Fuel Pressure Issues: Causes And Solutions

High fuel pressure can cause both short-term and long-term damage to vehicles. It can lead to an engine being overfuelled, resulting in poor fuel economy, black smoke from the exhaust, and poor engine performance. A kink in the fuel return line can cause higher-than-normal fuel pressure, as can a bad fuel regulator or a clogged return line. Checking fuel pressure is an important part of troubleshooting the overall fuel injector system.

Faulty fuel pressure regulator

A faulty fuel pressure regulator can cause a range of issues with your vehicle's performance and, in some cases, even safety hazards. Here are some common problems that can be caused by a faulty fuel pressure regulator:

Engine Performance Problems

A faulty fuel pressure regulator can cause a loss of fuel pressure, resulting in hard-starting, rough running, stalling, and a lack of power. The engine may misfire, and there could be a decrease in fuel efficiency and acceleration. These issues are often due to the interruption of the vehicle's fuel pressure, which throws off the engine's air-fuel ratio and tuning.

Check Engine Light Illuminated

The check engine light may come on as your car's engine computer detects issues that could lead to increased emissions. This is usually accompanied by the storage of a corresponding diagnostic trouble code (DTC) in the device's memory.

Black Smoke from the Tailpipe

A faulty fuel pressure regulator can cause the engine to run rich, resulting in black smoke emitting from the exhaust system. This is due to an excessive amount of fuel being forced through the injectors, producing increased emissions and black sooty exhaust.

Fuel Leaks

If the diaphragm or seals of the fuel pressure regulator fail, fuel leaks can occur. This not only impacts vehicle performance but also poses a potential safety hazard. Fuel leaks often result in a noticeable fuel smell and, in some cases, may be visible from the tailpipe.

Noise from the Fuel Pump

While a properly functioning fuel pump typically makes a quiet humming sound, a faulty fuel pressure regulator can cause the pump to become noisier, which can be irritating, especially in slow-moving traffic.

Cost of Replacement

The cost of replacing a fuel pressure regulator can vary depending on the vehicle and the type of regulator. In the UAE, for example, the equipment cost ranges from AED 110 to AED 150, while the labour cost for replacement can range from $250 to $400 in other markets.

Obstructed return lines

An obstructed fuel return line can cause a range of issues, from poor engine performance to safety hazards. The fuel return line is responsible for routing excess fuel from the engine back to the fuel tank. If this line becomes obstructed, it can lead to a build-up of pressure in the fuel system, resulting in higher than normal fuel pressure readings.

One of the most common signs of an obstructed fuel return line is fuel leaks. A puncture or wear in the fuel return hose can cause fuel to accumulate under the car, creating a strong fuel odour and an increased risk of fire. Even a small spark could ignite the leaking fuel, leading to a dangerous situation.

Another issue that may arise from an obstructed fuel return line is vapor lock. This occurs when fuel turns into gas due to heating up from close exposure to the engine. Vapor lock is often accompanied by performance problems such as engine misfires, poor acceleration, and reduced fuel efficiency.

An obstruction in the fuel return line can also cause the engine to flood with fuel, leading to potential damage to the fuel pump and other components. In some cases, the excess fuel may be dumped into the cylinders, causing further issues.

To diagnose an obstructed fuel return line, it is recommended to remove the hose and check for any blockages by blowing air through it or pouring a cleaning solution. If the line is damaged or clogged, it should be replaced to ensure the proper functioning of the fuel system and to prevent potential safety hazards.

It is important to note that fuel injection systems may or may not have return lines. Mechanical diesel fuel systems with an injector pump always have a return line, while electronic diesel systems may vary.

Fuel rail pressure sensor

A fuel rail pressure sensor is an electronic device that monitors the pressure inside the fuel rail, the metal tube that connects the fuel delivery system to the engine. It helps the powertrain control module (PCM) control the fuel supply to the engine. The fuel rail pressure sensor is usually found mounted on the fuel rail.

