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Pelican Technical Article:

Fuel Pumps Removal

Kerry Jonsson

Time:

2 hours2 hrs

Tab:

$500

Talent:

**

Tools:

Phillips head screwdriver, 17mm (2) and 19mm wrenches

Applicable Models:

Mercedes-Benz R129 (1990-02)

Parts Required:

Fuel pumps (2), cooper washers

Hot Tip:

Run engine with fuel pump fuse removed to relieve the pressure in the fuel system

Performance Gain:

Proper engine function

Your engine needs three things to make it run, air, spark and fuel. In order for any fuel injected four stroke engine to run the fuel injectors must be supplied with fuel pressure. On our 500SL and SL500 Mercedes Benz uses two identical fuel pumps attached in series to provide adequate fuel pressure and fuel volume to the fuel injection system. These two external fuel pumps are mounted underneath the car, just in front of the differential on the right side. In this tech article we will go over all the steps to safely remove your fuel pumps for replacement.

In order to remove your fuel pumps you will need to raise and support at least the rear of your vehicle. See our technical article on jacking up and supporting your vehicle. You should also disconnect the battery; see our tech article on battery replacement.

This picture illustrates the fuel pump assembly under the rear of the car where the driveshaft meets the differential.
Figure 1

This picture illustrates the fuel pump assembly under the rear of the car where the driveshaft meets the differential. Begin by clamping off the feed line to the pump (or gas will run all over). Loosen the Phillips head hose clamp (green arrow). The clamp may be a different style if it has been previously replaced.

Slowly pull the hose off of the fuel pump.
Figure 2

Slowly pull the hose off of the fuel pump. Fuel is going to come out of this hose and the pump. Have a drain pan around to catch the fuel and let it drain for a few minutes. Do not have an ignition source of any kind (drop lamp) around and you should have a fire extinguisher around just in case. Work in a well-ventilated area and wear eye protection.

Remove the 17mm fitting that connects the output line of the fuel filter.
Figure 3

Remove the 17mm fitting that connects the output line of the fuel filter.

ThisPicture illustrates the left side fuel pump assembly that faces the driveshaft.
Figure 4

ThisPicture illustrates the left side fuel pump assembly that faces the driveshaft. Remove the two rubber hangars (green arrows) that suspend the fuel pump assembly below the body of the car.

ThisPicture illustrates the right side of the fuel pump assembly that faces the tire.
Figure 5

ThisPicture illustrates the right side of the fuel pump assembly that faces the tire. Remove the two rubber hangars (green arrows) that suspend the fuel pump assembly below the body of the car.

You can remove the hangars by hand.
Figure 6

You can remove the hangars by hand. It doesnÂ't matter if you leave the rubber hangars on the car or on the fuel pump assembly. We have chosen to remove the rubber hangars on the fuel pump assembly side.

While the assembly is hanging down remove the two 6mm fasteners (green arrows) and two 8mm fasteners (yellow arrows) that hold the power and ground supply to each of the two fuel pump motors.
Figure 7

While the assembly is hanging down remove the two 6mm fasteners (green arrows) and two 8mm fasteners (yellow arrows) that hold the power and ground supply to each of the two fuel pump motors. Then remove the wiring from the terminals on the fuel pump.

Loosen the hose clamp and remove the fuel return line hose from the pressure regulator that is part of the fuel pump assembly.
Figure 8

Loosen the hose clamp and remove the fuel return line hose from the pressure regulator that is part of the fuel pump assembly.

You can now remove the fuel pump assembly from the car and place it on a metal tray to catch any leaking gasoline and you can work on the assembly now.
Figure 9

You can now remove the fuel pump assembly from the car and place it on a metal tray to catch any leaking gasoline and you can work on the assembly now. Loosen the two fasteners (green arrows) that hold the bracket that clamps down on the fuel pumps.

Depending on time and age corrosion may hold these fasteners on very tight.
Figure 10

Depending on time and age corrosion may hold these fasteners on very tight. Here the middle fastener (green arrow) snapped off. We are going to have to drill out the other side of the bracket and use a new bolt and nut.

