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Electric Fuel Pump – Basics of Operation, Symptoms, and Repair

eEuroparts.com Fuel Pump Electric Fuel Pump - Basics of Operation, Symptoms, and Repair

Modern engines are slowly moving towards reaching optimal efficiency. We’re seeing new designs and technologies hit the market every year, ensuring better performance and fuel consumption. However, most of that performance relies on the electric fuel pump doing its job.

Without a properly working fuel pump, your car is left dead in the water. Today we’ll go deep into fuel pumps, how they work, why they fail, and how to figure out if yours is about to go.

Anatomy of an Electric Fuel Pump

The Heart of an Engine

Despite how far we’ve got from the early automotive design, some things haven’t changed much. One of them is the use of gas tanks in the rear of the vehicle. Getting the gas from the tank to the engine is a seemingly simple task. All you need to do is create enough pressure in the system to send the gas up the lines and into the fuel rail.

To get this done reliably, you need a dedicated fuel pump. There are several types of fuel pumps out there, but the in-tank electric pump still reigns supreme.

Anatomy of an Electric Fuel Pump

Your average fuel pump is extremely simple. It’s essentially a small electric motor that’s encased in a sealed shell. As the motor spins, it’s sucking in fuel and sending it further down the line at a certain pressure. The pressure itself is extremely important for the operation of modern gasoline engines. Most motors use high-pressure fuel injectors, which demand highly pressurized fuel delivery.

That being said, the fuel pump is a part of a slightly larger system – the fuel pump assembly. An average fuel pump assembly includes the pump, the fuel sender unit, a fuel pressure sensor, and some kind of filter that’s attached to the pump itself.

The entire assembly is submerged inside the fuel tank, often reaching its lowest point. That way, the pump gets to suck in all of the gasoline from the tank.

In-Tank Fuel Pump Failure – Common Reasons

Having a broken electric fuel pump is proof that even the simplest devices in a car can fail. That being said, fuel pumps rarely ever fail out of the blue. There’s usually a very good reason why a fuel pump is dead. Let’s go over some of the most common causes of fuel pump failure.

Driving on Empty

Efficiency is everything in engineering. When the fuel pump design stepped away from the mechanical standalone type to an in-tank electric type, the engineers managed to solve two issues in one go. For one, they’ve made the whole system much more efficient and capable of feeding modern fuel injected engines. In addition to that, they’ve managed to solve the pump overheating issue.

The electric motor that runs the pump gets hot. All that heat that’s produced inside a fuel pump is the byproduct of prolonged gasoline delivery at extremely high pressures. Here’s the thing, though – submerging the fuel pump inside the tank has not only made it more efficient, but it provided engineers with a simple way to cool the pump down. The gasoline acts as a coolant.

As you’ve probably figured out by now, when the gas levels drop way below the minimum, the pump will start to overheat. Driving on empty for prolonged periods of time is the number 1 reason for fuel pump failure in modern vehicles.

Once the gas levels around the pump drop below a certain level, it will start overheating, and that’s when the troubles start.

Fuel Contamination and Debris

Another big reason why an electric gasoline pump fails is sucking debris into the system. Almost every pump has a built-in strainer at the bottom that serves to filter out any debris. However, these strainers aren’t 100% effective, resulting in all kinds of stuff finding its way into the pump mechanism.

The debris we’re talking about includes dirt, particles of rust, or anything else that could have found its way into the tank.

fuel pump Symptoms of a Failing Fuel Pump

Water Ingress

Water and electronics rarely every mix well. Water delicate fuel pumps full of metal components that have to remain oxidation-free never mix well together. At this point, you’re probably wondering how does water even get inside a fuel tank?

We can attribute water ingress to bad fuel cap seals, bad fuel, or any number of other reasons, including condensation. When exposed to enough water or moisture, the fuel pumps will rust. Once that happens, you’ll often see the stator and rotor starting to stick together or gears slowly grinding down to where they’re not performing their function anymore.

Symptoms of a Failing Fuel Pump

When a fuel pump goes bad, it can cause a whole slew of issues that could set you off on a wild goose chase. Some of the symptoms are very ubiquitous, while others are easier to figure out. Let’s start from the easiest to diagnose and work our way from there.

Failure to Start

What usually happens with fuel pumps is the following – you get in your car heading to work, put your seatbelt on, key in the ignition, give it a crank, and it refuses to start. One somewhat good thing about fuel pumps is that they’re almost always binary when it comes to function. In other words, they either work, or they don’t.

