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Stumped by obd2 check engine faults. Could use some help!

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    Stumped by obd2 check engine faults. Could use some help!

    Hey folks-

    I have been chasing down a problem for weeks that I can't seem to figure out. Car is a 325is with S52, OBD2. I'm also running the Turner M50 manifold adapter kit for OBD2. My car is running the 2 preCat O2 sensors only. The postCat sensors have been flashed out. Car has run for several years w/o throwing codes but now I keep getting combinations of the following faults:

    - preCat O2 sensor voltage, Cyl # 1-3
    - O2 sensor control limit, Cyl # 1-3
    - O2 sensor control limit, Cyl # 4-6
    - O2 sensor adaptation limit, Cyl # 1-3
    - O2 sensor adaptation limit, Cyl # 4-6

    I felt like everything pointed to a vacuum leak, so I removed, checked, and reinstalled all of the lines. I smoke-tested and discovered that I had a blown dipstick tube o-ring and a very slight leak at the seal between the CCV and the intake. I replaced both of those seals expecting the problem to go away, but the same codes persisted. Just to be even more thorough, I replaced the CCV and all related lines and seals, as well as the O2 sensors. None of that made a difference. The car idles and runs perfectly, not exhibiting any misses and the power delivery is smooth and 'normal' feeling. The codes I listed are taken from my Peake reader but I've also connected to the ECU via my Torque app on my phone to compare the readings. The codes have slightly different descriptions but seem to be consistent with what the Peake is reporting. There is one very strange thing, though. Torque is showing a consistent 0% reading for the short term fuel trims on both banks. However, to be fair I'm not 100% sure that the converter cable that connects my engine compartment round connector to my bluetooth OBD reader can be trusted. All other realtime data is showing properly in Torque, but the fuel trims are not changing. Could this be a clue? If so, is it possible I have an issue with my ECU maybe or even the wiring? I have confirmed I'm getting voltage to both of the O2 sensors. At this point I'm totally stumped and would appreciate any insight y'all can share!
    '90 325is/S52
    '76 2002
    '74 2002tii
    '06 325i sedan
    '05 X5 3.0i
    '86 Alfa Spider Veloce

    #2
    Do you have a laptop/cable with a working INPA install?

    Wondering if you could match up the generic codes with the MS41 DTC that INPA or a BMW specific scanner would spit out (There are 35 Lambda codes on that list, some will say if the limit is Max or Min)

    BMW Siemens MS41, MS42 and MS43 Fault codes. BMW M52TU and M54 petrol engine fault codes. (E34, E36, E38, E46.) 1 Ignition coil Cyl 2 2 Ignition coil Cyl 4 3 Ignition coil Cyl 6 5 Fuel injector Cyl 2 6 Fuel injector Cyl 1 8 Air Flow Meter (HFM) 10 Coolant Temperature Sensor 11 Tank Pressure Sensor


    Usually when these cars bump into adaptation limits, it's because the O2 sensors are plugged into the wrong banks and creates a logic feedback loop where the ECU sees Bank 1 rich, pulls fuel, then sees Bank 2 lean and adds fuel, and cycles like this until it hits the Max/Min limits and throws the limit codes.

    If you kept your old post-cat O2 sensors, maybe you can swap one in the bank 1 slot and see if it fixes the voltage code? The first code could just be a bad sensor.
    Originally posted by priapism
    My girl don't know shit, but she bakes a mean cupcake.
    Originally posted by shameson
    Usually it's best not to know how much money you have into your e30

    Comment


      #3
      Originally posted by Northern View Post
      Do you have a laptop/cable with a working INPA install?

      Wondering if you could match up the generic codes with the MS41 DTC that INPA or a BMW specific scanner would spit out (There are 35 Lambda codes on that list, some will say if the limit is Max or Min)

      https://sites.google.com/site/openms...uble-codes-dtc

      Usually when these cars bump into adaptation limits, it's because the O2 sensors are plugged into the wrong banks and creates a logic feedback loop where the ECU sees Bank 1 rich, pulls fuel, then sees Bank 2 lean and adds fuel, and cycles like this until it hits the Max/Min limits and throws the limit codes.

      If you kept your old post-cat O2 sensors, maybe you can swap one in the bank 1 slot and see if it fixes the voltage code? The first code could just be a bad sensor.

      Hey Northern thanks so much for the reply. So I decided to swap the O2 sensor banks again and see what happened, since I hadn't swapped them since finding the most recent vacuum leak... I still have codes, but now I'm only getting 2... According to INPA:

      202 Lambda Regulation Bank 1 Post Cat

      203 Lambda Regulation Bank 2 Post cat


      According to my Torque OBD reader app:

      P0170 - Powertrain - Fuel Trim (Bank 1)
      P0173 - Powertrain - Fuel Trim Malfunction (Bank 2)

      So now this is confusing to me. If my post cat O2 sensors were flashed out of my tune, why would INPA be seeing post-cat faults?

