Common Symptoms of Bad fuel pump : How to Diagnose and Replace?

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. 

Most Common Symptoms of Bad Fuel Pump

Because the fuel pump is responsible for exporting gas to the engine for it to run, it’ll give performance and drivability problems when it starts failing. You have to watch out for the following signs of a bad fuel pump that alerts the driver of a critical problem.

how to test a fuel pump

Hard starting

A commonly associated issue with a faulty fuel pump is hard starting. Over time, the fuel pump can weaken or wear out since the pump constantly runs whenever the ignition is switched on. A lousy fuel pump may still pump fuel, but the engine may experience a hard start due to inadequate fuel supply. A failing fuel pump may cause the engine to take more cranks to start than normal, and in a more severe case, it may take the engine to crank a zillion times before it can start.

Engine Surging

A failing fuel pump may cause a vehicle to surge and show you have to replace the fuel pump. Surging occurs at a random constant speed. If this happens consistently, it is possibly a result of a lousy fuel pump.

Stalling at a high temperature

Stalling indicates a fuel pump low-pressure symptoms. It can occur due to many problems within a car, but you have to pay attention when it happens regularly at high temperatures. Typically, stalling at high temperatures indicates a problematic fuel pump. If stalling continues with rising engine temperature, it tells you you have a fuel pump deterioration and need to be replaced.

Engine sputtering

One of the surest signs of a lousy fuel pump is a sputtering engine – usually at high speed. If you notice an engine suddenly sputter at high speed before returning to normal operation, it indicates there’s an issue with the fuel pump. This can also act as a failing fuel injector symptom. This means the fuel pump or injectors cannot provide adequate fuel to the engine at ideal pressure.  You have to diagnose your fuel pump and fuel injectors and determine the actual cause of this symptom.

Low gas mileage

Low gas mileage could indicate bad fuel pump symptoms 6.0 Powerstroke. If you notice you have been filling your gas tank more than usual, it may be due to a faulty fuel pump. A valve inside the fuel pump may have sized, causing the pump to export more than the engine system’s required fuel amount. Excess fuel in the engine can create another problem in the engine.

Loss of power under stress

Another faulty fuel pump symptom of diesel or petrol-powered engines is the loss of power when the car is under stress, such as carrying heavy loads while accelerating or while driving uphill. The engine may shut down due to the fuel pump’s inability to meet fuel demands by the engine system. In such a case, the vehicle may be unable to go or maintain the required amount of power. If the fuel pump is the culprit, it signifies it cannot regulate fuel accurately and export the required amount of fuel to the engine system.

Whining noise from the gas tank

One of the most noticeable fuel pump symptoms of the Honda Accord or any other vehicle model is a loud whining sound. A failing or weak fuel pump may produce a noticeable loud howl or whine while running. Typically, a normal fuel pump should produce a humming sound that shows it’s working. However, A loud whining coming from the gas tank indicates you have a failing fuel pump – or indicates your fuel level is below ¼, or you have water in the gas tank.

Car not starting

A more serious symptom of a bad fuel pump is a car not starting. If the fuel pump fails wholly to a state of not providing pressurized fuel that can break the fuel vacuum – the vehicle will not start. The vehicle engine will still revolve well when you turn the key but will not start due to low fuel pressure or no fuel at all. Many other factors can cause the car not to start, so diagnosing your car when you face such issues is highly recommended.

Increased engine temperature

Should the fuel pump fail to export the right amount of gas required by the engine system, this could overstress the engine, resulting in an irregular rise in temperature. You also want to inspect your gas strainer, as this could be one of the symptoms of a bad fuel filter.

How to diagnose and replace a bad or faulty fuel pump

Before you replace the fuel pump, you want to check a few things once you notice any of the symptoms above. I will show you how to check it just In case it isn’t the fuel pump that is bad and it’s something a lot easier to fix.

bad fuel symptoms

So the first thing you want to do is grab your key, put it in the ignition, and turn it to the ON position. Listen for a hum or whine sound from the rear of the car. Suppose you didn’t hear any sound; that doesn’t mean the fuel pump is bad. It could result from a bad relay or blown fuse you must replace.

Grab your owner’s booklet and flip through till you get the page about fuses and learn where to locate the fuel pump fuse. You want to pull out the fuse and visually inspect the fuse. Grab your multimeter and check the voltage on the fuse holder. The normal voltage should be around 12:00.