Diagnosing the issue in a failure-to-start situation can be done in two ways. The easiest one is to listen to the pump.

When you turn the key into the accessory mode, the power is sent to the pump. It’s spun for a few seconds, giving you that initial gasoline pressure to start the engine. If you listen close enough, you will hear a humming noise that lasts for a few seconds coming from the rear.

It could be difficult to hear on some newer cars, but opening the fuel cap and putting your ear close to it while someone turns the ignition solves that problem.

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Bad Relay

Fuel pumps, much like other important systems in a car, are controlled by relays. A dead relay could easily cause a failure to start problem as the pump is no longer receiving power from the battery. Unfortunately, the only way to determine this is to find the relay and either listen to see if it’s engaging or testing on a test bench.

Fuel Pressure Issues

If you’re among those few percent that fall between the binary either working or not working nature of fuel pumps, you’ll most likely deal with fuel pressure issues.

These can materialize in a whole variety of forms.

Intermittent Power

When the fuel pump is no longer capable of delivering the necessary pressure, one of the main symptoms is intermittent power. The engine will have dips in output, causing the car to either lose power during acceleration completely or intermittently.

We can generally trace the issue back to the rotor portion of the fuel pump sticking to the stator, causing the pump to work with constant interruptions. Diagnosing this issue is a matter of eliminating potential causes. There’s no reliable way to pinpoint the problem without taking the pump out of the tank and testing it manually.

Fuel Pump Replacement

Okay, now that we understand how fuel pumps work, why they fail, and how they behave when they fail, let’s talk about fixing the problem. Fuel pump replacement can be a simple job or a difficult job, depending on your car’s design.

We’ll mainly talk about in-tank submerged fuel pumps in this part of the guide. We’ll touch upon mechanical pumps and inline pumps some other time.

When looking for a replacement pump, you might find that your car can use a universal pump. Universal pumps make things easier in terms of sourcing parts. You can use our navigation tool to find out which pumps fit your car’s make and model.

There are two ways you can access a submerged fuel pump that’s sitting inside the gas tank – through the trunk/back seat area or by dropping the entire tank. Some cars have an access port inside the passenger cabin, some don’t. Check your user manual or consult a master technician to determine what you’re dealing with in your particular case.

Either way, the replacement process is the same. The fact that you might have to drop the tank only complicates the part of the process related to reaching the pump in the first place.

Remember to disconnect the battery before proceeding further.

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Step 1 – Access the Pump

Again, either track down the access port usually found behind or under the back seat or drop the entire tank. Once you locate the access port, you’ll find a large plastic ring that seals the fuel pump assembly.

Step 2 – Disconnect the Fuel Lines and Electrical Connections

This step is pretty straight forward. You’ll find all the gas lines and connectors at the top of the fuel pump assembly.

Step 3 – Remove the Plastic Ring and Rubber Seal

Once you’ve located the pump, remove the plastic ring and the rubber gasket seal underneath.

Step 4 – Remove the Fuel Pump Assembly from the Tank

Once you pull the fuel pump assembly out, you have two options – either replace the whole thing or replace the pump only. To replace the fuel pump, simply unhook it from the internal connectors and gas lines, and pull it out. Take your new pump and reverse the process.

Step 5 – Reassemble Everything

Once the new pump or fuel pump assembly has been installed, simply reverse the process and put everything back the way it came off. When everything is assembled again, connect the battery and turn the key to accessory mode 2 or 3 times before cranking the engine. That way, your new pump will have enough time to generate pressure in the system.

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Where to Get Quality Electric Fuel Pumps?

Here at eEuroparts.com, we offer a wide range of quality electric fuel pumps made by top tier manufacturers. You’ll find pumps for most European vehicles produced by brands such as BMW, Audi, VW, Mercedes, Volvo, Porsche, and others.

If you have any questions regarding our selection of electric fuel pumps, feel free to contact our customer support service via email. Our reps are standing by to offer any assistance you might need.

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3 thoughts on “Electric Fuel Pump – Basics of Operation, Symptoms, and Repair

  1. Why don’t you just tell us what the item you are offering costs ? Say, “$149 -$540 depending on the quality ” ?

    1. Our fuel pump units span from around $50 for just the pump motor, up to about $600 for Genuine OEM replacement parts. Thanks for shopping, hope this article helped you get a better understanding of the situation inside your fuel tank!

  2. I will definitely consider you next time. I have bought Bosch Fuel Pump last month for my car. They are working good.

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