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M20 Turbo running lean/wastegate opening early

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    M20 Turbo running lean/wastegate opening early

    Currently trying to tune my M20 turbo, having an issue with it going lean (18:1) under load ect. Accel enrich and ego control are off.

    The wastegate also opens around 107KPA. The spring is meant to be a 7PSI, haven't bench tested it though. Boost control was turned off during the log. Not sure if thats related or a separate issue.

    I've never tuned before so I'm not sure how to use the log to work out the issue. Could someone have a look for me please? Log was about 30mph max 1st/2nd gear.

    M20B25 9.7:1
    HX35 16cm
    44mm ebay gate
    630cc injectors
    wasted spark
    megasquirt 2
    timing verified with light

    Link here with datalog and tune.



    #2
    im not an expert , but the values in the ms seems to be gentle , i vas watching the log , and i can sugest you 2 things , 1 if the WB has a calibration prosses . do it to re calibrate it . 2 taking in consideration , the WB task its meseaure the precence of OXygen on the combustion . the explaniation i can suggest its the AFR goes hi coz you flood it with fuel. that can explain why it goes the AFR goes hi. dont forget you run 630cc and having 5ms it could be enough to flood it , taking in consideration its not camming turbo presure yet , you at 4600RPM start to build pressure.Click image for larger version

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      #3
      Yeah I can try calibrating the sensor again, but I bought it new and not run much with it.

      If there was too much fuel, would the number not show rich eg9:1?

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        #4
        I've now done a free air calibration on the sensor.

        Checked the wastegate with a compressor, it did open around 1PSI. I've put the second biggest spring in, was around 7PSI with the compressor.

        I did another log with nothing changed but the spring and calibration. Now getting 126KPA before hearing the wastegate. Didn't want to keep accelerating as AFR was at 18.

        I used VE analyze on that log to adjust the MAP. It added more fuel, I did another log with that tune. Saw 140KPA but AFR still went to 18.

        If it was over fueling so much it didn't burn the mixture I would think there would be a lot of black smoke, I'm not getting any. Doesn't feel like its missing either.

        I have a link with both logs and VE analyze adjusted tune here.

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          #5
          do you check the Fuel presure?? maybe you are down to 3bars and with big injectors you make a drop to the pressure for the fuel . on the logs it seems to be a bit better now at least at the beginning the afr stays at 14 . if you are on the stock fuel pump im not remember but its 162l/h and worse if it is aged or in his EOL.

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            #6
            I don't have a gauge to check it, but the pump is a new AEM 320LPH with a dedicated feed from the battery so should be fine.

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              #7
              What waste gate are you using?

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                #8
                It's a 44mm Tial style copy.

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                  #9
                  1) I don't know if your TPS is calibrated properly, it shows a max of 54% in your log.
                  2) Are you sure you don't have a massive boost leak?
                  3) If you plan to use your AFR table to tune, enable "Incorporate AFR Target" in General settings.

                  The rest looks ok to me, just needs to be tuned. I would start by throwing 30% more fuel in the table above 3101.
                  '84 318i M10B18 147- Safari Beige
                  NA: 93whp/90ftlbs, MS2E w/ LC, 2-Step
                  Turbo: 221whp/214ftlbs, MS3x flex @ 17psi

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                    #10
                    The TPS is calibrated, in that log I didn't use full throttle.

                    Confident I don't have a boost leak but I have an adapter coming to make sure. Ordered a fuel pressure gauge as well.

                    I thought it was best to leave the AFR table disabled until the tune was closer? May be wrong.

                    Yeah I'll try more fuel, will probably wait till I've confirmed fuel pressure and no boost leak.

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                      #11
                      If you leave the AFR table disabled as soon as you turn it on it will add/remove fuel from your map depending on the difference from stoich (14.7). If you add it now you tune to the table and then if you'd like to make adjustments later you just change your AFR table and don't have to retune the VE. Right now the AFR table has no adjustment on your base fuel map. It's fine if you never re-tune the car and know your target AFRs may not match what your VE table is tuned for
                      '84 318i M10B18 147- Safari Beige
                      NA: 93whp/90ftlbs, MS2E w/ LC, 2-Step
                      Turbo: 221whp/214ftlbs, MS3x flex @ 17psi

                      Comment


                        #12
                        OK I've enabled it and set up the AFR table. After some autotune it doesn't go as lean but it's not meeting the AFR target. Does that mean the VE needs increased at those load points?

                        Also having an issue with high idle after hot starts. Sometimes the engine will run on after being turned off (when idling high). Looking at the log, it looks the the idle valve is open, but the coolant is above the temperature for it to be active so not sure why. It starts at 40% then tapers down.

                        Checked for boost leaks, found a few at 30PSI, sorted all bar one from the top of the throttle body shaft. It looks like the seals are part of the needle bearings.

                        Fuel pressure is sitting around 40PSI at idle. I haven't set up a camera yet to watch it while driving.

                        I have a log of the drive with AFR enabled and a hot start. I had to use flood clear as it wouldn't start at first hence the 100% throttle.

                        Comment


                          #13
                          Yes, VE needs to be bumped up. autotune will only do so much until the O2 sensor is out of range. And it's best to start rich and take fuel out rather than doing lean pulls and adding fuel.

                          Megasquirt does not extrapolate table values. It will used the last value on the table if you are "outside" of that value. For example, this is why you must have WUE at 100% once you reach your target temp otherwise it will add/remove a percentage of fuel on top of the rest of the fuel calculations. The same applies for 1D tables like idle PWM values.

                          Here's a revised tune with some tweaked cranking settings and an enriched fuel table. It should give you a little more progress to your final tune.


                          Nice job having boost cut setup at 160kpa. Don't ever disable it completely unless you want to live dangerously.
                          '84 318i M10B18 147- Safari Beige
                          NA: 93whp/90ftlbs, MS2E w/ LC, 2-Step
                          Turbo: 221whp/214ftlbs, MS3x flex @ 17psi

                          Comment


                            #14
                            OK that makes sense.

                            I'll try that tune, as long as I can get a reliable idle and can put the car in for inspection then I can properly drive it rather than going round the block.

                            Yeah until I can get to a dyno I didn't want to risk it.

                            Thanks for your help will hopefully get it on the road this year.

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