5 Common Symptoms of a Malfunctioning Fuel Pump

The fuel pump is an integral element of any car or truck. Given the responsibility of literally pumping a vehicle’s fuel from its tank to the engine, a malfunctioning fuel pump will usually lead to total disaster. Car owners should be aware of common symptoms of a malfunctioning pump so they can take a preventative measure before the worst happens.

This guide is designed to explain the five most common signs of a failing fuel pump. That process begins with an explanation of the role and function of the fuel pump, which will help vehicle owners to understand the reasons behind a malfunction. Next, we’ll detail common symptoms, everything from engine misfires to cars that won’t start. By the end of this guide, car and truck owners will understand what symptoms to look for in their own vehicles.

All About Fuel Pumps

The fuel pump is an essential component of any vehicle with an internal combustion engine, principally, cars, SUVs, and trucks or even a hybrid diesel. A malfunctioning fuel pump delivers too much or too little fuel from the gas tank. While you’re scratching your head looking at a full fuel gauge, an engine starved of gas will leave you stranded in the garage or on the side of the road. Motorcycles and some other vehicles don’t require a fuel pump, relying on gravity to feed gas to the engine. Other internal combustion engines use either a mechanical or electric fuel pump.

The Mechanical Fuel Pump

The granddad of the industry is the mechanical pump. A mechanical fuel pump most always resembles a diaphragm. It uses the pumping action of that diaphragm shape to create low pressure of between 10 and 15 per square inch (psi) and transport fuel from the gas tank to the carburetor. This action resembles 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 occurs when the diaphragm inside the pump splits, disturbing the pressure balance and sending the fuel into a carburetor float bowl. The other cause for mechanical fuel pump malfunction is high heat created from both the engine and the air outside turning the fuel to vapor. This prevents the pump from operating, because it is designed to handle liquid only.

The Electronic Fuel Pump

Although the mechanical fuel pumping system was always sufficient for carburetor-based fuel systems, eventually vehicle manufacturers moved past the use of carburetors in favor of a more advanced fuel injection system. Although 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 that delivers gas or diesel under high pressure, such as between 40 and 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 gas or diesel. 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 malfunction and breakdown.

Remember, the purpose of a fuel pump is twofold:

  1. It pushes or pumps fuel from the gas tank to the fuel injector or carburetor.
  2. It creates the proper amount of pressure 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 comes when driving a vehicle at a consistently high speed. While traveling down the road, the car will run well for about 10 miles and then begin to jerk or sputter before returning to normal.

What This Means

Many members of the driving community at times will mistakenly diagnose a sputtering vehicle as one with “dirty” gas, an almost empty tank or some other fuel-related issue. 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

With a similar symptom to the previous, vehicles will jerk during acceleration from a stop. The car may produce a stalling sound and then accelerate smoothly.

What This Means

Once you take your foot off the brake and hit the gas pedal, a working pump increases the flow of gas or diesel to fuel acceleration. Because a malfunction starves your car of that increased flow, it doesn’t have the power it needs to respond to commands. 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, even an aging pump can maintain a steady stream of fuel and pressure when operating under normal conditions. These devices create resistance or fail when under stress, leading to power loss.

4. Surging

If your vehicle doesn’t lose power while driving, you may find it surges – accelerating suddenly with no drive input.

What This Means

Some may mistakenly blame this on the fuel filter, reasoning that it is not properly trapping dirt and rust. More likely, this surge is created because, as a result of age and normal wear and tear, the fuel pump 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 pump is also the most severe. Drivers who ignore the signs eventually will end up here, with a car or truck that won’t start.

What This Means

When a 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 such a malfunction, check for a blown fuse and pressure in the fuel line, as the gauge should read 0.


An essential element of any internal combustion system, understanding what a fuel pump does and the different ways that it can fail can help drivers avoid bad situations with a car or truck.

The five 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 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 them a lot of money in repairs. Replacing a faulty fuel pump is not as simple as an oil change. People interested in changing a fuel pump without a mechanic should exercise caution, working in an environment where the temperature will not ignite gas fumes and using a premium pump assembly. They should work on an empty gas tank, and become familiar with a car’s valves and electrical connectors. A car owner can gain detailed instructions on how to make a fix through online forums.

Leave a Reply

Your email address will not be published. Required fields are marked *