Mercedes-Benz of Stevens Creek - 2047
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Mercedes-Benz of Stevens Creek - 2047

Mercedes-Benz C 300 Fuel Pump Problems - How To Troubleshoot and Fix

What Is A Fuel Pump?

Electronic fuel injection systems work in sync with your fuel pump regulator to deliver fuel based on vehicle output. A fuel line starts at your fuel tank, which uses a pump to draw fuel from the fuel tank to your engine. It also delivers low-pressure fuel to your carburetor. With electric fuel injection systems, positive electrical pressure is used to drive fuel from the fuel lines to your internal combustion engine.

A fuel pump is like the heart of the Mercedes-Benz C 300. It is responsible for delivering gas from your fuel tank to your engine. Steady fuel pressure is extremely important because it ensures the engine receives the right amount of fuel based on driving conditions. Sudden acceleration or driving up inclines requires a bit more power, something a working fuel pump can provide.


Mercedes C 300 Fuel Pump Location

Your fuel pump is located inside of your Mercedes-Benz C 300's gas tank.


Common Symptoms Of A Bad Fuel Pump

Whining or Howling Noises From The Gas Tank

A worn-out fuel pump tends to produce a loud, high-pitched whine when the engine is on. When driving at higher speeds, you may notice sputtering sounds coming from your engine due to a lack of proper pressure of fuel going to your internal combustion engine.


Loss Of Power

A defective fuel pump generally leads to a loss of power. Less pressure in your fuel line means your engine is getting inconsistent gas volume, especially with sudden changes in acceleration or elevation. Engine misfires can also occur due to a lack of fuel or fuel pressure, resulting in jerky acceleration from a full stop, stalling, and other irregularities.

Note, this type of acceleration can also be due to a defective throttle gas pedal position sensor.


Check Engine Light Turns On

If your check engine light turns on, use a diagnostic scanner to read your Mercedes-Benz C 300's fault codes. There are many solid recommendations online on diagnostic scanners that work well with the Mercedes-Benz C300, or you can ask your certified Mercedes-Benz technician to help you with this.


Loss Of Fuel Economy

Bad fuel pumps may also cause your Mercedes-Benz C 300 not to start. At this point, your fuel pump is defective enough where it is not providing fuel for your engine at all.


How To Check Your Mercedes C 300's Fuel Pressure

Using a fuel pressure gauge will allow you to see if enough pressure is being produced for gas from the fuel tank to reach your engine. It is a very simple procedure.

  1. Open your Mercedes C 300's hood and remove the engine cover.
  2. Lift off the Schrader valve cap from the fuel pressure port on the fuel rail.
  3. Connect a compatible fuel pressure tester to the fuel test port.
  4. Turn the vehicle on without cranking the engine.
  5. Look for a normal fuel pressure range of 47 – 55 PSI on idle. If your vacuum hose is disconnected, PSI readings vary slightly with an acceptable range of 54 – 61 PSI.


How To Change Your Fuel Pump

Fixing the common problems associated with a faulty fuel pump involves diagnosing and replacing the part as soon as you detect an issue with starting, running, or repeated stalling while accelerating.

Here are the steps needed to replace your fuel pump.

  1. Using a pair of safety goggles, completely drain your fuel pump to avoid spilled fuel and strong vapors.
  2. Disconnect your negative battery cable and remove your rear seating to reveal the integrated floor access cover.
  3. Once you see the pump assembly, disconnect all fuel hoses, emissions hoses, and connections.
  4. Remove your pump assembly's retainer ring to loosen it, wiping dirt and debris from your pump access hole to keep the inside of your tank clean.
  5. Remove the fuel pump.
  6. Align your new replacement fuel pump to your assembly, mounting your seal ring in place.
  7. Connect all fuel hoses, emissions hoses, connections, and re-mount your floor access cover and rear seat cushions.
  8. Reconnect your negative battery cable, re-fuel, and perform a test drive to catch any aforementioned issues.

If out on the road, drivers should pull over and visit a certified Mercedes-Benz technician immediately for diagnosis. Note, unlike fuel filters, fuel pumps do not have to be replaced at regular intervals. However, high mileage makes them more prone to wear and tear. Get a new Mercedes-Benz fuel pump here when it is time for a replacement. As a best practice, Mercedes-Benz C 300 drivers can avoid strain on their pump by filling up the fuel tank with every visit to the gas station and checking for clogged fuel filters.