2 scanner to check the error memory and identify any fault codes related to the fuel pump.

Ignoring the signs

Engine Damage: A failing fuel pump can starve your engine of necessary fuel, leading to poor performance, stalling, and, in extreme cases, engine damage. The lack of sufficient fuel can cause the engine to run lean, resulting in increased wear and tear. In addition, a faulty fuel pump may cause the engine to overheat, which can also lead to serious engine damage.

Catalyst Harm: When a direct-injection engine with a high-pressure pump issue goes into limp or low-pressure mode, the catalyst could be harmed. This mode is activated to prevent damage to the engine, but it can have negative consequences for the catalyst.

Reduced Performance: A failing fuel pump may cause your vehicle to lose power, especially when accelerating or driving uphill. This is due to the inability of the fuel pump to keep up with the engine's fuel demands at higher speeds or under heavy loads. You may experience misfiring, stuttering, or an inability to reach or maintain high speeds.

Unsafe Driving Conditions: Ignoring the signs of a failing fuel pump can create unsafe driving conditions. Your vehicle may surge forward or lose power unexpectedly, making it difficult to maintain control of the vehicle and potentially leading to accidents.

Increased Fuel Consumption: A faulty fuel pump may inject too much fuel into the engine, resulting in poor fuel efficiency. This will lead to more frequent trips to the gas station and higher fuel costs.

Emission Standards Failure: A malfunctioning fuel pump can cause the engine to run rich, which means there is too much fuel relative to air. This can lead to higher levels of harmful emissions and potentially cause your vehicle to fail emissions tests.

In conclusion, it is essential to pay attention to any warning signs your vehicle may be exhibiting. Regular maintenance and prompt attention to potential problems are crucial in preventing major issues and ensuring the safety and reliability of your vehicle.

Frequently asked questions