Fuel Pump Pressure: Low Volume, What's Wrong?

A fuel pump that can deliver adequate pressure but not enough volume may allow the engine to start and idle normally, but it will starve the engine of fuel and cause a loss of power when the engine is under load, accelerating hard, or cruising at high speeds. A pump that is on its last legs can cause the engine to be difficult to start, idle roughly, hesitate, lack power under load, or run lean. Low fuel pressure can cause hard starting, a rough idle, misfiring, hesitation, and stalling.

Clogged fuel filter

A clogged fuel filter can cause a range of issues with your vehicle's performance and, if left unaddressed, can lead to costly repairs.

Fuel filters screen debris and prevent contaminants from reaching the engine, but over time, they can become clogged due to trapped dirt and waste particles. This can cause a restriction in fuel flow and even a complete stoppage. As a result, your vehicle may experience a loss of power at highway speeds, lowered fuel economy, and hesitation during acceleration. Engine misfires, rough idling, and stalling are also common symptoms of a clogged fuel filter. In some cases, you may hear knocking or unusual noises coming from the engine, indicating that it is not receiving enough fuel.

If the clogged filter is not replaced, it can lead to more serious problems, such as clogged fuel injectors, a burnt-out fuel pump, or even CAT burnout from overheating. Therefore, it is essential to maintain and replace fuel filters regularly, typically between 30,000 to 50,000 miles or every 4 to 5 years, depending on the vehicle.

To avoid these issues, it is recommended to pay close attention to warning signs and maintain regular maintenance. A clogged fuel filter can often be identified by observing the performance of your vehicle and addressing issues in a timely manner.

Low voltage to the pump

Low voltage to the fuel pump can cause a range of issues, from a malfunctioning engine to a complete failure to start. Voltage to the pump is varied to control the speed of the pump, and therefore the fuel pressure. If the voltage is too low, the pump will not work normally, and there will be a drop in fuel pressure. This can lead to a range of issues, from hard starting, to stalling, hesitation, and misfiring.

Low voltage can be caused by a number of factors. A broken wire connection or weak battery can cause low voltage, and therefore a drop in pump pressure. It is also possible for there to be an issue with the power module, or a short in the fuel injection harness.

It is important to note that low voltage at the pump can also be caused by a problem elsewhere in the system. For example, a faulty relay, or a fault in the wiring circuit that provides power to the relay, can cause low voltage at the pump. It is also possible for there to be high resistance in the pump's ground connection, which can prevent the pump from running or spinning fast enough to generate adequate fuel pressure.

To diagnose low voltage at the pump, it is important to check for voltage at the pump, and to ensure that the pump is receiving the correct voltage. If the voltage is low, the wiring connectors, relay, and ground should be checked. It is also important to check the fuel filter and lines for obstructions, as these can also cause low pressure.

Cracked or clogged fuel lines

A vehicle's fuel injection line is a network of flexible and rigid lines used to transport fuel throughout the fuel system. Fuel lines can become cracked or clogged, leading to issues with engine performance and safety hazards.

Symptoms of a Cracked or Clogged Fuel Line

• Poor gas mileage: A fuel leak can cause a noticeable decrease in fuel efficiency.
• Fuel smell: Leaked fuel will fill the air around the vehicle with the smell of gasoline.
• Visible fuel leaks: Fuel dripping on the ground or puddles under the vehicle indicate a severe fuel leak.
• Engine issues: A blocked or leaking fuel line can cause engine sputtering, cutting out, hard starting, rough idle, misfiring, hesitation, and stalling.
• Safety hazards: Fuel spraying or leaking from a faulty fuel line can come into contact with a heat source and ignite, leading to smoke in the engine compartment and potential fire hazards.

Causes of Fuel Line Issues

• Fuel breakdown: Over time, fuel can soak into the hose and break down the material, causing cracks and leaks.
• Ethanol in modern fuel: Some hoses are more prone to breakdown due to the ethanol content in modern fuel.
• Corrosion: Metal parts of fuel lines can suffer from corrosion.
• Age and abrasion: Fuel lines will eventually break down due to age, and debris can cause abrasion.

