The fuel pump’s sole task is to export gas from the gas tank to the engine, and it carries out this task with other auto parts. That makes it tricky to know whether it’s failing or not unless you know bad fuel pump symptoms.
The essential key in diagnosing a vehicle is paying attention to how it normally works, acts, and runs on a daily basis. Does it usually make a sound? If yes, what sound does it make? What’s the vehicle’s normal RPM?
With this article’s help and attention to detail, you will be able to tell fuel pump problems and know how to fix them.
Knowing if your vehicle does hard starting, flexes less power, or struggles to idle fine is the first step to knowing if there’s a problem and preparing to fix it.
Because many vehicle components are interdependent and interconnected, a diagnosis could be a hard task at times. It involves trial and error, and finding the exact cause of a problem often requires professional assistance and an attentive mindset.
What is a fuel pump and how does it work?
A fuel pump is a small electric motor that transfers fuel from the tank to the engine. In older vehicles, the fuel pump is mounted along the frame rail, fastened into the fuel line.
Classic cars often use a mechanical fuel pump at the engine that pulls fuel to the front of the car rather than a pump at the back, pushing it forward.
Modern cars almost all have the fuel pump inside the fuel tank. The small cylindrical pump is part of a larger assembly that includes a fuel level sensor and a fuel filter screen.
Generally, pumps can produce more pressure by pushing fluid through the line rather than drawing it up.
A fuel pump for today’s engines usually uses an impeller-style system that pulls fuel through it, creating positive pressure on the engine side of the pump.
Other styles including a rotary vane and gearmotor pump are available for select models, but they’re far less common.
Once the pump has built pressure, it’s intended to hold it by preventing fuel from bleeding back into the tank. In this way, there’s always fuel in the line, primed, so you can start your engine quickly whenever you need to.
Most Common Symptoms of Bad Fuel Pump
The most common symptoms of a bad fuel pump include a stalling engine, excessive whining noises, engine sputtering, and noticeable drops in performance.
You might also experience surging, misfiring, the Check Engine Light turning on, worn spark plug tips, and low fuel pressure. When the fuel pump fails completely, the car won’t start at all.
Here’s a closer look at the most common bad fuel pump symptoms explained in detail.
#1. Engine Sputters at High Speeds.
If your car starts to hesitate or jerk while you’re driving at highway speeds, it could point to a weak fuel pump. It usually happens when the engine needs more fuel than the pump can deliver.
Instead of a smooth ride, it feels like your car is choking for a second or two. Drivers often brush it off the first time, but if it keeps happening, it’s worth getting checked out. This is one of the more common fuel pump symptoms.
#2. Loss of Power When Accelerating.
Pressing the gas pedal should give you a steady boost, not a sluggish crawl. If your car struggles to pick up speed, especially when merging or passing, it might not be getting enough fuel.
A failing fuel pump can’t keep up when the engine demands more power. You’ll feel like the car just isn’t responding the way it used to. That kind of lag is easy to notice and often shows up before other fuel pump symptoms.
#3. Trouble Starting the Engine.
If your engine cranks for longer than usual or takes a few tries to start, the fuel pump might not be delivering the pressure your engine needs. You might hear the starter turning, but the engine doesn’t fire up right away.
Over time, this can get worse until the car won’t start at all. It’s an early warning sign that often gets blamed on the battery or starter, but weak fuel delivery is a common reason behind hard starts.
#4. Frequent Stalling While Driving.
If your car randomly stalls while you’re driving, especially at lower speeds or when idling, a bad fuel pump could be the reason. It might start up again just fine, then shut off a few minutes later.
That kind of on-again, off-again behavior usually means fuel isn’t consistently reaching the engine. It can feel like the car just gives up for a second. Stalling like this isn’t just frustrating. It can become dangerous if it happens in traffic.
#5. Unusual Whining Noise from the Fuel Tank.
A low, constant whining sound coming from the area near your gas tank isn’t normal. A healthy fuel pump makes a quiet hum, but when it starts to wear out, it can get louder. That high-pitched whine often means the pump is struggling or running dry.
You’ll usually hear it when the engine is running and the car is at a stop. If that sound wasn’t there before and now it is, it’s worth having it checked out.
#6. Poor Fuel Efficiency You Can’t Explain.
If you’re filling up more often but your driving habits haven’t changed, your fuel pump might not be working right. A failing pump can throw off the fuel pressure, causing the engine to use more gas than it needs.
You might not notice it right away, but over time it adds up. If your mileage suddenly drops without a clear reason, it’s one of the fuel pump symptoms that can quietly cost you more at the pump.
Fuel system cleaning may help in some cases, but if the pump is worn, it needs to be inspected.
#7. Sudden Surges in Speed.
If your car unexpectedly speeds up without you pressing harder on the gas, that’s not normal. A failing fuel pump can send uneven amounts of fuel to the engine, causing random surges.
One second you’re cruising steady, the next your car jumps forward. It feels unpredictable, especially during stop-and-go traffic or while slowing down.
These surges aren’t just strange. They can affect your control behind the wheel and create risky situations if they happen around other vehicles.
