The fuel pump’s main function is to push fuel from the gas tank to the engine with help from other parts of the car. Because of this, it can be difficult to know if it is failing or even if you have symptoms of a bad fuel pump.
The most important piece of diagnosing a vehicle is realizing how it works, behaves and runs each day. Does it make a sound when it runs? If yes, what sound does it make? What is the vehicle’s normal running RPM?
With this article and your attention to details, you’ll be able to easily identify fuel pump issues and know what to do to fix them.
The first step to knowing if there is an issue is knowing if your vehicle has hard starting, less power, or is struggling to idle smoothly, etc.
Many vehicle components are interdependent and connected so diagnosing could be a hard task at times. The process can be trial and error and often takes asking for and getting assistance from a professional and needing to be aware of the details.
What Is A Fuel Pump?
The fuel pump moves gasoline from the tank to the engine. It pumps fuel from the tank through tubing to the injection system. In turn, the fuel will be injected into the engine for combustion with air.
Usually, older vehicles will have a different design, however, the fuel pump is still moving gas. In older cars, fuel can be sent to the carburetor.
There are different types of fuel pumps even though the basic functionality will be the same. Your vehicle may have a high-pressure mechanical or electrical pump.
How Does a Fuel Pump Work?
Mechanical fuel pumps used to be common, sometimes located externally to the fuel tank. In terms of electronic fuel injection, a mechanical pump is now obsolete, having been replaced by an electric fuel pump, typically located inside the fuel tank.
The pump creates positive pressure that sends fuel up the gas lines to the engine. In the tank, the pump is submerged in cool liquid far away from the engine, making igniting it in an explosion less likely.
A modern fuel pump consists of a direct-current (DC) electric motor that draws fuel from the tank. The pump sends fuel through the fuel injectors to mist it into the cylinders, where it mixes with air, and a charge from the spark plugs combusts.
A filter located on the pump’s intake sifts impurities to prevent them from entering the fuel lines to contaminate your engine.
On the whole, the electronic fuel pump provides multiple benefits, one being it enables less fuel consumption via continuous metering from the vehicle’s electronic control unit (ECU). A second benefit is the predelivery of fuel, since RPM of the engine are no longer used to operate the pump.
This predelivery allows new vehicles to use auto start and stop systems, saving fuel since the engines can stop and restart while not idling instead of the engine remaining at a continuous idle.
Where Is The Fuel Pump Located?
Fuel-injected vehicles have a fuel pump inside the tank, and if you have gasoline direct injection (GDI), you have another pump near the fuel rail.
Most fuel pumps are an entire assembly with a float and sensor inside. The pump pulls the fuel through a filter located near the bottom of the tank and supplies it to the outlet tube and to the engine.
In GDI systems, the primary pump pumps the fuel and supplies it to the second pump at the fuel rail. The second pump is driven by the camshaft which compresses and pressurizes the fuel.
Symptoms Of A Bad Fuel Pump
The fuel pump is responsible for supplying fuel to the engine to run, and when it starts failing, it will lead to performance and drivability issues. You need to look for the following signs of a bad fuel pump that is signaling to the driver that there is a serious problem.
#1. Hard starting.
An associated common problem with a failing fuel pump is hard starting. The fuel pump can weaken/wear over a period of time, and since it runs continuously when the switch is in “on” position while the ignition is running, this can happen.
A bad fuel pump can still deliver fuel, but it may start hard due to a lack of supply. A bad fuel pump may result in the engine having to crank longer than normal or crank a zillion times to start it.
#2. Engine Surging.
A failing fuel pump will cause a vehicle to surge indicating the fuel pump needs to be replaced. Surging will occur at a random constant speed and if it happens regularly, it would be due possibly to a bad fuel pump.
#3. Frequent stalling at high temperature.
Frequent stalling indicates low fuel pump pressure. It can be caused by a multitude of problems in a car, but it is important when you are stalling regularly at a high temperature. A normal, functioning car should not stall at high temperatures.
If you stall over and over again as the engine temperature rises, then you can verify for certain that you will need to replace the fuel pump.
#4. Engine stuttering.
