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Fuel Pressure Regulator Replacement
 
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Pelican Technical Article:

Fuel Pressure Regulator Replacement

Steve Vernon

Time:

1 hour1 hr

Tab:

$60

Talent:

*

Tools:

Circlip tool, flathead screwdriver

Applicable Models:

Mercedes-Benz W124 (1986-95)

Parts Required:

New fuel pressure regulator

Hot Tip:

Work on a cold engine in a well-ventilated area

Performance Gain:

Proper running motor

Complementary Modification:

Change air filter

If your car is stumbling under acceleration it may be something as simple as a fuel pressure regulator going bad. You will want to eliminate a few common problems before you move to the fuel pressure regulator. Did you get some bad gas? How old is the fuel filter? Is your fuel pump operating correctly? These are some of the questions you should be getting answers to. One of the checks for the regulator is to remove the vacuum line. If you pull off the vacuum connection and there is fuel coming from the nipple, the regulator is bad and must be replaced.

You're going to be working on the fuel system so be prepared. Work in a well-ventilated area. Keep a fire extinguisher near you at all times and know how to use it correctly. No sparks or an open flame around. If you smoke now would be a really good time to quit, at least for the half hour it might take you to perform this job.

Just as with the fuel filter, injectors, or any other component of the fuel system, it's best to relieve the fuel system of any pressure before you go opening it up. The engine should be cold while doing this. Open the gas cap while the motor is cooling down and help relieve the vacuum in the system. Also, be sure to use some protective gloves and goggles whenever you're working with fuel.

Before you open the fuel system up it is a good idea to relieve the pressure in the system.
Figure 1

Before you open the fuel system up it is a good idea to relieve the pressure in the system. The best way to do this is to remove the fuel pump relay and crank the engine over a few times. This will draw the fuel already in the system out and relieve some of the pressure. The fuel pump relay is located in the upper right side of the engine bay behind the battery. There is a plastic tray behind the battery that you can move out of the way (red arrow).

If your hands are small enough you can reach down in the area between the hood and cowl and remove the fuel pump relay (red arrow).
Figure 2

If your hands are small enough you can reach down in the area between the hood and cowl and remove the fuel pump relay (red arrow). The relay sits tightly in the mount so wiggling it out helps. If your hands are too big you will need to remove the battery first to get at it from the front. Of course this means you will need to disconnect the battery to remove it then reconnect it to crank the motor with the relay removed. Please see our article on battery removal for further assistance.

Next remove the plastic cover (red arrow) protecting the wiring and fuel rail; it pulls straight up and off.
Figure 3

Next remove the plastic cover (red arrow) protecting the wiring and fuel rail; it pulls straight up and off. You will be working with the Schrader valve (green arrow) and the fuel pressure regulator (yellow arrow).

Open the cap on the Schrader valve (red arrow).
Figure 4

Open the cap on the Schrader valve (red arrow). Use a small flathead screwdriver and gently press the release valve. It is a good idea to have a rag wrapped around the valve to catch any fuel that will escape.

With the pressure relieved from the rail pull the vacuum line off the nipple on the valve (red arrow).
Figure 5

With the pressure relieved from the rail pull the vacuum line off the nipple on the valve (red arrow). The top of the valve can get very dirty (yellow arrow). Make sure to give it a good cleaning to prevent any dirt or debris from getting into the fuel system when you remove the valve.

Use a set of circlip pliers and remove the circlip from the valve (red arrow).
Figure 6

Use a set of circlip pliers and remove the circlip from the valve (red arrow). Another name for circlip is snap ring. In addition, circlip pliers are also referred to as snap ring pliers.

The circlip (red arrow) sits in a ring in the housing on the fuel rail.
Figure 7

The circlip (red arrow) sits in a ring in the housing on the fuel rail. The valve sits inside this housing (yellow arrow). Pull the valve straight up and out.

There are two O-rings on the valve (red arrow).
Figure 8

There are two O-rings on the valve (red arrow). There is no way to check the valves condition without a set of expensive fuel pressure gauges. Install the new regulator by putting a little clean gas on the O-rings and pressing the valve down into the housing with hand pressure. Installation is the reverse of removal.

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Comments and Suggestions:
jojo Comments: what causes the engine lost power when accelerating? thanks for answering my queries...
November 14, 2016
  Followup from the Pelican Staff: Could be an issue with the fuel pump. I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 
jojo Comments: from where the vacuum hose connected before it was installed on the fuel pressure regulator?
November 10, 2016
  Followup from the Pelican Staff: The vacuum hose connects to the rear of the intake manifold. - Nick at Pelican Parts  
Puggy Comments: Car will not start/run. I just finished replacing old fuel filter, replaced and put in new fuel pumps 2, Also, I checked the pump fuel relay located behind the battery green cube with 30 amp fuse and the fuse is ok, not broken or cracked. I also did checked the fuel pressure regulator by testing it by removing the rubber hose connected to the fuel pressure regulator valve and start the engine to turn over and see if the fuel pressure regulator valve is shooting fuel and it did not, which means I supposed the fuel pressure regulator is working fine. The car still does not start/run. Any ideas, comments, feedback anyone?
February 29, 2016
  Followup from the Pelican Staff: Check if the filter is in backward. - Nick at Pelican Parts  
shng Comments: First of all, Thanks for the great article with detailed DIY instructions. I'm wondering if step 1 "Fuel pump relay removal" and cranking the engine to relieve the fuel system pressure can be bypassed? Since before removing the fuel pressure regulator, the fuel in the pipe needs to be released by the Schrader valve anyway. Perhaps without cranking the engine with Fuel pump relay removed, it may take longer to release remaining fuel in the pipe, but it would save the touble of removing the Fuel pump relay.

April 2, 2015
  Followup from the Pelican Staff: At times, I have used the just the Schrader valve to relieve fuel pressure, leaving the relay in place. However, removing the relay removes pressure from the fuel rail as well ensures no additional pressure will be introduced to the system. - Nick at Pelican Parts  

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