#8. Difficulty Climbing Hills or Towing.
When your vehicle struggles on hills or feels underpowered while towing, it could be more than just extra weight. A weak fuel pump may not supply enough fuel when your engine is under stress.
You might notice the engine bogging down or the vehicle slowing even when you’re pressing the pedal harder.
That lack of power becomes most obvious when your car needs a little extra push. If these situations feel harder than they used to, the fuel pump might be to blame.
#9. Engine Misfires Under Load.
If your engine starts to misfire when you’re accelerating, towing, or driving uphill, a failing fuel pump could be behind it. Misfires happen when the engine isn’t getting the right mix of air and fuel.
Under load, the demand for fuel increases, and a weak pump might not keep up. You might feel jerking or hesitation, almost like the engine is skipping a beat. Fuel pump symptoms like these usually show up when your car is working the hardest.
#10. Car Won’t Start at All.
If your engine cranks but never starts, the fuel pump may have stopped working completely. At this point, no fuel is reaching the engine, so it has nothing to ignite. You might still hear the starter clicking or turning, but the engine won’t catch.
This usually happens after other warning signs were missed or ignored. If the pump fails, you’re stuck. When your car suddenly won’t start and there’s no clear reason, fuel delivery should be one of the first things checked.
#11. Check Engine Light Comes On.
When the check engine light shows up, it can mean a lot of different things. One of them is a fuel pump that isn’t keeping a steady pressure. Your car’s sensors notice when fuel delivery is off, and that’s often enough to trigger the warning.
You might not feel a difference in how it drives right away, but the light means something isn’t right. If that light appears along with other fuel pump symptoms, it’s time to get it looked at.
#12. Overheating Fuel Pump After Long Drives.
If your car starts fine but has trouble after longer drives, the fuel pump could be overheating. A worn pump can get too hot the longer it runs, especially if it’s working harder than it should.
After driving for a while, you might notice stalling, rough idling, or the engine shutting off completely. Letting the car cool down might help it start again, but the issue keeps coming back. Heat-related failure is a clear sign that the fuel pump is wearing out.
What causes a fuel pump to go bad?
Overheating by consistently driving with very low fuel.
You know how you like to tempt fate by driving around with your fuel gauge reading empty?
That’s exactly the type of behavior that will kill your fuel pump prematurely. The reason being is that the pump has to work harder to pull fuel from the tank when the level is low.
Eventually, the overworked pump will overheat, leading to its early demise.
#1. Restricted fuel filter.
Some cars have an external fuel filter. If your fuel filter becomes clogged or needs to be replaced, the pump will have a harder time pushing fuel through.
#2. Dirt and debris.
Even though the pump has a strainer, smaller particles can make their way through, causing damage.
So, if you’ve replaced your fuel pump recently, and you didn’t clean the tank before installing the replacement, the dirt and debris that have accumulated at the bottom of your gas tank can actually cause damage to the new fuel pump.
#3. Water contamination.
Water contamination can also lead to rust and corrosion that damages the fuel pump. Often, the moisture accumulates after the vehicle has been sitting unused for an extended period of time.
#4. Normal wear and tear.
Of course, fuel pumps don’t always fail due to outside forces, such as running the fuel tank low and contamination. It’s also very common for a fuel pump to simply wear out over time.
How to diagnose and replace a bad or faulty fuel pump?
Before you swap out the fuel pump, there are a few things you want to check once you notice any of the symptoms mentioned above. I will show you how to check it just in case it isn’t the fuel pump that is faulty and it is something much easier to deal with.
So the first thing you want to do is grab the key, put it in the ignition and you want to turn it to the ON position. Listen closely to see if you hear any sort of hum or whining sound from the back of the car.
Now you didn’t hear anything; does this mean fuel pump is bad? Not necessarily, it could have something to do with a bad relay, blown fuse, etc. that you will need to replace.
Grab your owner’s booklet and start flipping through the book until you find the page that deals with fuses and where to find the fuel pump fuse.
You want to take out the fuse and visually inspect the fuse. Also, you want to take your multimeter and test the voltage on the fuse holder as well. Typically the voltage should be around 12:00.
You may also want to verify the fuel pump is getting power. You can do this by locating the fuel pump socket, disconnecting the socket and testing for power or voltage.
Since the fuel pump only receives power while in the ON position, go ahead and switch the ignition to the ON position, grab the multimeter black lead wire and ground it to any metal component on your vehicle.
You may also want to ground it on the exhaust pipe. Now, take the red lead and put it on each of the connectors on the socket to check for voltage.
Therefore, if each of the connectors have power, then the pump has power; if not and has no voltage on the connectors, then next you want to look at the inertia switch, this is typically in the trunk.
All you have to do is hit it with anything, like a screwdriver, or your hand, and the red button on top should pop up; when you press it down it will clip and reset.
It is designed to cut the power to the fuel pump in the event of an accident type situation. However, sometimes if you hit a pothole, or junk in the trunk just hits it, it can pop up too.
So if you have no power to the pump, a really fast inspection of the inertia switch may be a quick fix to your problem.
