5 Common Symptoms of a Malfunctioning Fuel Pump

The fuel pump is an integral element of any car. Given the responsibility of literally pumping a vehicle’s fuel from its tank to the engine, a malfunctioning fuel pump will always lead to total disaster. Therefore, drivers need to be aware of the common symptoms of a malfunctioning fuel pump so as to address the problem before it leads to a car or truck that won’t start.

This guide is designed to explain the 5 most common signs of a failing fuel pump in an effort to educate drivers. That process begins with an explanation of the role and function of the fuel pump itself, which will help vehicle owners to understand the reasons behind fuel pump malfunction. Next, 5 common symptoms of a malfunctioning fuel pump, including everything from engine misfires to cars that won’t start, will be described. By the end of this guide, car and truck owners will understand what symptoms to look for in their own vehicles so that they can catch a fuel pump malfunction before it leads to total vehicle failure.

All About Fuel Pumps

The fuel pump is an essential component of any vehicle with an internal combustion engine, principally, cars and trucks. With the job of forcing fuel from the gas tank towards the engine, a malfunctioning fuel pump will create a situation where the engine either gets too much or too little fuel due to too much or too little pressure in the line traveling from the tank to the engine. This will lead to performance issues with the car or truck itself.

In the most basic sense, in order for an engine to run properly, fuel in the form of liquid gasoline needs to travel from the tank where it is stored to the engine where it is burned to create power and propel the vehicle. Some smaller, more concisely constructed vehicles, such as certain models of motorcycles, do not require a fuel pump because gravity takes care of this job. However, this is not the case for most internal combustion engine vehicles. Instead, they utilize either a mechanical or electronic fuel pump.

The Mechanical Fuel Pump

Traditionally, all fuel pumps were always mechanical. This means that they operate through a system that runs off of the rotation of the engine itself. A mechanical fuel pump resembles a diaphragm. It uses the pumping action of that diaphragm shape to create low pressure (10 to 15 psi) and transport fuel from the gas tank to the carburettor… This action resembled that of a piston.

Mechanical fuel pumps are located on a mount outside of the fuel tank itself and, in general, are less likely to malfunction than electronic fuel pumps. The most common malfunction of mechanical fuel pumps comes when the diaphragm inside the pump splits, disturbing the pressure balance of the pump. The other cause for mechanical fuel pump malfunction is high heat created from both the engine and the air outside turning the fuel to vapour. This prevents the pump from operating since it is designed to handle liquid only.

The Electronic Fuel Pump

Though the mechanical fuel pumping system was always sufficient for carburettor-based fuel systems, eventually vehicle manufacturers moved past the use of carburettors in favour of a more advanced fuel injection system… Though the fuel pump itself is still necessary, the mechanical pump cannot generate the level of pressure needed to work with fuel injection engines. Therefore, a new system which delivers fuel under high pressure (40 to 60 psi) was created. This system is what is known as an electronic fuel pump.

Nowadays, most vehicles use an electronic fuel pump, which is located within the gas tank itself, to deliver fuel to the engine. However, there are far more inherent issues with electronic fuel pumps. The electronic system works by spraying a fine mist of fuel inside the engine’s chambers and is operated through a computer control system rather than a mechanical one. As a result, both issues with the pump itself as well as the computer used to operate it can lead to vehicle and fuel pump malfunction.

After understanding the function of a fuel pump itself as well as the important differences between mechanical and electronic fuel pumps, understanding the common symptoms of problems with this component will make more sense. Remember, the purpose of a fuel pump is twofold:

  1. It pushes (or pumps) fuel from the gas tank to the fuel injector or carburettor.
  2. It creates the proper amount of pressure (low or high) to ensure that the right amount of fuel will be delivered to the engine, regardless of external conditions.

Therefore, malfunctions in the fuel pump can result from an issue in either one of these processes. Let’s take a look at the common signs of these problems.

1. The Engine Sputters at High Speed

The most common early sign of a problem with a fuel pump comes when driving a vehicle at a consistent high speed. While traveling down the road, the car will run well for about 10 miles and then begin to jerk around, or sputter, for a mile or two before returning to normal.

What This Means

Many people will mistakenly diagnose a sputtering vehicle as one with “dirty” gas or some other fuel-related issue. And while that can be the case, it is not uncommon for a fatigued fuel pump to create this same symptom as it struggles to supply a constant stream of fuel to the engine at the proper pressure. The loss of pressure causes the engine to sputter.

2. Vehicle Loses Power While Accelerating

The feelings generated by this second symptom are very similar to the first. However, rather than experience a sputtering sensation while driving, vehicles will experience it upon acceleration from a stop. Generally, the vehicle will initially move before making noises and jerking around as if it will stall. Then, it will continue on its acceleration path smoothly.

What This Means

The process of acceleration creates an increased demand for fuel by the engine. A malfunctioning fuel pump, again, cannot maintain the required pressure to deliver this fuel in a steady manner, thereby causing the engine to improperly mix fuel and air and lose power. Once pressure is restored, the engine is able to run smoothly and the car takes off.

3. Sudden Loss of Power When the Vehicle Is Under Stress

A car or truck is put under stress when the work needed to complete an ordinary task, such as forward movement, is somehow hindered by external forces. Generally, this occurs when climbing a hill or when hauling a load. If, when completing these tasks, the vehicle loses power, cannot accelerate, or begins to sputter, the fuel pump is a possible culprit.

What This Means

Generally, a fuel pump, even an aging one, can maintain a steady stream of fuel and pressure when operating under normal conditions. However, once put under stress, the weakening elements of the pump will begin to take control and the fuel delivery will not be able to keep up with its demands, leading to power loss.

4. Surging

The opposite effect of the above symptoms, surging, can also be a sign of a malfunctioning fuel pump. A car that surges will be moving along normally at a consistent speed. Then, with no driver intervention, will pick up and “surge” forward, as if the gas pedal had been depressed.

What This Means

This is something that many people will mistakenly blame on the fuel filter since it is not “like” any of the other fuel pump malfunction signs. However, this surge is created because, as a result of age and normal wear and tear, the fuel pump now has irregular resistance within its motor. This creates a situation where the pump cannot draw enough electricity to maintain the pressure needed for steady speeds and may “surge” with a sudden ratcheting up in pressure.

5. The Engine Will Not Start

The final symptom of a malfunctioning fuel pump is also the most severe. Drivers who ignore the signs listed above will all eventually end up here. When a car or truck’s engine will not start as a result of a fuel pump malfunction. Basically, the engine will rev, but it will not catch.

What This Means

When a fuel pump has malfunctioned to the point that the car will no longer start, this means that there is no fuel reaching the engine upon ignition. For that reason, drivers will hear the sparks try to ignite, but there will be no fuel to burn. To diagnose a fuel pump malfunction, check for a blown fuse and pressure in the fuel line (it will be 0).


As an essential element of any internal combustion engine system, the fuel pump is one of those automotive issues all drivers need to keep in mind. Like any aspect of vehicle operation, understanding what a fuel pump does and the different ways that it can fail can help drivers avoid bad situations with a failing car or truck. With the important tasks of delivering fuel to the engine as well as maintaining a consistent stream of pressure while doing so, a malfunctioning fuel pump will present in several ways.

The 5 most common symptoms of a malfunctioning fuel pump include sputtering at high speeds, loss of power during acceleration, loss of power to the vehicle while under stress, surging, and, finally, an engine that will not start. Understanding these symptoms and correctly identifying them early is the only way that drivers can avoid getting to the point where their vehicle will not start, stranding them and costing a lot of money in repairs.

Posted in Technical Articles