Diagnosis and Repair

To diagnose a cracked or clogged fuel line, carefully inspect the fuel lines for visible signs of damage, such as cracks, leaks, or damp areas with a buildup of gunk. If you suspect a fuel line issue, it is recommended to tow your vehicle to a mechanic for further diagnosis and repair.

Faulty fuel pressure regulator

A faulty fuel pressure regulator can cause a host of issues with your vehicle's performance and fuel efficiency. The fuel pressure regulator is responsible for ensuring the correct amount of fuel is supplied to the engine by regulating the pressure of the fuel. When this component malfunctions, it can lead to the following issues:

• Engine performance problems: A faulty regulator can cause a loss of fuel pressure, leading to hard-starting, rough running, stalling, and a lack of power.
• Check engine light: The car's engine computer will often recognise issues caused by a faulty regulator and turn on the check engine light. It will also store a corresponding diagnostic trouble code (DTC) in its memory.
• Black smoke from the tailpipe: A faulty regulator can cause the engine to run rich, resulting in black smoke emitting from the exhaust.
• Fuel in the regulator's vacuum line: A ruptured diaphragm within the regulator can cause fuel to leak into the vacuum line.
• Vehicle cranks but doesn't start: A faulty regulator can prevent the engine from receiving the proper fuel pressure, resulting in a vehicle that cranks but fails to start.
• Engine misfires: Interruption in the vehicle's fuel pressure can cause the engine air-fuel ratio to be thrown off, leading to engine misfires.
• Decrease in power, fuel efficiency, and acceleration: A faulty regulator can affect the vehicle's performance, resulting in reduced power, poor acceleration, and decreased fuel efficiency.
• Fuel leaks: Failure of the regulator's diaphragm or seals can lead to fuel leaks, which pose a safety hazard and can also impact engine performance.
• Irritating noise from the fuel pump: When the fuel regulator malfunctions, the normally humming fuel pump can start making an irritating noise, especially in traffic jams.

It is important to note that these symptoms may also be caused by other mechanical issues, so proper diagnosis by a professional is always recommended.

Defective fuel pump relay

A fuel pump relay is an electromagnetic switch that controls the current passing to the fuel pump. It is typically controlled by the ignition and ensures a power supply to the fuel pump. If the relay is defective, it cuts off the power to the pump, causing the engine to stall.

• The engine cranks but does not start: This is the most common sign of a bad fuel pump relay. The relay will usually fail in the open position, preventing voltage from reaching the fuel pump. As a result, the engine will not receive enough fuel and refuse to run.
• The fuel pump runs continuously: In some rare cases, the fuel pump relay can get stuck in the closed position, causing the fuel pump to run non-stop. This issue mainly occurs in circuits that supply constant power to the fuel pump fuse.
• The check engine light illuminates: In some vehicles, the engine computer or the powertrain control module (PCM) monitors the fuel pump relay and its circuit. If the PCM detects an issue, it turns on the check engine light and stores a corresponding diagnostic trouble code (DTC) in its memory.
• Multiple attempts to start: The vehicle may require multiple attempts to start, especially when the engine is cold. This problem tends to worsen over time, eventually leading to a complete failure to start.
• Unexplained battery drainage: A fuel pump relay that is stuck in the closed/on position can cause the fuel pump to run continuously, draining the battery. This issue may persist even after installing a new battery or fuel pump.
• The vehicle starts in warm months but not during colder months: A faulty fuel pump relay may cause issues with starting the vehicle during colder months.
• The engine stalls after starting or while driving: The vehicle may start but stall after a few seconds or minutes. This could be due to the fuel pump relay failing to supply power to the fuel pump, resulting in the engine stalling.

If you suspect a defective fuel pump relay, it is recommended to consult a professional mechanic for an accurate diagnosis and appropriate solutions.

Frequently asked questions