You may want to check if the fuel pump is getting power. Locate the fuel pump socket, disconnect the socket, and test the voltage. Since the fuel pump only received power at the ON position, switch the ignition to the ON position, grab the multimeter black lead wire, and ground it to any metal component of your car. You may want to ground it on the exhaust pipe. Now, grab the red lead and check each connector on the socket to see if there’s a voltage.

If all the connectors are getting power, it means the fuel pump is getting power as well. But if you don’t get voltage on the connectors, the next thing you want to check is the inertia switch. It is usually located in the trunk. All you have to do is hit the switch with a screwdriver, and the red button on top will pop up. Then, you should press it down, and it will clip and reset.

This switch is designed to cut the power in the fuel pump in case there is an accident. But sometimes, it can get triggered when you hit a pothole or junk in the trunk just hit it. So, if power is not reaching the fuel pump, real quick, inspect the inertia switch because that might be a quick fix to your problem.

There’s one more thing to check, and that’s to test the fuel pressure using a pressure tester kit. To do this, you have to take off the Schrader valve cap and then screw in your pressure gauge. With the gauge connected, you will get the actual fuel pressure when you turn on the key. The gauge should give you at least 30 PSI, and it should stay there. Suppose you turn the ignition to the ON position and the fuel pressure does not rise – it indicates you have a faulty fuel pump for sure.

You might ask – what if the fuel filter is clogged? If the fuel filter is clogged, you will see the pressure rise slowly or rise just a little bit. If your testing proves you need a fuel pump replacement, you will need common hand tools. You also want to replace the fuel filter so the fuel pump will run efficiently.

Now, let’s get started. First, grab and put on your safety glasses.

Step 1. Disconnect battery terminal: Grab your screwdriver and disconnect the car battery’s negative terminal so that you don’t have any power over the car. That way, if you grind something on the car by mistake, it won’t spark and ignite the fuel.

Tip: Do a little bit of 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 or 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 from moving.

Step 3. Empty the gas tank: Open the gas tank cover and empty the fuel from there. Remove as much gas as you can to make the tank as light as possible.

Step 4. Disconnect the fuel tank input hose: Slide under your vehicle 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. Disconnect the lead and return the hose so that you won’t have a problem when you lower the tank.

Step 6. Support the tank with a jack: With the fuel lines disconnected, grab your jack and slide it under the tank, and jack it to support the tank. You have to evenly balance it and lightly press it against the tank so that when you lose the bolts holding the tank, it won’t just fail.

Step 7. Unbolt the gas tank bolts: there are usually two or four bolts holding the gas tank. You have to remove them one at a time.

Step 8. Lower the jack: Slowly lower the gas tank. With the gas tank halfway down, you have to hang it and remove any remaining fuel lines or wires. With all hoses disconnected, you can drop the gas tank completely.

Step 9. Pull off the fuel case cap: Unbolt the bolts holding the fuel case with the tank.

Step 10. Take off the fuel pump assembly: Carefully take off the fuel pump assembly from the gas tank. The fuel pump assembly has a lead and a return hose, a fuel strainer, the fuel pump itself attached to it – and the gauge regulator that indicates the gas level.

Step 11. Replace the fuel pump: there are two ways to do this. First, you can get rid of the old fuel pump assembly and replace it with a nice one or get a new pump since it’s the only thing that is bad in the assembly. Choose the option you want to go with and make everything nice and smooth. If you choose to replace only the fuel pump, remember to replace the strainers as well.

And that’s it! Put the assembly in the tank and follow the reverse procedure. Pay attention to the arrow on the fuel filter, which indicates the flow area while installing it back. Once you’re done with the installation, refill the tank with the fuel you removed earlier.

Step 12. Start the car: you want to see if the car starts up. You should be pretty confident because the diagnosis pinpointed the fuel pump. When you change a fuel pump, you want to turn the ignition to the run position, shut it off, and turn it to the run position – do this a couple of times. What that does is pressurize the fuel and fill the fuel lines with gas because you emptied it when you replaced the pump. Go ahead and start the car. Awesome, and this is it. This is how you diagnose and replace a bad fuel pump.


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.

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.

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.

Can AutoZone test my failed pump?

If you wonder how to test a fuel pump, you might assume it’s a difficult task. With AutoZone at your aid, checking fuel pressure is a lot easier. Grab a fuel pressure tester kit from AutoZone and check your fuel pump and your entire fuel system. AutoZone includes an adapter to help you in case your vehicle does not have a Schrader valve tester port and instructions on how to use the kit.

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.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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