A faulty fuel rail pressure sensor can cause several issues, including:

• An illuminated check engine light: The check engine light comes on if the ECM algorithms detect any sensor input that is out of range. A bad fuel pressure sensor will disrupt the fuel supply, preventing the engine from getting the gasoline it needs and leading to hard starts, no starts, or loss of power.
• Engine start problems: When starting your car, the PCM orders the fuel delivery system to surge a batch of fuel to the engine. If the fuel rail pressure sensor is faulty, it can affect the amount of fuel delivered to the engine, causing start problems.
• Poor engine performance: The fuel rail pressure sensor provides feedback to the ECM on the amount of pressure in the rail. If the engine doesn't receive enough fuel, it will run lean, burning a lean mixture that will wear out the engine faster and increase NOx emissions. Conversely, if the sensor fails, the engine may get more fuel than it needs, resulting in lower fuel economy.
• Engine misfires and rough running: An erratic fuel rail pressure sensor can provide the wrong information to the PCM, leading to an incorrect air-fuel mixture. If the engine runs rich, it can experience knocking or run rough, potentially damaging the engine. Running lean may cause the engine to die or run with very low power.

It is possible to drive with a faulty fuel rail pressure sensor in an emergency for a short time, but running lean or rich will likely cause more serious engine problems in the future. Therefore, it is recommended to replace the worn-out or failed sensor as soon as possible. The cost of a replacement fuel rail pressure sensor typically ranges from $60 to $210, depending on the vehicle's details and the product's brand.

Fuel rail relief valve

A fuel rail relief valve, also known as a pressure relief valve, is a critical component of a common rail fuel system. It is a relatively simple valve located on the fuel rail before the injectors and after the injection pump. Its main function is to regulate fuel rail pressure before the fuel reaches the injectors.

The fuel rail relief valve acts as a wastegate or bypass, returning excess fuel pressure back into the fuel system. This is important because it helps prevent high fuel pressure, which can lead to a rich air-fuel ratio and increased emissions. Excessive hydrocarbons from high fuel pressure can also overheat and damage the catalytic converter.

The fuel rail relief valve is designed to open at a specified fuel pressure limit, relieving excess fuel back to the tank. This maintains a constant pressure to the injectors, improving fuel efficiency. A faulty fuel rail relief valve can lead to hard starts, lack of power, and poor fuel economy. It may also cause the engine to run rich, resulting in increased emissions and potential damage to the catalytic converter.

One of the most common issues with fuel rail relief valves is a weak or blown valve, which can be caused by an internal spring that fatigues and allows fuel to bypass before necessary. This can lead to a hard start or no-start situation as the engine may not be able to build enough rail pressure to fire. A leaking valve can also cause decreased fuel efficiency and black smoke from the exhaust system.

To diagnose a faulty fuel rail relief valve, you can remove the return line located on top of the valve and crank the engine. If there is fuel present, especially if it is trickling out at startup pressure, the valve needs to be replaced. Proper maintenance, including regular replacement of the fuel filter and draining of the water separator, can help prevent issues with the fuel rail relief valve and other engine components.

High-pressure fuel pump

A high-pressure fuel pump is a critical component of a direct-injected engine. It is responsible for delivering highly pressurised fuel directly to each cylinder's combustion chamber. This type of pump is typically driven by the engine's camshaft and is located under the bonnet, unlike the lower-pressure fuel pump found in the fuel tank of older cars.

The high-pressure fuel pump's function is to create sufficient pressure so that the fuel atomises completely. This process results in improved fuel economy and increased horsepower. The pump's design is similar to a mechanical fuel pump but is more advanced to meet the engine's high-pressure requirements.

The high-pressure fuel pump works in tandem with an in-tank pump. The in-tank pump sends low-pressure fuel to the high-pressure pump, which then forces the fuel into the pumping chamber. The camshaft rapidly pushes the plunger up and down, constricting the space and forcing the fuel out at high pressure.

A fuel pressure sensor in the system helps regulate the volume and pressure of the fuel entering the pump. This sensor, along with the powertrain control module (PCM), ensures that the engine receives the ideal fuel pressure in real time.

A properly functioning high-pressure fuel pump is essential for the engine to perform correctly. If the pump fails or malfunctions, it can lead to drivability issues and other problems. Therefore, regular maintenance and diagnostics are crucial to ensure the pump's performance and longevity.

Frequently asked questions