      I'm not sure if this is another clue, but this is also happening. When I clear codes and first start the car, it runs for a good couple minutes without throwing codes. But then I notice what sounds like a 'hissing' or 'spraying' sound coming from the area where the fuel pressure regulator is attached to the fuel rail input tube. I can't pinpoint where it's coming from exactly, but it could even be coming from the number 5 or 6 injectors... It's really hard to tell. But the point is, after I start hearing that hissing sound, then the car throws the codes. Of course, this could just be a coincidence....

      Light any bulbs for you?

      EDIT: here is the INPA screenshot. Unfortunately I can't read German....
      Click image for larger version

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      Last edited by RenaissanceMan; 03-16-2023, 03:13 PM.
      '90 325is/S52
      '76 2002
      '74 2002tii
      '06 325i sedan
      '05 X5 3.0i
      '86 Alfa Spider Veloce

      Comment


        #4
        I had weird experiences with OBD2 P codes not really lining up with what INPA says. I don't really have any reason for this, but I usually trust INPA.

        I feel like I've heard these two codes happen on cars with the PC O2s flashed out before.
        I know back in the day, EWS and Emissions deletes were pretty crude with hard mods to the PCB and "FF"ing whole sections of code, and there are still ebay sellers who never bothered to stop doing it that way. Do you know who did your tune?


        With the noise right at the FPR, assuming the vacuum line itself is good, the FPR could've failed? Would make more sense with pre-cat O2 codes though.
        Originally posted by priapism
        My girl don't know shit, but she bakes a mean cupcake.
        Originally posted by shameson
        Usually it's best not to know how much money you have into your e30

        Comment


          #5
          I keep hitting a wall with this.. I ended up replacing the FPR and all of the intake manifold gaskets. Same problem. Keep getting same codes from Torque:

          P0170 - Powertrain - Fuel Trim (Bank 1)
          P0173 - Powertrain - Fuel Trim Malfunction (Bank 2)

          One other thing to note is that if I clear the codes and monitor realtime data, short term fuel trims on both banks shoots up to +25% before throwing codes and going to 0.00%. It's thinking it has excess air from somewhere, but I've checked for vacuum leaks exhaustively with none showing up. Could a wiring harness short or a bad ECU cause this type or behavior?​
          '90 325is/S52
          '76 2002
          '74 2002tii
          '06 325i sedan
          '05 X5 3.0i
          '86 Alfa Spider Veloce

          Comment


            #6
            What are you running for injectors? Pink tops? if not, I'd swap to them.
            Can you measure fuel pressure somehow? make sure it's 3.5bar with the FPR vacuum unhooked, and less than that at idle with the FPR plugged in.

            Check the ECU connector for resistance or short to GND. Basically go in the ETM for a 328/M3 and look at the X6000 pinout and make sure each pin has continuity and nil resistance to one pin on the O2 connectors and no shorts between or GND.

            If that doesn't work, maybe pop the ECU open and see if there's anything physically fried, or just try a different ECU if you can?

            Could also be on the MAF side, if the MAF is bad (or wrong) and showing less airflow than actual.
            Originally posted by priapism
            My girl don't know shit, but she bakes a mean cupcake.
            Originally posted by shameson
            Usually it's best not to know how much money you have into your e30

            Comment


              #7
              Originally posted by Northern View Post
              What are you running for injectors? Pink tops? if not, I'd swap to them.
              Can you measure fuel pressure somehow? make sure it's 3.5bar with the FPR vacuum unhooked, and less than that at idle with the FPR plugged in.

              Check the ECU connector for resistance or short to GND. Basically go in the ETM for a 328/M3 and look at the X6000 pinout and make sure each pin has continuity and nil resistance to one pin on the O2 connectors and no shorts between or GND.

              If that doesn't work, maybe pop the ECU open and see if there's anything physically fried, or just try a different ECU if you can?

              Could also be on the MAF side, if the MAF is bad (or wrong) and showing less airflow than actual.
              Yep, I'm running pink top injectors.

              Measured fuel pressure earlier today with my Harbor Freight tester. Have no idea how accurate it is, but I'm getting 3.3 bar with the vacuum line disconnected from the FPR, and 2.9 bar with the line connected. Both measurements taken at idle at about 800 rpm. Also swapped out a used MAF today and got the same results. Thanks for the suggestion on the ECU connector ground. I'll try that and looking at the opened ECU next.
              '90 325is/S52
              '76 2002
              '74 2002tii
              '06 325i sedan
              '05 X5 3.0i
              '86 Alfa Spider Veloce

              Comment


                #8
                Re-reading what I wrote, I think I should clarify that I meant only the O2 sensor pins, should be 8 for the two pre-cat O2 sensors. Each wire should be a straight run from O2 plug pin to ECU pin IIRC
                Originally posted by priapism
                My girl don't know shit, but she bakes a mean cupcake.
                Originally posted by shameson
                Usually it's best not to know how much money you have into your e30

