Fuel pumps have one of the highest rates of return at FCP Euro, and it’s easy to see why. Fuel systems can be pretty complex, with many electrical and mechanical parts influencing fuel delivery to the engine. Common causes include a debris-filled fuel filter, blocked fuel line, blown fuel pump fuse, bad fuel pump relay, and electrical faults in the fuel wiring pump wiring. Because of that, many pumps find their way back to our distribution centers unused, as the problem wasn’t ever the pump itself. Instead of buying a pump, waiting for it to arrive, and replacing it only for nothing to change, read the following guide to learn how to diagnose your fuel delivery issue before throwing money at parts.
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How Does An Electric Fuel Pump Work?
The fuel system includes everything within the vehicle that stores, transports, and monitors the fuel. The fuel pump is the device that provides that transportation, sucking up the fuel, pressurizing it, and sending it through hard and soft fuel lines to the fuel injectors on the engine. In almost every car, the pump will sit inside the fuel tank as a part of the fuel-level sending unit and come with an attached filter.
Your chances are pretty good that when the ignition is engaged, the fuel pump will run or run briefly to prime the fuel system. Try to recognize the sound moving forward, as that can indicate its health. If the fuel pump does not function with the ignition on or while the engine is cranking, the problem may be the pump. Fuel pump failures aren’t chronic issues for any one model or brand (barring high-pressure fuel pumps), but they do happen on older vehicles or those with higher mileage. After 100,000 miles or so, your chances of a failure are significantly higher, so consider some preventative maintenance.
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However, many modern engines use a second fuel pump for their direct fuel injection systems. That pump is a high-pressure fuel pump, which isn’t covered in this article. High-pressure pumps are mechanically driven and operate entirely differently from an electric pump. Stay tuned to the blog for our eventual article covering all the symptoms and diagnosis processes for high-pressure fuel pumps.
Five Signs You May Have A Bad Fuel Pump
The Engine Dies Immediately After Starting
There is almost always residual fuel and pressure within the fuel system after the engine stops, and it’s occasionally enough to briefly start the engine. However, if the pump is dead, the engine will soon die and refuse to restart. A dying pump that lacks the proper pressure to provide enough fuel while running may be able to build enough for a brief start if allowed to run with the engine off. But an utterly dead pump won't be able to prime the fuel system with gasoline or pressure, so if it doesn’t restart, it’s likely the pump.
Your Car Hesitates Under Acceleration
The engine should respond smoothly as you roll away from a stop sign or light and feed in throttle. Anything that may feel like the engine briefly cuts out, bogs, or hesitates indicates an issue somewhere. If your fuel pump is in the early stages of failure, it may struggle to provide the proper pressure for acceleration. It could be a problem with the ignition system, but misfires are reasonably quick to cause engine warning lights, so if nothing appears, it’s likely an issue elsewhere.
Your Engine Dies While Driving
There are many reasons why an engine may stop while running; that’s just the unfortunate truth. However, plenty of context clues can help you determine the cause. A long crank or hesitancy to start are some of the best clues you can have, but electrical issues can also cause them. The real determining factor will be how the car sounds and looks when you turn the key. If the engine struggles to turn over and the interior light and gauges go dim, it’s likely an electrical issue causing the slow start. When fuel-related, the starter shouldn’t have any problem turning the engine, but the engine will still struggle to start. If the pump is weak enough to struggle upon start-up, it probably won’t make it very far, and it’ll be while you’re driving.
The Fuel Pump Makes Uncharacteristic Noises
Throughout history, there have been many kinds of fuel pumps that have made all sorts of noises. Some make a constant clicking noise, others a rhythmic knocking, but all modern pumps will hum. It won't be deafening, and you won’t hear it while the engine runs, but when you turn the key to the on position, you should be able to listen to it run. If a failing or failed pump is damaged mechanically, its specific tone will change. Personally speaking, a recent pump failure of my own was partially determined by it sounding like it was attempting to eat gravel, as the plastic gears within had broken.
Your Car Simply Won't Start
A car that won’t start is either the worst or best-case scenario, depending on where you are. If it's in your driveway and you have another way of getting to work, then it's not that big of a deal. If it's a hundred miles away from home in the middle of a storm, you’ve much more to worry about. Hopefully, the latter doesn't happen to you.
A dead pump is a dead pump; there’s no way around it. More often than not, they’ll finally give up the ghost while not using it, whether sitting for a while or freshly after a drive. If all of your electrics work, it’s not likely to be the ignition system or anything to do with the electricity supply. As mentioned earlier, immobilizer units can be the cause, but rarely and typically only on specific models.
How to Check Your Fuel Pump’s Condition
Remove a Fuel Supply Line
Diagnosis doesn’t have to be complicated, especially not with a fuel pump. When the key enters the ignition position in most vehicles, it energizes the fuel pump, priming the fuel system by sending pressurized fuel to the injectors to prep them to supply the engine. If not, you may be able to jump a relay and activate the pump. Use that to your advantage by disconnecting one of the rubber fuel supply lines in the engine bay and watching for pressurized fuel.
Disconnect the line BEFORE priming the fuel system and place the end of the line in a clear plastic bottle so that it sprays into a container. If fuel comes out of the line pressurized like it should, then the problem is likely elsewhere. However, it’s not a guarantee, as the pressure it comes out with is also determined by pump health.
