In modern Mercedes-Benz automobiles the fuel pump is electric and located inside the saddle-fuel tank. The fuel pump creates positive pressure in the fuel lines, pushing gasoline to the fuel rail, where the DME controls fuel flow to the engine via a programmed fuel injection map. In tank fuel pumps have many benefits. The fuel is submerged in fuel keeping it cool, preventing vapor lock and electrical issues. The fuel pump delivers a constant flow of gasoline to the fuel pressure regulator, located in the left side of the fuel tank. The fuel then flows to the fuel rail at a regulated pressure and volume.

A faulty fuel pump can cause poor engine performance and hard starting problems. When they fail completely you may be left with an engine that doesn't start. If you suspect your fuel pump has failed, you can confirm the fuel pump is received the correct voltage when commanded ON by the fuel pump relay using a digital volt ohm meter (DVOM). See our tech article on fuel pump testing.

Replacing the fuel pump on a W211 can be done without removing the fuel tank. The fuel pump is located in the right side (passenger side) of the fuel tank. There is an access panel below the passenger seat cushion. Even though the fuel pump is located in the right side of the fuel tank, the electrical connector is on the left side, under the access panel for the fuel filter. When replacing the fuel pump, all work will be performed on the right side of the tank.

Remember that your car may have been serviced before and had parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve, as they grow older. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

It is best to replace your fuel pump with the fuel tank drained. This reduces the amount of possible spilled fuel and fuel vapors. When replacing, work in a well ventilated area. Working outdoors is a good choice. Do not use incandescent work lights or power tools. Fuel and fuel vapors are highly combustible.

Drain your fuel tank. Run the vehicle for about 20 seconds. This equalizes the amount of fuel in the siphon unit.

Disconnect the negative battery cable. See our tech article on battery replacing and reconnecting notes.

Remove the fuel cap. Then slide an anti-static siphon hose down the fuel filler neck. Once the hose has bottomed out, pump fuel out of the fuel tank into a suitable storage container. If you are unsure of the amount of fuel in your tank, you can monitor the fuel level via the fuel level sender units. As the fuel level drops, the fuel level sender resistance drops. You can measure this across the terminals at both sender units with a digital volt / ohm meter (DVOM). You will need a wiring diagram from a repair manual.

Read the Full Article:
https://www.pelicanparts.com/techarticles/Mercedes-W211/77-FUEL-Fuel_Pump_Replacement/77-FUEL-Fuel_Pump_Replacement.htm

Time: 3 hours
Tab: $300
Tools: Flathead screwdriver:https://www.pelicanparts.com/Mercedes-Benz/catalog/tools/screwdrivers.htm?utm_source=SuperTech_header&utm_medium=web&utm_campaign=tool_links&utm_content=screwdriver, 8mm socket:https://www.pelicanparts.com/Mercedes-Benz/catalog/tools/sockets-ratchets-drive.htm?utm_source=SuperTech_header&utm_medium=web&utm_campaign=tool_links&utm_content=socket, fuel pump collar tool:https://www.pelicanparts.com/Mercedes-Benz/catalog/tools/lubrication-equipment.htm?utm_source=SuperTech_header&utm_medium=web&utm_campaign=tool_links&utm_content=pump
Applicable Models: Mercedes-Benz W211 (2003-09):https://www.pelicanparts.com/catalog/SuperCat/W211_catalog.htm
Parts Required: Fuel pump, fuel pump sealing O-ring, fuel pump collar:https://www.pelicanparts.com/catalog/SuperCat/W211/MBZ_W211_FULFUL_pg3.htm#item7
Hot Tip: Clean top of fuel tank before removing pump
Performance Gain: Repair faulty fuel pump
Complementary Modification: Replace fuel filter:https://www.pelicanparts.com/techarticles/Mercedes-W211/78-FUEL-Fuel_Filter_Replacement/78-FUEL-Fuel_Filter_Replacement.htm

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