Remove the two 17mm fasteners (green arrows) that hold the fuel lines onto the fuel pump.
Figure 11

Remove the two 17mm fasteners (green arrows) that hold the fuel lines onto the fuel pump. Also, loosen the Phillips head clamp (yellow arrow) on the other side of one of the pump.

When loosening the upper fastener that holds the fuel line to the pump keep an eye out for two copper crush washers that help seal the fuel lines.
Figure 12

When loosening the upper fastener that holds the fuel line to the pump keep an eye out for two copper crush washers that help seal the fuel lines. YouÂ'll want to replace these with new.

Slide the upper pump in thePicture in the direction of the blue arrow.
Figure 13

Slide the upper pump in thePicture in the direction of the blue arrow. The threaded fitting will be pulled out of the line. This will allow you to pull the line off of the lower pump in thePicture. Slide both the fuel pump and the fuel line in the direction of the blue arrow until the rubber hose is off of the lower pump.

With the hose off of the lower pump move the fuel line out of the way on the upper pump and slide the upper pump in the direction of the blue arrow.
Figure 14

With the hose off of the lower pump move the fuel line out of the way on the upper pump and slide the upper pump in the direction of the blue arrow.

With the upper pump removed remove the black spacer that holds to two pumps in place within the bracket.
Figure 15

With the upper pump removed remove the black spacer that holds to two pumps in place within the bracket.

To remove the lower pump you need to remove the metal line that connects the lower fuel pump to the filter and the pressure regulator.
Figure 16

To remove the lower pump you need to remove the metal line that connects the lower fuel pump to the filter and the pressure regulator. Remove the 17mm banjo bolt (green arrow) on the filter and the 17mm fitting (yellow arrow) on the fuel pressure regulator. Move the line out of the way.

With the metal line out of the way slide the lower fuel pump out of the mounting bracket.
Figure 17

With the metal line out of the way slide the lower fuel pump out of the mounting bracket. Installation is the reverse of the removal procedures. Install the lower pump first and then the metal line that connects the fuel pump to the fuel filter and the fuel pressure regulator. Position the black plastic spacer and install the upper pump and connect the line with the rubber end to the lower pump and the metal banjo fitting on the upper pump. Install the banjo cap fasteners on both the upper and lower fuel pumps and tighten the hose clamp on the other side of the lower pump. Tighten the fasteners that clamp the bracket onto the fuel pumps. With the fuel pump assembly together position it under the car and attach the electrical wiring as you took it off. Lift the fuel pump assembly and attach the four rubber hangars that suspend the fuel pumps assembly under the body of the car. Install and tighten the large feed line from the fuel tank and the fuel output line on the filter. Turn on the ignition and crank the engine. Verify you do not have any fuel leaks before you take the car off of the jack stands. Once on the ground verify the car starts.

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Comments and Suggestions:
Bill Comments: You should tell them to block off the fuel line or they will be there a long time waiting for the gas to stop ;-
August 6, 2016
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
 
bbfers Comments: have 91 sl500 starts good idles for few mins then surges and stalls, will start up right away runs surges then stalls replaced fuel filter thinking now it's the pumps. noticed in 93 they change to 1 pump can i covert my car to 1 pump, how do i test them thks
July 27, 2016
  Followup from the Pelican Staff: Try this, found it on the web. - Nick at Pelican Parts
Bob Comments: Finally some understandable help. Thank you !!
Do you have anything on how to read pin codes? Check engine light on but car runs good.
June 5, 2016
  Followup from the Pelican Staff: Yes, you will need a scan tool. Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts  
Charles Comments: '94 SL320, I couldn't get the support screws back in and after 20 minutes of frustration and broken plastic, I said, "screw it," and got some zip-ties and fed them through the screw holes. worked great, holds great, and was done in 60 seconds!
June 1, 2016
  Followup from the Pelican Staff: Not a good idea. The plastic straps will fail. I would work to align it all correctly, you may have to loosen some connections, then install the fasteners. - Nick at Pelican Parts  
Cas Comments: My 1994 S500 Coupe will not start execpt when I prime the engine. I am not getting any electrical current to the fuel pump. Is there a enertia switch or wath could it be. I have current to the fuel pump relay and fuse. from the relay to the pump dead.
May 25, 2016
  Followup from the Pelican Staff: no inertia switch, just a relay. the relay is either not being activated or is faulty. - Nick at Pelican Parts  
Andymac Comments: What should the working fuel pressure be on the fuel rail? all I find are examples of incorrect pressures. Also what is the part number for pressure regulator at pump assembly? 1993 500SL 100k
May 16, 2016
  Followup from the Pelican Staff: This is all I have:


