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  • Lambda reading

    Passed MOT this morning, all good, no advisories.

    However, Lambda reading was 1.03 (limit is 1.03!).

    CO reading was 0.01 (limit 0.2) therefore very low - a good thing.

    HC reading was 6 (limit 200ppm) so again very good.

    All readings same as last year (except HC which was 8 so this has improved).

    To the point, could any one explain what the Lambda reading measures/indicates? Also guessing it is measured by the pre cat sensors but don't know?

    Just about understand CO and HC, but Lambda?

    If I'm being dim I apologise in advance!
    S54 Titan Silver metallic. Black leather, most factory options including sunroof, Becker Cascade and Becker Silverstone changer.

  • #2
    A Lambda of 1.000 indicates that the fuel/air mixture is perfect, this is called the stoichiometric ratio.

    Your lambda sensors attempt to tell your ECU what to do to achieve this, the fact that the MOT tester's equipment gives a reading of 1.03 indicates that there is a calibration difference between your sensors and those of the test station (which should be more accurate).
    2000 Cosmos Black S50, Kyalami/Black interior, KW V3s, H&R ARBs, Supersprint exhausts, Apex ARC8s.
    1996 Dark Aubergine Escort Cosworth Lux with leather, GGR 305 chipped, GGR/Koni suspension, Black Diamond discs.
    2008 Orange/Black Westfield Megabusa, FW rear, Widetrack/Nitron Suspension, AP/Westfield 4 pots.
    Lots of Land Rovers!
    No wife or kids!!

    Comment


    • #3
      Thanks Limbs - assuming the MOT stations sensors are accurate (reasonable assumption), this would imply that my sensors are perhaps in need of replacement - would you agree?
      S54 Titan Silver metallic. Black leather, most factory options including sunroof, Becker Cascade and Becker Silverstone changer.

      Comment


      • #4
        The station's system will have to be calibrated frequently, so it's a reasonable assumption, but not a certainty! Could indicate a slight issue with your system somewhere, but I wouldn't tend to worry about it too much, it is within acceptable limits after all!

        Could try giving the sensors a clean!: http://www.driftworks.com/forum/tech...ng-advice.html
        2000 Cosmos Black S50, Kyalami/Black interior, KW V3s, H&R ARBs, Supersprint exhausts, Apex ARC8s.
        1996 Dark Aubergine Escort Cosworth Lux with leather, GGR 305 chipped, GGR/Koni suspension, Black Diamond discs.
        2008 Orange/Black Westfield Megabusa, FW rear, Widetrack/Nitron Suspension, AP/Westfield 4 pots.
        Lots of Land Rovers!
        No wife or kids!!

        Comment


        • #5
          Limbs,

          I bow to your expertise on this subject. Since the readings for CO and hydrocarbon are very low, then surely, the burn of fuel in Ian's car is virtually complete? If so, how could the lambda on Ian's car be wrong, whether or not the engine is being fuelled at stoichometric levels during the test? Just asking out of curiosity.
          /// Exdos ///
          "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

          Comment


          • #6
            I Don't have too much experience TBH, but a lambda reading of 1.03 only indicates a divergence of 3% from stoichiometry, therefore, I would imagine, the burn is still complete!
            2000 Cosmos Black S50, Kyalami/Black interior, KW V3s, H&R ARBs, Supersprint exhausts, Apex ARC8s.
            1996 Dark Aubergine Escort Cosworth Lux with leather, GGR 305 chipped, GGR/Koni suspension, Black Diamond discs.
            2008 Orange/Black Westfield Megabusa, FW rear, Widetrack/Nitron Suspension, AP/Westfield 4 pots.
            Lots of Land Rovers!
            No wife or kids!!

            Comment


            • #7
              Is any of the above available in English ?