Use a Multimeter and a Wiring Diagram
Fuel pumps don’t hang out in the open, but they’re not the worst to get to. In most cases, you’ll have to remove a back seat or trunk panel to reach an access cover in the chassis that opens up to the fuel pump. There, you’ll find the cover to the fuel level sender assembly, which carries the pump, and the wiring connection that runs through it.
You can use a multimeter to probe the wiring at the connection to see whether or not the fuel pump is receiving electric power and the proper signal if it needs one. There’ll be more than a few wires at that connection, so find a wiring diagram online for your vehicle and determine which wires you’ll need to probe. If the pump has power, a good ground, and the proper signal at the connection, then the pump is likely bad. If not, there’s an issue elsewhere.
Disconnect The Fuel Pressure Sensor
As cars have advanced in the last few decades, the fuel pressure regulator has disappeared. In its place are variable fuel pumps that can adjust their pressure or are controlled by a separate fuel pump controller. The trick with these comes from disconnecting the fuel pressure sensor. Without the pressure sensor, you’ll likely get a check engine light, but the ECU will assume a worst-case scenario and order the fuel pump to run at full pressure. If your car runs better without the sensor, you’ve found your problem.
Test With a Fuel Pressure Gauge
In cases where the pump runs, and you’re sure fuel is reaching the injectors, you should check fuel pressure. You can use a flow meter to check the fuel delivery, or the pump's output can be measured by disconnecting a fuel line and seeing how much fuel it can deliver. A good pump would typically deliver a quart of fuel in 30 seconds, and most shop-grade fuel pressure regulators offer fuel lines to flow fuel with the pump engaged. Fuel pumps must be submerged in fuel for both cooling and lubrication. Running a pump dry will almost certainly damage it.
Frequently Asked Fuel Pump Questions
What About The High-Pressure Fuel Pump?
Great question! Nearly every major manufacturer has adopted direct fuel injection in the last two decades. The highly precise fuel delivery improves efficiency and boosts power compared to traditional port injection, but it also requires some extra parts, mainly the high-pressure fuel pump.
In the direct injection system, the high-pressure pump is fed by a standard in-tank pump before it pressurizes that fuel to well over 1000psi to be injected into the combustion chamber. They're driven mechanically via a lobe on a camshaft or off of a vacuum pump. High-pressure pumps can fail regularly and have presented issues for VW and BMW owners with notoriety. However, they’re typically monitored much more closely due to the sensitive nature of direct injection, so any problems will likely be captured by a check engine light or other warning message on the dashboard.
How Long Do Fuel Pumps Last?
Fuel pumps last a minimum of 80,000 miles. However, you don't typically need to replace your fuel pump until well beyond that, with some owners claiming the 200,000-mile mark without any issue. We recommend checking your pump over 120,000 miles if it is still original.
How Much Does It Cost to Replace a Fuel Pump / Fuel Pump Cost?
The cost of replacing the fuel pump depends on the make and model of the vehicle. Fuel pumps are simple and standard parts, so they won’t be the most expensive. Figure somewhere between $100 to $300 in parts cost, plus whatever else you may need for the job, like a new filter or sending unit. At a minimum, add 20% to the parts cost if you go to a dealership or independent shop for a professional repair. Then, tack on roughly two to three hours of labor at a minimum of $150 per hour.
Which Fuel Pump Should I Buy?
Genuine parts generally hold the best value when it comes to resale opportunities. If that doesn’t matter to you, get whichever fits your budget. All of the fuel pumps that FCP Euro carries are supplied by trusted brands that are OE in some way or another for an extensive range of European vehicles. Bosch is likely the most significant name you’ll see from a pump supplier, but VDO, Delphi, and Pierburg are just as popular for many models. Even Continental offers replacement fuel pumps for a select group, so shop confidently and take comfort knowing you’re protected by one of the best deals in the industry.
Is Replacing a Fuel Pump Difficult?
The answer to this question entirely depends on the make, model, type of pump, and previous history. Not all fuel tanks and pumps are located equally, but they should be relatively easy to access. It’s removing the fuel-sending unit to reach the pump, which can cause significant hang-ups.
Many European models use a large plastic or metal locking ring to secure the fuel-level sending unit to the top of the tank. Unfortunately, these can be a nightmare to remove due to a few factors, including debris build-up, rust, and age. Some models have a special socket to remove the ring, but not everyone is so lucky. If it’s not an in-tank pump, it’ll likely be upstream under the car. It shouldn't be a hassle if you can get under the vehicle. Once you reach the pump, no matter where it is, removal and replacement should be straightforward.
Can I Drive With a Bad Fuel Pump?
This is up to you. Depending on your symptoms, you technically can drive with a bad fuel pump; it all depends on how much of a risk you want to take. You might experience stalling in the middle of traffic, or your car might not start at an inopportune time. FCP Euro recommends replacing it when you begin experiencing symptoms.
With that, you should be all set on your fuel-pump-related journey. Hopefully, you can save yourself some time and lots of hassle with this short guide. As always, keep your eyes on the blog for more great content, and don’t forget about our two YouTube channels, where you can find DIY videos and fun build content.
