In order for the internal combustion engine in your vehicle to run, it needs to be supplied with a constant influx of fuel. This requires fuel to be transported from the fuel tank to either the fuel injectors or carburetors, depending on the type of vehicle you have. In pretty much every roadgoing car, the fuel pump is the component responsible for moving gasoline or diesel from the fuel tank to the engine.
Function of a Fuel Pump
A fuel pump is a mechanical or electro-mechanical component of the fuel system that moves fuel from the fuel tank to the engine, specifically to the carburetors or fuel injectors, which disperse fuel into the combustion chambers of the engine. Fuel pumps are either mechanically or electrically powered.
Mechanical fuel pumps are typically gear driven off of one of the camshaft gears. As such, they are typically located under the hood near the front of the motor. Mechanical fuel pumps are most common on older vehicles, particularly vehicles with carburetors. Over time, mechanical fuel pumps gave way to electric fuel pumps due to improved fuel efficiency and demand for higher fuel pressures.
Unlike mechanical fuel pumps, electric fuel pumps do not require a mechanical connection to the engine in order to pump fuel. For this reason, they typically offer improved fuel economy. Another advantage of electric fuel pumps is that they can be optimized to provide significantly higher fuel pressures, which are required for modern fuel injection systems and direct injection systems. A final advantage is that since they don’t require a mechanical connection, they can be located more flexibly. Often, manufacturers will place electric fuel pumps inside the fuel tank.
Common Symptoms of a Bad Fuel Pump
The fuel pump performs a relatively simple task, and because of this, a faulty fuel pump typically presents with a pretty limited set of symptoms. The most common faulty fuel pump symptoms are as follows:
Whining / Chatter / Buzzing – Most fuel pumps run quietly inside the fuel tank or under the hood. Over time, if the bearings within the pump wear, the typical slight hum of a fuel pump can progress into a loud buzzing, whining, or chattering sound. If you start to notice that your fuel pump is making more noise than usual, it’s likely time to replace the pump.
Difficulty Starting Engine – A faulty fuel pump can often fail to supply sufficient fuel to the engine. One of the easiest times to notice this is during vehicle startup. If your car takes more cranks to turn over the normal, sputters on startup, or is otherwise temperamental when you start your vehicle, the fuel pump is one of the prime suspects (as is a clogged fuel filter).
Rough Running – Once the engine is running, a bad fuel pump may not provide enough fuel to keep the engine running well, especially under heavy throttle. Under-fueling a vehicle can create a lean running condition that can result in rough running. Misfires, loss of power, poor acceleration, lower fuel efficiency (fewer miles per tank), and even engine stalling can occur. The fuel pump is often responsible for poor engine running, however there also can be other culprits such as worn spark plugs or clogged fuel injectors to name a few.
Replacing a Fuel Pump
When it comes to replacing a fuel pump, mechanical fuel pumps tend to be pretty straightfoward as they are usually easily accessible under the hood and have very few connections and fasteners. Electric fuel pumps, which are sometimes located in the fuel tank, are often times more difficult. For that reason, we will focus on replacing an electric fuel pump.
Note: The example steps below are intended for general informational purposes solely to help give you an idea of project difficulty and tools required. As all cars are engineered differently, repair procedures and safety hazards vary from vehicle to vehicle. To ensure that you have a vehicle specific repair procedure and an exhaustive list of potential safety hazards, we advise you reference a factory service manual for your vehicle. Similarly, referencing a repair manual such as Chilton or Haynes might serve as a less expensive alternative.
Step 1 – When working on a fuel system, always ensure that your work space is well ventilated and free of ignition sources (e.g. light bulbs, cigarettes, electronics, static electricity from clothing, heaters etc). Make sure to avoid accumulation of fuel vapors which could prevent a fire hazard. Additionally, don a good pair of safety glasses to ensure that you protect your eyes and take care not to inhale fuel vapors while you work.
Step 2 – Depressurize the fuel system. This can usually be accomplished by removing the fuel pump fuse, and running the engine until it dies (which occurs once all the fuel in the fuel lines has been consumed). It should be noted that some fuel systems are under extremely high pressure (in excess of 2000 psi for some direct injection systems) and failure to depressurize properly and safely prior to starting disassembly can present significant safety risks. Make sure you thoroughly understand these risks and how to avoid them before continuing. For these types of high pressure systems, consult a factory service manual.
Step 3 – Disconnect the battery cable from the battery’s negative terminal. This usually requires an adjustable wrench. Take care as there is risk of shock that can result in injury or death if you complete the circuit with your hands or your tools.
Step 4 –Determine where your fuel pump is located and how to gain access to it. Some vehicles may require the fuel tank to be removed from the vehicle to access the fuel pump. Others may have a simple access panel under a rear seat or in the trunk of the vehicle.
Step 5 – If you need to remove the fuel tank from the vehicle, you will likely need to drain the tank, remove the straps holding the tank in place, disconnect the fuel lines, disconnect the fuel filler hose, and disconnect the electrical connections at a minimum. There may be other components such as the fuel level sender that you also need to address.
Otherwise, after ensuring you have provided adequate ventilation, you may remove the cushion on the back seat to expose the access port on the top of the fuel tank for your fuel pump. Remove any electrical connections, hoses, etc that are attached to the fuel pump. You will likely need a set of screwdrivers to remove the hose clamps. Most other components can be removed with a good ratchet or combination wrench. Even if you don’t have to remove the fuel tank, this process is a bit easier when the vehicle has little to no fuel in the tank.
Step 6 – Remove the fuel pump from the tank. There may be a retaining ring that needs to be rotated to allow the pump to be removed from the tank, or a series of fasteners. If you leave the fuel tank unattended with no fuel pump for more than a minute or two, cover the hole in order to avoid accumulation of fuel vapor as well as to avoid getting contaminants in the tank which could potentially clog the fuel filter.
Step 7 – Verify your replacement pump is a match to the pump you just removed. It should fit and connect in a similar manner to the pump you just removed from the fuel tank. If it is correct, install the new pump by reinstalling components in the reverse order that they were removed.
Step 8 – Reconnect all remaining components, install the fuel tank back in the vehicle if necessary, and replace the rear seat cushion. Reinstall the fuel pump fuse and battery cable.
Step 9 – At this point, you are ready to start the vehicle. Since the fuel system has been depressurized, it may take a few seconds before the vehicle turns over as the fuel has to travel all the way through the lines before it reaches the motor. If you notice any fuel leaks, stop, find their source, and repair them immediately before driving the vehicle.
Best Fuel Pump Brands
When it comes to selecting a high quality replacement fuel pump, there are tons of options out there. The following are the brands we’d recommend based on our experience due to their consistent quality and overall value.
Bosch is a brand that makes a wide array of parts ranging from sensors to ignition components to fuel system components. They are used throughout the entire automotive industry by almost every car manufacturer in some capacity. As you can likely imagine, any automotive parts manufacturer that is as widespread as Bosch must be so for good reason. That reason is because Bosch makes high quality parts that are fairly priced. Bosch’s fuel pumps are great, and you can’t go wrong should you choose to install one on your vehicle.
Click here to find a Bosch fuel pump for your vehicle.
Spectra offers a vast array of fuel pumps for a variety of automobile manufacturers. They are consistently high in quality and well priced, making them a high value proposition for your next fuel pump replacement project. Spectra fuel pumps are widely available at online retailers which makes them convenient as they can save you a trip to the auto parts store. Overall, we are confident you’ll be in good shape when using a Spectra fuel pump and can recommend them accordingly.