And lastly, you want to check the fuel pressure with a pressure tester kit; you can take the Schrader valve cap off and screw your pressure gauge in.
Once the gauge is, after you turn the key on, you will have actual fuel pressure. The gauge should sit above 30 PSI and sit there.
If you turn the ignition ON and the fuel pressure does not rise, you have a bad fuel pump for sure.
You may say, what if the fuel filter is clogged? With a clogged fuel filter, you would see the fuel pressure rise very slowly or almost not at all?
If you tested for a fuel pump, you will only need common hand tools to do the swap but I would replace the fuel filter also so the pump can work better.
Let’s get started, but first, put on your safety glasses.
Replace A bad or faulty fuel pump
Step 1. Disconnect battery terminal: Take your screw driver and disconnect the car battery’s negative terminal so that you will not have any power going to the car because if you grind something on the car by accident, it won’t spark to ignite the fuel.
Tip: You might want to do a little research about your car. You might want to go to the car trunk and lift that carpet and get access to the top of the fuel tank under the rear seat before you drop the tank.
Step 2. Block off the rear wheels: park the vehicle on flat ground and block off the wheels.
Step 3. Empty the gas tank: Open the gas tank cover and empty the fuel from there. Try to remove as much gas as you can so that the tank is as light as possible.
Step 4. Disconnect the fuel tank input hose: Slide under your car and disconnect the big hose from the gas door to the tank.
Step 5. Disconnect the Fuel lines: Depending on your car make and model, the fuel line may run directly from the fuel tank to the filter. You will need to disconnect the lead and return the hose so that you won’t have a problem when you lower the tank.
Step 6. Set tank in place with jack: Now you are able to use the jack to set the tank in place. Use the jack to set the tank in place evenly. Make sure to push it lightly against the tank because when you remove the bolts holding the tank in place, you do not want the tank to just fall.
Step 7. Remove the gas tank bolts: There are usually 2-4 bolts that hold the gas tank in place. You will want to remove them one at a time.
Step 8. Slowly lower the jack: You will want to very slowly lower the gas tank, and once the gas tank is about halfway down, you will want to hang the gas tank and still remove any more fuel lines or wires while hanging. If everything is disconnected, you can drop the gas tank completely.
Step 9. Remove the fuel case cap: You will want to remove any bolts that hold the fuel case with the filler neck of the tank.
Step 10. Remove fuel pump assembly: You will want to do this carefully, as you take off the fuel pump assembly from the gas tank. There is a lead and return hose, a fuel strainer, the fuel pump attached to it, and a gauge regulator that indicates how much gas is in the tank.
Step 11. Replace the fuel pump: After you remove the assembly and take apart the fuel pump, there are two ways to replace the pump. First, you can replace the entire assembly with a new pump, or just the fuel pump itself (which is likely the whole cause of the issue).
Choose the option that you want to go with and get it mounted back as “nice and smooth” as you can. If you choose just to replace the pump, remember to replace the strainer as well!
Once you’ve done that, it’s putting the assembly back to the tank and the reverse procedure! Pay attention to the arrow on the fuel filter when you’re putting it back. Fill the tank back up with the fuel we previously removed.
Step 12. Start the car: You will obviously want to start it up and make sure it does. You should be feeling pretty confident as to diagnostics stated it was a poor fuel pump, but you still have to check.
When you change a fuel pump, you want to have the ignition switch turned to the run position, shut it off then turn to the run position (to do this a couple of times).
What this process does, is I pressurize the fuel and fill the fuel lines with gas, because we emptied the fuel when we changed the pump. You can now start the car. Awesome! This is it and now you know the whole process of diagnosing and replacing a bad fuel pump.
FAQs.
Q: What happens when the fuel pump is faulty?
A lousy fuel pump with low pressure will disrupt the air-fuel mixture ratio, leading to several performance issues.
Aside from the engine won’t start, you will experience other issues like loss of power under stress, loud whining noise from the gas tank, low gas mileage, engine sputtering, car surging, stalling at high temperatures, and hard starting.
Q: What does a bad fuel filter sound like?
A clogged or dirty fuel filter may cause pressure in the engine to drop, resulting in an inappropriate air-fuel mixture ratio.
Should you hear a knocking or ticking sound when the engine is warmed up, it may be an indication of a clogged fuel filter. This is one of the most noticeable symptoms of a bad fuel filter.
Q: Can you jump-start a car with a bad fuel pump?
Jump-starting a car is typically associated with a dead battery or lousy Kickstarter. It will not make a failed fuel pump start working.
If you’re experiencing failed fuel pump symptoms, I recommend doing a thorough diagnosis of the fuel system to diagnose a lousy fuel pump.
Final word
All internal combustion engine-equipped cars have fuel pumps in one form or another. Most fuel pumps are manufactured to last longer than others. In any case, as the vehicle covers a few hundred miles, the fuel pump may require replacement.
If you notice any of the bad fuel pump symptoms above, or you suspect engine running lean issues, you have to diagnose or contact your mechanic to diagnose and determine if the fuel pump needs replacement.