              Comment


              • #8
                Yes, but not for thickos!!
                2000 Cosmos Black S50, Kyalami/Black interior, KW V3s, H&R ARBs, Supersprint exhausts, Apex ARC8s.
                1996 Dark Aubergine Escort Cosworth Lux with leather, GGR 305 chipped, GGR/Koni suspension, Black Diamond discs.
                2008 Orange/Black Westfield Megabusa, FW rear, Widetrack/Nitron Suspension, AP/Westfield 4 pots.
                Lots of Land Rovers!
                No wife or kids!!

                Comment


                • #9
                  Ha ha , nerdish has never been my strong point

                  Comment


                  • #10
                    Paul,

                    In simple terms,

                    "the relationship between the relative quantities of substances taking part in a reaction or forming a compound, typically a ratio of whole integers"
                    S54 Titan Silver metallic. Black leather, most factory options including sunroof, Becker Cascade and Becker Silverstone changer.

                    Comment


                    • #11
                      Originally posted by ian View Post
                      Passed MOT this morning, all good, no advisories.
                      However, Lambda reading was 1.03 (limit is 1.03!).
                      CO reading was 0.01 (limit 0.2) therefore very low - a good thing.
                      HC reading was 6 (limit 200ppm) so again very good.
                      CO = carbon monoxide, combustion product that becomes produced when there is not enough oxygen to burn the fuel into carbon dioxide (CO2)
                      HC = hydrocarbons, this is basically vaporized fuel that has been left unburned
                      Lambda = describes oxygen/fuel ratio and lambda = 1 equals optimal (stoichiometric) ratio when the amount of oxygen and fuel are in balance so that all fuel can be burned

                      The engine ECU makes adjustments according the 2 lambda sensors in the exhaust downpipes before the catalyzers. These sensors aim to maintain the oxygen/fuel ratio such the that catalytic converters are kept in their operation window and able to convert the environmentally harmfull NOx (nitrogen oxides) from the exhaust.

                      The MOT measurement is made from exit of the exhaust, which is after the catalyzers. Therefore this measurement only compares to the car's own lambda sensor readings if the exhaust system is completely airtight. A lambda sensor is basically a residual oxygen sensor measuring the remaining, residual oxygen content in the exhaust.

                      Your HC and CO readings indicate that the fuel has been completely burnt and thus there has been enough oxygen to oxidize all fuel (= hydrocarbons). The lambda reading of 1.03 indicates that you actually have a little bit more residual oxygen in your exhaust than optimal.

                      This could come from two reasons : 1) your engine is slightly underfueled (lean) or 2) air is leaking somewhere into your exhaust system.

                      However, the amount of extra residual oxygen is so low that should not be a reason to worry at all !

                      Typical reasons for lean mixture could be MAF (mass air flow) sensor fault/dirtiness (air going into engine incorrectly measured), air leak somewhere in the intake manifold system (after MAF) or some problem with one or more fuel injectors (not injecting the amount asked by ECU).

                      If you can hook your ECU into a simple reader, for example INPA, you can read out live data from your car's lambda sensors. If those give correct live readings and adjust the engine in real time correctly then there are no worries.

                      If during the MOT inspection also elevated idle values (2000-3000 rom) were taken and there the lambda value went closer to 1.000, then again no worries. At low idle any small amount of air penetrating into the exhaust system gives a hop to the lambda value. If at elevated revs lambda is correct then the engine is not suffering lean conditions.

                      I have played with these readings quite a lot when hunting down a problem which in the end was malfunction in the ECU unit itself. Changing the ECU unit cured the problem but before that I changed both lambdas, MAF and hunted for any air leaks in the inlet manifold and exhaust :)

                      Hopefully this helps.

                      - JuhaV
                      The older I get, the faster I was ...
                      BMW HP2 Sport
                      ex- BMW Z3 M Coupe - Cosmosschwartz Metallic

                      Comment


                      • #12
                        I was just wasting time reading the forums while the wife is watching Xmas movies not being serious guys

                        Comment


                        • #13
                          JuhaV

                          Thank you for the comprehensive note.

                          My EML light comes on every week or so (has done so for years) - does this clue help at all?

                          I read somewhere that BMW recommends replacing sensors at 100K miles. My car has done more than double that. Think I should get sensors replaced as a first step - not aware of any air leaks but will get the garage to check.