Fuel Pressure, psi 54-61 - Nick at Pelican Parts
 
Rod Comments: 94 SL500. Runs great until it gets warmed up. Then it got really rough and wouldn't idle. Just turned over 100k miles. Replaced distributors and plugs. Now it's not rough but when it gets heated up, on the highway at 60 MPH, 2k rpm, nothing happens when you step on the gas. Fuel consumption pegs high 30mpg with the accelerator floored but no response in power. Downshift to 3rd, stays at 60MPH, but rpm goes to 3k. I was going to start replacing fuel system parts, but thought I'd check in first.
April 24, 2016
  Followup from the Pelican Staff: Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders.
- Nick at Pelican Parts
 
Ivan s Comments: I have a 1993 600 sl, it runs good but after 20/30 minutes it cuts of no fuel but when it cools down it starts fight up
March 9, 2016
  Followup from the Pelican Staff: Sounds like a sensor issue to me. I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
Mel Comments: I have a SL500. It would act like it was missing when starting. Tried to start several times and would finally start and run. Eventually the car wouldn't start. I replaced the fuel filter and it will start but has no power when you put it in gear and feels like it is out of time even though it has 1200 rpm.
November 18, 2015
  Followup from the Pelican Staff: Sounds like an engine misfire. I would check spark, fuel and compression on all cylinders.
- Nick at Pelican Parts
 
txnese Comments: I have a 1995 SL600 that had a dead battery. Put a new battery in and it doesn't start. I don't hear the fuel. Tested for voltage at the pump, but don't seem to have any. Thought about jumping 12v directly to it, but not sure how to do it and don't want to damage anything. I can hear the fuel relay clicking. Is there anything between the relay and pump that would keep it from getting power?
November 4, 2015
  Followup from the Pelican Staff: No, power is supplied directly from the relay. You can used fused jumper wires to power it. - Nick at Pelican Parts  
sl320 Comments: Hello, I have a 96 sl 320. I think my fuel pump is going out. Does the sl 320 has two or one fuel pump. Thank you.
May 25, 2015
  Followup from the Pelican Staff: I recall there being only one.

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Parm Comments: This is an excellent write up that I just stumbled upon while looking up other information. I was looking for this back in June '14 and was unable to find any information on where these were even located let alone the step-by-step. Thank you. Now only if the 17mm fitting that connects the output line of the fuel filter was not completely rusted solid I would have been ahead of the game. Nothing can be easy.
April 30, 2015
  Followup from the Pelican Staff: Try flat-jaw visegrips on the rusted lines. - Nick at Pelican Parts  
Cpttrevor Comments: Thank you for your response. I have solved the problem one of the pumps are bad
January 3, 2015
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
cpttrevor Comments: my 1991 500sl starts and shut down in seconds I have fuel in distributor but it is not going into injectors. I have w129 series. Does this car carries two fuel pumps?. A primary and a secondary? Please advise.
January 1, 2015
  Followup from the Pelican Staff: What is fuel pressure and volume? - Nick at Pelican Parts  
sl6 Comments: R129
September 16, 2014
  Followup from the Pelican Staff: Can't be sure. We don't have those in the US. - Nick at Pelican Parts  
Sl6 Comments: This is the return fuel filter and pump, correct? What about the ones in the tank?
September 3, 2014
  Followup from the Pelican Staff: I don't believe W129 has a pump in the tank. These are it. - Nick at Pelican Parts  

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