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DIY - Walbro 255 fuel pump retrofit.

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    DIY - Walbro 255 fuel pump retrofit.


    I looked all over for a Walbro writeup or any information regarding this modification. Considering how easy this was and how little information was available. I decided it was about time for me to contribute to r3v. This was done on my 89 325i, and can be done word for word for any car with only an in tank pump. Entire mod start to finish took a half hour while taking pictures.

    The earlier models have a transfer pump and an in tank pump and I don't know exactly how this would work without removing the other pump. So DO NOT expect this to work as said in this writeup exactly as written.

    Pictures are located at bottom of post.


    To start this off, here are the parts you will need.

    1. Walbro 255 fuel pump
    Fuel Pump Model # GSS-340
    Pump kit model # 400-812
    This is the 'kit' for a 85-97 Ford Mustang
    2. 1'' to 2'' stainless hose clamps, small screw
    3. Fuel filter. A good 'while your at it' thing because the system isn't pressurized.


    1. Phillips screwdriver
    2. Flathead screwdriver
    3. 8mm socket
    4. Small hammer
    5. Pliers
    6. Soldering iron(optional)


    1. Start by disconnecting the battery.
    2. Take out the bottom cushion of the rear seat. there are tabs under each butt pad. Push them towards the trunk of the car and pull up to remove cushion.
    3. (Image 1) On the passenger side of the panel under the seat. there is a black cover for the fuel pump. Use the Phillips screwdriver to remove this cover.
    4. (Image 2) Loosen the hose clamp exiting the top of the fuel pump. Unplug electrical plugs.
    5. (Image 3) Remove the four 8mm nuts holding in the fuel lever sender, and pull straight up to remove sender.
    6. Use the Flathead screwdriver and the hammer to break loose the fuel pump assembly from the tank. Counter-clockwise, one hit should get it loose enough to remove straight up by hand.
    7. Adult beverage time, you've done the hard part. Yes really.


    (Image 4) As you can see these pumps are close in size, you could technically unplug the original pump into the brown coupler and secure the Walbro to the rod but the pickup would be about an inch higher than the original pump was, resulting in less usable fuel. (Image 5) The fuel pump kit comes with almost everything you need for the retrofit. Extra parts are minimal. I used old BMW clamps as the screw mechanism was thinner than the ones i bought at Lowe's. The Lowe's ones were too thick and wouldn't allow the pump to fit trough the fuel tank hole.

    1. Remove old fuel pump from rail. Basically pull it off.
    2. Remove the bottom metal shelf that the old pump rested on. Use the pliers to break it off the rod that goes down.
    3. Use pliers to bend a small tab for the new pump to rest on, maybe 5mm at most.
    4. (Image 6) Install new fuel pump and strap to the rod using the two stainless hose clamps.
    5. Cut supplied hose to fit between the new pump and hose. Secure with supplied hose clamps.
    6. Use either Supplied butt connectors or solder new pump wires to bottom of the two prong connector. (On my car, looking at the plug, the prong on the left was ground. On the right was power. Please use multimeter to confirm this on your car.)
    7. Reinstall opposite of removal.
    8. Probably a good time to replace your fuel filter while your at it.


    My car has had this fuel pump with no other modifications for about a week now. I haven't notices any ill effects. In fact, my random long starting problem has disappeared. I suspected that brown connector on the old pump was letting pressure leak out of the lines when car was not running. Also this pump makes less noise than my old pump, but my old pump sounded like a supercharger on its way out. I can barley hear the pump from outside the car, but not from inside the car.

    Questions, comments, always appreciated. Complaints, go buy a stock pump.


    Image 1

    Image 2

    Image 3

    Image 4

    Image 5

    Image 6


    awesome now DIY on solving fuel starvation??

    : /

    i may eventually leave my walbro like you have it. and add a surge tank like thisone:

    explanation here:

    but with the second pump inside of this tank for cooling.

    here's another dual pump setup that claims to have worked well.
    No more e30s for me.
    88 black BMW OBDII 332is dedicated track [sold]
    88 BMW OBDII bronzit 332is [RIP 03/08]
    91 BMW 325i [sold]
    86 Corolla 'Ae86' HB 20v trd [sold]


      Patrick P. seems to have the ideal fueling setup from what I've seen. He's using the Porsche 911 Turbo pump along with a Walbro as well.

      600rwhp+ and never misses a beat.
      Erick Mahle | FullOpp Drift | YouTube
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      Originally posted by Mr. Anderson of the most hardcore E30's around. :D


        Originally posted by Erick View Post
        Patrick P. seems to have the ideal fueling setup from what I've seen. He's using the Porsche 911 Turbo pump along with a Walbro as well.

        600rwhp+ and never misses a beat.
        how did he set it up?
        '15 Porsche GT3 - 7-speed PDK - Daily Driver
        '86 325es - s54b32tu - 6-speed - Mtech 1
        '89 325is - m20b25 - 5-speed - Individual


          yeah who is Patrick P.?
          No more e30s for me.
          88 black BMW OBDII 332is dedicated track [sold]
          88 BMW OBDII bronzit 332is [RIP 03/08]
          91 BMW 325i [sold]
          86 Corolla 'Ae86' HB 20v trd [sold]




              ^ +1

              also curious about the dual pump setup?

              My LS1 swap thread:


                whats there to be curious about? im digging the surge tank idea though. But thinking it through i wouldnt really like the battery and the surge tank to be mounted in the boot which would mean mounting it in the cabin which isnt really a great idea.


                  Bringing this back from the dead... In theory... couldn't one "delete" the dual pump setup and just run the Walbro unit on the early model cars?

                  I am curious if anyone has tried this.


                    in theory i believe you can but im not completly sure as long as you got the flow rates right


                      I'm thinking about this soon for my 86es. I bought a tre pump for in the tank....but I cant decide if I just want the tre to be a lift pump the second factory pump.... Or if I want it to just feed the entire system.

                      After some reading I have been doing the last couple days, some people claim the two pump setup is better and in theory I can understand how...... so I'm up in the air about it.

                      BUT THIS!!!!!


                        The two pump system with the addition of a small aux gas "tank" can eliminate any/all fuel starvation issues vs. running 1 pump.

                        Also, keep in mind how/where the fuel return line goes on the cars with 1 pump vs 2 pump goes to the intank pump, and one goes to the gas tank..
                        Mtech1 v8 build thread -

                        OEM v8 manual chip or dme -


                          I know when I get down below say around 1/4 tank...under hard acceleration I experience some starvation issues in the form of mild hesitation. I noticed above that fuel level mark the car runs fine.

                          BUT THIS!!!!!


                            Thanks for this. Just got done with this mod and the car runs great.


                              nice DIY! thanks
                              Driving:1990 325iS, 2007 335i :devil:
                              past BMWs: 1987 325iS turbo, 1989 325i, 1995 525i, 2000 328CI, 2001 540i, 2008 135i