A stuttering engine is one of the surest signs of a bad fuel pump – usually at a high speed. If you see an engine suddenly stutter at a high speed and go back to running normal, that is an indication of a problem with the fuel pump.
This could also be a sign of a fuel injector failing as well. This means that either the fuel pump or fuel injectors are not letting enough fuel into the engine at the proper pressure. You have to survey the fuel pump and fuel injectors and narrow down what the exact problem is.
#5. Low gas mileage.
Low gas mileage could indicate bad fuel pump symptoms 6.0 Powerstroke. If you are noticing that you are filling up the gas tank more than you used to, it could be due to a bad fuel pump.
There may be some internal valve inside the fuel pump that has sized and the fuel pump is expelling more than the engine is requiring. That can create another problem in the engine if it is expelling more fuel.
#6. Loss of power under stress.
Poor fuel pumps in diesel or petrol-powered engines may exhibit loss of power when under stress, i.e. carrying too much weight while accelerating, or uphill. The engine can stall because the fuel pump cannot supply the demands of the engine system.
In this case, the power can’t go where it needs to go or, the vehicle cannot move at all. If the fuel pump is at fault, it means that this is the stage where it cannot accurately regulate or export sufficient fuel to the engine system.
#7. Whining sound from the gas tank.
One of the best fuel pump symptoms of the Honda Accord or any auto vehicle model, is one that is loud enough and has a whining sound.
The car may produce a very loud howl or whine if the fuel pump is deteriorating or weak, while it is running. Usually, a normal fuel pump exhibits a humming sound which signals that it works as designed.
In contrast, any loud whining emanating from the gas tank is a sign that the fuel pump is failing, or it is signifying that the fuel level is at least low (you might be less than ¼ of a tank), or that you have water in the gas tank.
#8. Car will not start.
A more severe symptom of a bad fuel pump is obviously having a vehicle that will not start. If the fuel pump totally fails, it could be to a point of not providing any pressurized fuel which could break a fuel vacuum; the vehicle will refuse to start.
The vehicle engine can still revolve like it usually does when you turn the key, only it will be unable to start due to low or totally no fuel pressure. There are many different causes of a vehicle not starting; therefore, it is prudent to diagnose your car if you have such symptoms.
#9. Increased engine temperature.
If the fuel pump malfunctions and does not export the right quantity of gas needed by the engine system, the engine will become overstressed and could cause a managed rise in temperature.
You also want to look at your gas strainer, as this could be characteristic of a half functioning fuel filter.
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.
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 are the signs of a bad fuel pump?
If the pressure from a bad fuel pump is low, it will throw off the air-fuel mixture ratio, which will cause your car to run poorly.
In addition to your car not starting you will experience no power when under stress, strange whining noise from the fuel tank, poor gas mileage, engine hesitation, surging, stalling when hot, or difficult cranking issues.
Q: What does a bad fuel filter sound like?
If there is a dirty or clogged filter, the fuel may not build the necessary pressure for the engine to run, and the fuel may not mix properly in the air-fuel mixture ratio.
If you hear a knocking or ticking sound after the engine warms up, the fuel filter is most likely dirty. This will be the most noticeable symptom of a clogged fuel filter.
Q: Can you jump a car with a bad fuel pump?
Jumping a car typically means a dead battery or poor key-starting activity, The jump will not allow a failed pump to work.
If you have already diagnosed failed pump symptoms, I recommend diagnosis as thoroughly as possible for a bad pump in the entire fuel system.
Q: Can AutoZone test my failed pump?
If you are wondering how to test your pump, you might think it will be complicated, but testing fuel pressure is much easier with AutoZone on your side.
Stop by AutoZone for a fuel pump pressure tester kit, and you will easily check your pump and the full air-fuel system. AutoZone even provides an adapter should your vehicle be without a Schrader valve testing port on the fuel system, and full instructions.
Final word
Every internal combustion engine car has a fuel pump in one form or another. Most fuel pumps are made to last longer than others. Regardless of the type of fuel pump, if a vehicle has traveled several hundred miles, it will eventually need to be replaced.
If you notice any of the bad fuel pump symptoms stated above or you have even a suspicion of engine running lean issues, you have to diagnose the problem yourself or have a mechanic diagnose and determine if the fuel pump needs to be replaced.