Announcement

Collapse
No announcement yet.

S50B32 Z3M Coupe / Roadster Lambda/Oxygen Sensor Replacement

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • S50B32 Z3M Coupe / Roadster Lambda/Oxygen Sensor Replacement

    Having recently failed the MOT on the lambda reading, and not being able to find a how to guide to replace the two lambdas, I thought I'd do a quick write up.

    The lambda reading on modern cars basically shows whether the fuel:air mix is optimal (known as the stoichiometric value). When lambda=1, the fuel to air mix is optimal.

    The lambda / oxygen sensors in our cars are used to adjust fuelling on the fly. If the lambda sensors in the exhaust (pre-cat) senses that there is too much oxygen remaining after combustion, it will increase fuelling; too little and it will reduce fuelling.

    In the MOT, cars are allowed a variance of 3% i.e. lambda value of 0.97 or 1.03. A value of less than one indicates that there is fuel which has not been burned existing in the exhaust. A value of more than 1 indicates that there is too much oxygen in the exhaust (hence known as an oxygen sensor!)

    Should your M fail the MOT, however, don't simply assume that the lambda sensors are in need of replacement. The reason is that the MOT lambda reading is taken at the end of the exhaust, and therefore the following steps should be taken first.

    1) Ensure there is no leak in the exhaust. An exhaust leak after the lambda sensor could draw in air from the outside, hence there will be excess oxygen.

    2) Check vacuum hoses around the engine block.

    3) Read your codes!

    Right then, onto the tutorial!

    Tools needed:

    Philips Screwdriver
    10mm socket
    8mm socket
    Lambda sensor removal tool: LINK
    2x Lambda Sensors (different length cables):
    Part number 11781406621
    Part number 11781406622
    Lump hammer
    Penetrating Spray
    Four post lift / pit in your garage. I wouldn’t attempt this by jacking up the car and crawling underneath, as access is extremely limited

    Step 1 – Remove the undertray

    There are 2x10mm bolts at the front, 6x8mm bolts around the other three sides and 1x screw in the middle. Below is a picture of the undertray


    You will now be able to see the lambda sensors, toward the front of the visible exhaust



    Step 2 – Use the penetrating spray!

    The lambda sensors have been expanding and contracting for many cycles, so they will be pretty tough to get out. Spray liberally!

    Step 3 – Undo the first lambda sensor

    Slip the tool over the first lambda sensor (to the left hand side of the car). Turn anti-clockwise (towards the back of the car). At this point it may still be stuck, so I used a lump hammer to “persuade” it. That loosened it! You can probably turn the rest of the way by hand once freed.

    The wiring is routed along the heat shield towards the back of the car, across and then back towards the heat shield on the other side of the car. The connectors are shown here:



    Step 4 – remove the other lambda!

    Again, use the tool and a lump hammer. Make sure you remove this sensor before replacing the other, as you’ll have no chance otherwise.

    Step 5 – replacement is the reverse of removal.

    Just remember to plug the lambda’s into the right connector

    Build thread: https://www.z3mcoupe.com/forum/showthread.php?t=19347

  • #2
    Quick tip I used last time I had to do this job was to warm the exhaust up by running the engine.

    Not too hot obviously, but just enough to allow metal expansion. If the old ones are really stubborn then it's worth a try.

    Good write up :-)

    Comment


    • #3
      Interesting write up. Local Indy has just quoted me £466 to replace both the pre cat O2 sensors on my s54.

      Comment


      • #4
        Just got quoted £250 plus vat to replace a pulley from a prior decent garage. £11part delivered and 20mins spanner done.

        Comment


        • #5
          Originally posted by Bi11 View Post
          Interesting write up. Local Indy has just quoted me £466 to replace both the pre cat O2 sensors on my s54.
          If you have access to a pit or 4 post lift it's dead easy

          Build thread: https://www.z3mcoupe.com/forum/showthread.php?t=19347

          Comment


          • #6
            After reading your write up I am tempted to have a go, but I am usually a mechanical disaster area and end up shearing or stripping something! Found another Indy who sounded a lot more enthusiastic, knowledgable and reasonable priced.

            Comment


            • #7
              It's pretty easy, and the lambdas cost £150 in total

              Build thread: https://www.z3mcoupe.com/forum/showthread.php?t=19347

              Comment


              • #8
                May I ask where you got your sensors from? Bmw quoted me £150 EACH

                Comment


                • #9
                  I *think* I hot them off eBay

                  Build thread: https://www.z3mcoupe.com/forum/showthread.php?t=19347

                  Comment

                  Working...
                  X