                          Thanks again,

                          Ian
                          S54 Titan Silver metallic. Black leather, most factory options including sunroof, Becker Cascade and Becker Silverstone changer.

                          Comment


                          • #14
                            Originally posted by JuhaV View Post
                            CO = carbon monoxide, combustion product that becomes produced when there is not enough oxygen to burn the fuel into carbon dioxide (CO2)
                            HC = hydrocarbons, this is basically vaporized fuel that has been left unburned
                            Lambda = describes oxygen/fuel ratio and lambda = 1 equals optimal (stoichiometric) ratio when the amount of oxygen and fuel are in balance so that all fuel can be burned

                            The engine ECU makes adjustments according the 2 lambda sensors in the exhaust downpipes before the catalyzers. These sensors aim to maintain the oxygen/fuel ratio such the that catalytic converters are kept in their operation window and able to convert the environmentally harmfull NOx (nitrogen oxides) from the exhaust.

                            The MOT measurement is made from exit of the exhaust, which is after the catalyzers. Therefore this measurement only compares to the car's own lambda sensor readings if the exhaust system is completely airtight. A lambda sensor is basically a residual oxygen sensor measuring the remaining, residual oxygen content in the exhaust.

                            Your HC and CO readings indicate that the fuel has been completely burnt and thus there has been enough oxygen to oxidize all fuel (= hydrocarbons). The lambda reading of 1.03 indicates that you actually have a little bit more residual oxygen in your exhaust than optimal.

                            This could come from two reasons : 1) your engine is slightly underfueled (lean) or 2) air is leaking somewhere into your exhaust system.

                            However, the amount of extra residual oxygen is so low that should not be a reason to worry at all !

                            Typical reasons for lean mixture could be MAF (mass air flow) sensor fault/dirtiness (air going into engine incorrectly measured), air leak somewhere in the intake manifold system (after MAF) or some problem with one or more fuel injectors (not injecting the amount asked by ECU).

                            If you can hook your ECU into a simple reader, for example INPA, you can read out live data from your car's lambda sensors. If those give correct live readings and adjust the engine in real time correctly then there are no worries.

                            If during the MOT inspection also elevated idle values (2000-3000 rom) were taken and there the lambda value went closer to 1.000, then again no worries. At low idle any small amount of air penetrating into the exhaust system gives a hop to the lambda value. If at elevated revs lambda is correct then the engine is not suffering lean conditions.

                            I have played with these readings quite a lot when hunting down a problem which in the end was malfunction in the ECU unit itself. Changing the ECU unit cured the problem but before that I changed both lambdas, MAF and hunted for any air leaks in the inlet manifold and exhaust :)

                            Hopefully this helps.

                            - JuhaV
                            JuhaV,

                            Thanks for that very informative reply. Exactly what I was wanting.

                            The bit that still puzzles me is this: since the figure of 1.03 shows excess oxygen/lean conditions and a complete "burn", why should that figure be the limit? Surely a figure showing too little oxygen or a rich mix would be worse for the environment because there would be any increase in HC and CO?
                            /// Exdos ///
                            "Men who try the impossible and fail spectacularly are infinitely superior to those who reach for nothing and succeed" --Napoleon Bonapart

                            Comment


                            • #15
                              I'm not sure what the lower limit is, but one would assume that it's .97, i.e. +/-3%.
                              Last edited by Limbs; 17-12-2013, 05:08 PM.
                              2000 Cosmos Black S50, Kyalami/Black interior, KW V3s, H&R ARBs, Supersprint exhausts, Apex ARC8s.
                              1996 Dark Aubergine Escort Cosworth Lux with leather, GGR 305 chipped, GGR/Koni suspension, Black Diamond discs.
                              2008 Orange/Black Westfield Megabusa, FW rear, Widetrack/Nitron Suspension, AP/Westfield 4 pots.
                              Lots of Land Rovers!
                              No wife or kids!!

                              Comment

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