(Updated on February 24, 2023)
The fuel pump is a valuable component of the internal combustion engine. Since there needs to be a mixture of fuel and air inside the combustion chamber, the fuel pump is responsible for pumping fuel from the gas tank, through the fuel lines, and into the combustion chamber.
What is a Fuel Pump?
A fuel pump is a simple electromechanical device that transfers fuel from one location to another.
In most cars, fuel from the gas station is pumped into a gas tank that sits at the rear of the car, even though that fuel is needed in the engine at the front of the car. When you turn on the car, the fuel pump pressurizes the fuel system, which brings fuel toward the front of the vehicle.
The pump is usually located in the fuel tank and submerged in fuel. The surrounding fuel cools the fuel pump during operation.
Some vehicles have another pump located along the fuel line or even in the engine bay to further pressurize the fuel. For instance, direct injected vehicles require a secondary high pressure fuel pump to bring fuel pressure from 60-80 psi up to around 2,000 psi or even more.
The fuel lines won’t be over pressurized as long as the fuel pressure regulator is working. Before the fuel is pushed into the fuel injectors and shot into the cylinders at precise amounts, it goes through a fuel filter to remove any contaminants.
Older vehicles may use a mechanical pump, which uses a plunger or diaphragm to create suction that moves the fuel to the carburetor and then to the injectors.
Newer vehicles with electronic fuel injection have higher pressure needs which can only be supplied by electric pumps.
Why Do Fuel Pumps Fail?
With proper care of the fuel system and good fuel, a fuel pump should last at least 100,000 miles, and sometimes several times that. There usually isn’t a regular maintenance interval, though you can always check the owner’s manual just to be sure.
1) Age-Related Degradation
Even with the best care, most parts will eventually wear down and break. This isn’t an inherent fault of yours or the manufacturer’s; most components are built with a specific service life in mind.
2) Bad or Improper Fuel
Not all fuel is created equal. Besides choosing the correct octane rating of gasoline, it’s a good idea to select a good gas station for the best chance of having quality fuel. While any station can have a batch of bad gas, it may be more likely at some than at others.
Contaminants or water in the fuel can clog the fuel filter which puts more stress on the fuel pump.
In the same way, be careful of additives for the tank. Use only well-known and mechanic-recommended fuel system additives.
Using the incorrect type of fuel is a quick way to cause problems with the fuel pump. Never put diesel into a gasoline-powered vehicle, or vice versa. This is a good way to destroy your fuel system and potentially the engine.
Running ethanol in a vehicle that was not designed for it may cause problems with the fuel pump depending on the concentration. Low concentrations of ethanol (about 10%) are present in most modern fuels. E10 gasoline is compatible with most modern gasoline fuel systems.
Related: Ethanol vs Non-Ethanol Gas (Comparison)
3) Driving on an Empty Tank
It’s important to drive the vehicle with at least 25% of the tank full in order to properly cool the fuel pump. If you drive around frequently with less fuel than this, the fuel pump is in danger of overheating damage.
When the fuel level is low, you are more likely to draw sediment from the bottom of the tank. This could saturate the fuel filter with buildup prematurely, or the sediment could even get transferred into the fuel pump itself.
Symptoms of a Bad or Weak Fuel Pump
Many of these symptoms are shared with other failing components in the fuel system. You may have to do some testing or diagnostics to determine which fuel system component needs to be replaced.
1) Difficulty Starting Vehicle
If you crank the ignition but the car won’t start, or it starts and immediately dies, make sure you can hear the fuel pump turn on when you first turn the key to the “ON” position. Most fuel pumps make an audible buzz as the pump primes the fuel lines when you go to start the car.
Some vehicles will prime the fuel pump when you unlock the car or open the driver’s door. This process varies by manufacturer but is more common on European cars.
2) Stalling (Especially Under Load)
If the engine suddenly shuts off while you’re driving, the fuel pump may be dying. It’s inconvenient to stall at a stoplight while other drivers honk at you, but it can be downright dangerous to completely lose power in the car while driving on the freeway. The vehicle should be examined by a mechanic as soon as you are able to do so.
If the car drives fine under normal conditions but stalls while it’s under load (such as when you step on the gas or haul something heavy), a failing fuel pump may be causing the issue by not being able to keep up with the stress.
3) Sputtering, Rough Running
A coughing engine or general rough running while at idle or driving at low speed can indicate problems with the fuel pump. These can be caused by engine misfires, since cylinder function isn’t balanced.
4) Low Power
Slower acceleration than normal is often noted when merging onto the freeway in cars with bad fuel pumps. The pump simply can’t provide enough output to the engine so the car struggles. Driving uphill will only exacerbate this problem.
5) Engine Surges
If you are driving the vehicle at a constant speed then suddenly the engine revs up, which makes you speed up (despite not pressing harder on the accelerator pedal) the fuel pump may be having issues. If this happens to you, be very careful to keep a large following distance to avoid accidentally driving into the vehicle in front of you on your way to the mechanic.
6) Check Engine Light
Newer cars have a complex system of sensors that should catch the problems with the fuel pump before other more dangerous symptoms take place. Insufficient flow through the injectors will be noted by the computer and should throw a check engine light. Engine misfires should also cause an alert.
If you see a check engine light, it’s best to get the car scanned and fix the issue. Take the car to a mechanic or auto parts store to have the code read by an OBD-II scan tool, which will tell you the issue that caused the alert so that you or your mechanic can further troubleshoot.
7) High-Pitched Whining
If you hear a loud whirring or whining from the back of the car where the fuel tank is located, check the fuel pump. It should normally emit a soft hum which isn’t audible to the driver while the vehicle is in motion.
To perform a very brief check of the fuel pump, you can actually listen by the tank for the fuel pump to operate normally by turning the car ignition to “on” while the fuel door and fuel cap are open. If you hear nothing, your pump is probably toast.
Other Possible Causes of these Symptoms
If you experience some of these symptoms but the fuel pump has been deemed healthy or replaced already, check for the following possible issues.
1) Bad or Clogged Fuel Injectors
These are the final stop for the fuel before it goes into the cylinders. Since that is where the magic happens, fuel injectors that impede the flow of the fuel will certainly cause some problems.
2) Bad Fuse or Relay
Fuses and relays are easy to check and cheap to replace. If you are trying to troubleshoot at home, this is often a great first step.
3) Poor Electrical Connection
Modern systems rely on many sensors and connectors to relay information. A short or bad ground can cause any number of strange issues issues, especially intermittent ones.
4) Clogged Fuel Filter
Just like a clogged fuel injector means the cylinder can’t get the fuel it needs, a clogged filter can restrict the fuel.
5) Out of Gas
Never overlook the simple things. If you have issues with your fuel gauge, you could be low on fuel and not realize it.
Fuel Pump Replacement Cost
As always, the cost of professionally replacing a fuel pump varies largely depending on the make, model, and year of your car, and which mechanic you go to. For an inexpensive vehicle, the pump itself can be as cheap as $50 and labor is usually between $200-300.
More complex and expensive vehicles will probably have a higher cost for both parts and labor. Some of these replacements can cost upwards of $2500.
3 thoughts on “7 Symptoms of a Bad Fuel Pump and Replacement Cost”
Great page. I don’t use my car much and never knew that driving with less than 25% of fuel overheats the pump. It killed two pumps. Now I won’t make the same mistake.
The mechanic tells me I need both a fuel pump and an MAF sensor to solve my car’s intermittent stalling. How likely is it that both are out at the same time?
I don’t know. It’s not uncommon for two components to fail or work intermittently on older vehicles. Did he try cleaning the MAF sensor first, or tell you why those parts were bad?