Mercedes-Benz Parts Catalog Mercedes-Benz Accessories Catalog Mercedes-Benz Technical Articles Mercedes-Benz Tech Forums
 
Follow Pelican Parts on Facebook Follow Pelican Parts on Twitter Follow Pelican Parts on Instagram Follow Pelican Parts on YouTube Follow Pelican Parts on Pinterest Follow Pelican Parts on Tumblr
  Search our site:    
View Recent Cars  |   Cart  | Project List | Order Status | Help    
Bookmark and Share

Pelican Technical Article:

Replacing the Fuel Pump

Mike Holloway

Time:

1 hour1 hr

Tab:

$100 to $200

Talent:

*

Tools:

8mm, 10mm, and 13mm socket wrench with 6-inch extension, 8mm, and 17mm open end wrench, flat face and Phillips head screwdriver, floor jack and jack stands

Applicable Models:

Mercedes-Benz 450SL (1975-80)

Parts Required:

Fuel pump

Hot Tip:

Clamp fuel line

Performance Gain:

Engine operation

Complementary Modification:

Replace fuel filter

The fuel pump's job is to supply the engine more than enough fuel in order to maintain pressure. Circulating excess fuel keeps fluid temperatures lower and inhibits bubbles: the dreaded vapor lock. The pump pushes fuel from the tank through the fuel filter and lines/rail to the injectors. Fuel system problems can result from many variables. If the car has spark but won't start, then the culprit is more than likely a fuel problem. Rough idle, stumbling and stalling on hills are other symptoms of fuel-delivery issues.

When troubleshooting the fuel pump, first you should check that the fuse isn't blown and its relay and other fuel-system components pass their tests.

Fuel pumps often give a whirring sound as they approach the end of their service life. Another telltale sign of fuel pump issues would be lack of fuel or insufficient fuel at the rail's Schrader valve when cranking the engine. Make sure to have rags and a fire extinguisher handy in case fuel does squirt out. Also, if the pump is getting power (verified with a multi-meter) but no fuel is arriving at the engine, the pump could be bad. Corroded terminals can also cause fuel pump malfunction.

Potential for fire is always a concern when working on fuel systems. Disconnect the battery's negative cable to minimize possibilities of sparks. Work in a well-ventilated area away from open flame. Let the car cool down before beginning. Fully heated catalytic converters can ignite fuel vapors.

Always keep a Class B fire extinguisher within arm's reach. Capture gas in an appropriate container. Relieve pressure from the fuel system before removing the existing fuel pump. Pinching off the suction hose will minimize the amount of spilled gas. Special U-style clamps are made for this purpose, although DIY mechanics often improvise with small C-clamps or locking pliers using something to protect the fuel line from the pliers' jaws. The OEM sliding-style hose clamps are realistically one-use only. Spring-type clamps are DIY-friendly and are normally packaged with the new fuel pump. In a pinch, worm-gear clamps have decades of proven effectiveness, providing they aren't over or under tightened. Many fuel pump kits include new clamps.

Once lines are disconnected, access is eased by sliding the pump out of the bracket. The bracket's hangers can also be unhooked from their rubber mounts to lower the pump. On reassembly, make sure that the new fuel pump's protective sleeve is centered in the mounting bracket's clamp. Otherwise, corrosion can form between the clamp and the pump's body. Since 1980 the fuel pump is provided with a special coating on a roller running surface, an exchangeable check valve, and a plastic sleeve to prevent contact corrosion.

Disconnect the negative terminal on the battery prior to any work. Make sure the work area is well ventilated. The fuel pump is located under the car on the right side below the fuel-filling inlet near the fuel tank.

Consult the article on safely jacking up your vehicle and placing your M-B on jack stands. Be sure to always wear safety glasses anytime you're working under your car. You don't want the rust and dirt particles from your car's undercarriage getting in your eyes.

