The fuel pump is a critical element of your Mercedes-Benz S-Class. The fuel pump is aptly named as it is the component responsible for literally pumping your car’s fuel from its tank to an engine. As you can imagine, a malfunctioning fuel pump will almost always lead to a complete disaster. For this reason, it’s important to understand not only the function of a fuel pump but also the common symptoms of a malfunctioning pump so that you may take preventative measures before a catastrophe happens.
What is a Fuel Pump?
Any vehicle with an internal combustion engine needs a fuel pump that pushes fuel from the tank to the engine. When you turn on the key, you essentially activate and pressurize the fuel pump, which you can hear as a hum or quiet whine in your Mercedes-Benz S-Class sedan. In most modern vehicles, fuel pumps are electric pumps mounted in the fuel tank. However, some cars are equipped with mechanical-style or inline fuel pumps. In most cases, fuel-injected engines use electric fuel pumps located inside the fuel tank, whereas carbureted engines use low-pressure mechanical pumps located outside the fuel tank.
Fuel Pump Failure
Because the function of the fuel pump is so important, any issues with it can cause major performance and drivability problems. In almost all cases, a failing or bad fuel pump will produce a few symptoms that will alert you of a potential problem. If you notice one or more of the following signs of fuel pump failure, it’s important to check out your system before you’re left on the side of the road with a car that just won’t start.
1. The engine makes sputtering noises at high speeds.
One of the most common early signs of transmission problems happens when you travel at consistently high speeds. As you drive, you may notice that your car runs fine for 10 or 15 miles before it begins to sputter or jerk. Although some people will assume this sputtering is due to an almost empty tank, bad gas or another fuel-related problem, it’s also not uncommon for a worn-out fuel pump to cause the same effect. It means that the fuel pump is struggling to supply fuel to the engine at the right pressure, and it’s this loss of pressure that leads to the sputtering.
2. Your car loses power when you accelerate.
Have you noticed that your S-Class sedan jerks as you accelerate from a stop? You may notice a stalling sound before the car is able to smoothly accelerate. Once you remove your foot from the brake and apply the gas, a working fuel pump increases the flow of gas, allowing you to accelerate. However, in the case of a non-working fuel pump, your car doesn’t have the power it needs to accelerate. Once the car can restore the pressure, your engine runs smoothly and you can go on your merry way.
3. You notice a sudden loss of power when your car is under strain.
When your car tries to complete an ordinary task like traveling forward, it can be put under stress if it is hindered by outside forces. For example, this might happen when you’re hauling a load or when you’re climbing a hill. If your car begins to sputter, can’t accelerate or loses power, it could mean the fuel pump is to blame. Although even an older fuel pump can usually maintain a steady stream of pressure and fuel under normal conditions, these devices fail or create resistance when under stress.
4. Your car is surging.
If the power of your vehicle is fine when you’re driving, you may notice that it suddenly accelerates with no drive input--a process known as “surging.” Although some drivers may attribute surging to a malfunctioning fuel filter, believing it’s not properly trapping rust and dirt, it’s more likely that surging is due to the fuel pump suffering irregular resistance inside its motor. This can happen either as the result of normal wear-and-tear as well as age. In this situation, the fuel pump fails to pull enough electricity to maintain the pressure you need to travel at a steady speed and may jolt forward as the pressure increases.
5. The engine just won’t start.
The last symptom of a fuel pump failure is also the most critical. If you ignore other warning signs of a bad fuel pump, you’ll almost certainly end up here--on the side of the road with a car that won’t start. If your fuel pump has failed to the point where it won’t start your car, it essentially means that fuel is not getting to your engine. You’ll hear sparks as the engine tries to ignite, but there won’t be any fuel there to burn. If you believe this is the case with your S-Class, check for pressure in the fuel line and a blown fuse.
Although the cost of replacing a fuel pump in a Mercedes-Benz S-Class sedan varies, most drivers can expect to pay between $478 and $591 for the job. Parts are priced between $390 and $480, and if you choose to hire a mechanic to do the work for you, you could be looking at $88 to $111 in labor costs.
Nearly all modern vehicles that use internal combustion engines are equipped with fuel pumps. This is the component that is responsible for pumping fuel from your gas tank to your engine at the exact pressure needed to meet the performance demands of your car. Although most fuel pumps are built to last, as the vehicle enters higher mileage, it is not uncommon for your Mercedes S-Class pump to require replacement. If you believe your fuel pump is having an issue because you’ve noticed a loss of power during acceleration, sputtering at high speeds or an engine that won’t start, it’s important to inspect it as soon as possible to determine whether you should replace the component.