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Pelican Technical Article:

Replacing Your Fuel Pumps

Steve Vernon

Time:

2 hour2 hr

Tab:

$100 to $240

Talent:

**

Tools:

10mm socket, 7mm, 8mm, 17mm (2) wrenches, Phillips-head screwdriver

Applicable Models:

Mercedes-Benz W124 (1986-95)

Parts Required:

Fuel pumps (2), rubber hangers

Hot Tip:

Plan on replacing the hangers while you are in there

Performance Gain:

Proper fuel pressure

Complementary Modification:

Replace your hangers and check your lines

Your fuel pumps are an integral part of the fuel delivery system. A clogged or faulty pump can cause all kinds of problems, from a rough running engine to leaving you stranded on the side of the road. It is a good idea to change your pumps at the first signs of it going bad (trouble starting).

The W124 fuel pumps are located on the underside of the car; one pump is located behind the rear right side seat, the other is behind the rear cross-member to the right of the differential.

You will need to safely lift and support your car. Please see our article on jacking up your Mercedes-Benz. You will be working around gasoline so make sure to use eye and skin protection. There will be some spillage no matter what precautions you take so be prepared to catch any spills and dispose of the waste according to the regulations in your area.

You are going to be working around the electrical connections for the pumps so begin by locating the ground post (yellow arrow) on your battery and disconnecting the cable (red arrow).
Figure 1

You are going to be working around the electrical connections for the pumps so begin by locating the ground post (yellow arrow) on your battery and disconnecting the cable (red arrow). Make sure the cable cannot accidentally come in contact with the terminal while you are working.

The rear pump draws gasoline directly from the tank and is located under a plastic cover mounted just behind the rear cross-member (red arrow).
Figure 2

The rear pump draws gasoline directly from the tank and is located under a plastic cover mounted just behind the rear cross-member (red arrow).

Unclip the plastic cover from the rubber hangers and remove it.
Figure 3

Unclip the plastic cover from the rubber hangers and remove it. With the cover removed you can see the line from the tank into the pump (red arrow) and the banjo fitting for the line out (yellow arrow).

Use an 8mm wrench and remove the ground connection (red arrow) and then a 7mm wrench for the power side (yellow arrow).
Figure 4

Use an 8mm wrench and remove the ground connection (red arrow) and then a 7mm wrench for the power side (yellow arrow).

Place a large hose clamping tool on the input line (red arrow) to stop the flow of gas.
Figure 5

Place a large hose clamping tool on the input line (red arrow) to stop the flow of gas. If you do not have the proper tool you can try wrapping vice grips in a rag to pinch the line. Do NOT put the metal teeth against the rubber line. This is also a good time to check your lines for any aging, cracks, bulges or dry rot and replace as needed. With the hose pinched off remove the Philips heads screw from the hose clamp and wiggle the line off the pump (yellow arrow). Be prepared for any gas remaining in the line of the pump to spill out.

Use a 17mm wrench to hold the pump and another 17mm wrench to remove the bolt (red arrow) through the banjo fitting (yellow arrow).
Figure 6

Use a 17mm wrench to hold the pump and another 17mm wrench to remove the bolt (red arrow) through the banjo fitting (yellow arrow). Remove the fittings from the pump. Note: always replace the brass washers between the fittings on the lines.

There are two rubber hangers that hold the pump.
Figure 7

There are two rubber hangers that hold the pump. Lift the pump up off the hangers (yellow arrow) and remove the rubber from the pump (red arrow). Inspect the condition of the rubber hangers and replace them as needed. Installation is the reverse of removal.

There is a second pump mounted under a protective plate in the right side of the under carriage.
Figure 8

There is a second pump mounted under a protective plate in the right side of the under carriage. Remove the four 10mm plastic screws (red arrows) and pull the cover down and out. Use care as all kinds of things can collect under the cover.

With the cover removed you can see the pump (red arrow) and the fuel filter (yellow arrow).
Figure 9

With the cover removed you can see the pump (red arrow) and the fuel filter (yellow arrow).

Replacement of this pump is the same procedures and the rear pump with the following exceptions.
Figure 10

Replacement of this pump is the same procedures and the rear pump with the following exceptions. The input line becomes a hard line and wraps around the pump to join it at the rear. Pinch off the soft rubber line before the hard line connection (red arrow) and then remove the Philips heads screw. Clamp and slide the rubber fitting off the pump (green arrow). The pump is held in place by two Philips head screws (yellow arrow). Remove the screws and lower the pump down. The new pump may come with a rubber sleeve, if it does not transfer the sleeve on the old pump to the new one. Installation is the reverse of removal. With everything in place, turn on the ignition and check for leaks. Turn off the ignition, reinstall the cover plates and you are good to go.

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Page last updated: Fri 6/23/2017 02:42:07 AM