The fuel pump is located behind the rear trans axle and below the fuel tank.
Using a 13mm socket, loosen and remove the (2) bolts that hold the plastic protective shield.
Figure 1

Using a 13mm socket, loosen and remove the (2) bolts that hold the plastic protective shield.

Using a 8mm socket, loosen and remove the two nuts that secure the clamp for the fuel pump.
Figure 2

Using a 8mm socket, loosen and remove the two nuts that secure the clamp for the fuel pump.

Using a flat face screwdriver, loosen the clamp, which feeds the fuel pump.
Figure 3

Using a flat face screwdriver, loosen the clamp, which feeds the fuel pump. If the fuel line is not clamped, place a proper receptacle to catch any fuel which is in the lines.

Using an 8mm open-end wrench, loosen and remove the two nuts that secure the electrical terminals on the fuel pump.
Figure 4

Using an 8mm open-end wrench, loosen and remove the two nuts that secure the electrical terminals on the fuel pump.

Using a 10mm socket, loosen and remove the nut towards the rear, which secures the fuel delivery system.
Figure 5

Using a 10mm socket, loosen and remove the nut towards the rear, which secures the fuel delivery system.

Using a 10mm socket, loosen and remove the nut towards the front, which secures the fuel delivery system.
Figure 6

Using a 10mm socket, loosen and remove the nut towards the front, which secures the fuel delivery system.

Using a 17mm open-end wrench, loosen and remove the fuel line from the rear of the fuel pump.
Figure 7

Using a 17mm open-end wrench, loosen and remove the fuel line from the rear of the fuel pump. Make sure that a proper fuel receptacle is in place to catch any fuel that may leak from the pump.

Using a flat face screwdriver loosen the hose clamp which secures the fuel suction dampener.
Figure 8

Using a flat face screwdriver loosen the hose clamp which secures the fuel suction dampener. Make sure that a proper fuel receptacle is in place to catch any fuel that may leak from the fuel suction dampener.

The fuel delivery system can now be removed.
Figure 9

The fuel delivery system can now be removed. Using a 17mm open-end wrench loosen and remove the fuel line, which feeds the fuel pump.

The fuel pump is now free to replace.
Figure 10

The fuel pump is now free to replace.

Replacement is the reverse of removal.
Figure 11

Replacement is the reverse of removal.

Bookmark and Share
Comments and Suggestions:
Jerry Comments: You tell everything EXCEPT WHERE the fuel pumps are located to start the job!!
May 7, 2016
  Followup from the Pelican Staff: They are mounted under the rear of the vehicle. I will have a location photo added to the article. Thanks for the feedback, we appreciate it. - Nick at Pelican Parts  
Jennafine Comments: 1974 450 sl came with no fuel pump . Installed an oem pump and the terminals look to be the same size so which wire goes to which terminal?? They are Green an Brown. Any help would be great Thank you , Jenna
January 13, 2016
  Followup from the Pelican Staff: Brown is the ground, put it on the terminal with the (-) symbol. - Nick at Pelican Parts  
Hugo Comments: Is a washer needed under fuel pump cap? I put one in and it's leaking at that point.
June 8, 2015
  Followup from the Pelican Staff: The banjo bolts have a washer on each side of the line. Is that what you needed to know? - Nick at Pelican Parts  
bfgamer Comments: Looking at figure 4. Does the short contact wire go to the negative terminal? There is a shadow and I cant tell.
April 21, 2015
  Followup from the Pelican Staff: The terminal ends on the wires are two different sizes. Match them up to the stud of the correct size. - Nick at Pelican Parts  

  Search our site:    

View Cart & CheckOut | Project List | Order Status |  Help    

 

[Home] [Customer Service] [Shopping Cart] [Project/Wish List]
  [Privacy Statement]  [Contact Us] [About Us] [Shipping] [Careers]

Copyright © Pelican Parts Inc. -    DMCA Registered Agent Contact Page

Page last updated: Mon 12/5/2016 02:39:43 AM