                Comment


                  #9
                  Had something interesting happen yesterday after a short test drive. Noticed a burning smell that smelled electrical to me and saw some smoke coming from the engine compartment drivers side right in front of the firewall. Looked with a flashlight and felt around all the wiring, harness, fuse box, etc in that area but didn’t feel any hot spots and couldn’t tell the source. Maybe it wasn’t wiring but it sure smelled like it. I’m really starting to think I have a short somewhere or something. Anxious to do the continuity test on the O2 harness wiring.
                  Last edited by RenaissanceMan; 04-01-2023, 06:50 PM.
                  '90 325is/S52
                  '76 2002
                  '74 2002tii
                  '06 325i sedan
                  '05 X5 3.0i
                  '86 Alfa Spider Veloce

                  Comment


                    #10
                    Latest updates:

                    I downloaded the ETM for my motor and continuity tested all of the harness wires connecting the O2 sensors to the ECU. Also checked to make sure I had 12v at the O2 sensors and checked the grounds. All normal. Smoke tested one more time to make sure I had no leaks. But then I found something interesting... After clearing the fuel mixture codes, I discovered that the codes would return when just turning the key to "on" without cranking the car. In other words, the ECU is reporting fuel mixture data before it should even have gotten any of that data. For that reason, I'm assuming I have a problem with my ECU. Would y'all agree?​
                    '90 325is/S52
                    '76 2002
                    '74 2002tii
                    '06 325i sedan
                    '05 X5 3.0i
                    '86 Alfa Spider Veloce

                    Comment


                      #11
                      I'm not saying it isn't your ECU, but I don't think clearing codes works to reset adaptations.
                      I wonder if the LTFT adaptations are saved at their limit where they trigger the DTC code, and as soon as the ECU gets power it throws the code again.

                      Did you reset adaptations with INPA (or other code reader if it has that functionality)
                      Personally I do this with Romraider Logger because it can display and reset TPS/Idle Fuel/LTFT/knock adaptations and I already use it to datalog.
                      It can be a pain to set it up the first time though.
                      Originally posted by priapism
                      My girl don't know shit, but she bakes a mean cupcake.
                      Originally posted by shameson
                      Usually it's best not to know how much money you have into your e30

                      Comment


                        #12
                        Originally posted by Northern View Post
                        I'm not saying it isn't your ECU, but I don't think clearing codes works to reset adaptations.
                        I wonder if the LTFT adaptations are saved at their limit where they trigger the DTC code, and as soon as the ECU gets power it throws the code again.

                        Did you reset adaptations with INPA (or other code reader if it has that functionality)
                        Personally I do this with Romraider Logger because it can display and reset TPS/Idle Fuel/LTFT/knock adaptations and I already use it to datalog.
                        It can be a pain to set it up the first time though.
                        These are great points, and no I didn't reset adaptations. I will clear those with the codes and test again and post back.
                        '90 325is/S52
                        '76 2002
                        '74 2002tii
                        '06 325i sedan
                        '05 X5 3.0i
                        '86 Alfa Spider Veloce

                        Comment


                          #13
                          Ok folks, wanted to report back with an update.

                          First of all, I think I located the cause of the short that I was smelling. There were 2 soldered harness splices on power wires from the e30/e36 connections to the relay block that were somewhat broken, and looked like they would have possibly have been making intermittent connection. Got those cleaned up and resoldered and so I can at least check those connections off the list.

                          Secondly, clearing adaptations did indeed prevent the faults from showing up again after just turning the key, so once again I'm able to start from a 'clean slate' after clearing codes.

                          Thirdly, I purchased a new MAF to rule out the unlikely possibility that both of my used MAFs were not functioning correctly.

                          I started using INPA only for monitoring the faults so I wasn't chasing codes in an inconsistent manner. Having said that, I'm still getting the same fuel trim faults. Here is a summary of what is happening consistently after I clear the codes and adaptations and start the car from cold:

                          1. Start the car - car idles perfectly
                          2. There is a 5 or so minute period which I'm assuming is the waiting for readiness period that I'm not seeing any fuel trim data being logged in INPA
                          3. After this 5 or so minute period, 'lambdaintegrator 1' and 'lambdaintegrator 2' readings go from 0 up to 64 and stay there for at least a minute or 2
                          4. After this minute or 2, both of these values will then return to 0. That is when the car will throw fuel trim codes for pre-cat sensors on banks 1 and 2 (202 fuel trim limit Bank 1
                          and 203 fuel trim limit Bank 2)
                          5. At no time do the 'adaptation value additive' or 'adaptation value multiplicative' values EVER move from 0. I have to assume this is a significant clue, since I should be seeing some kind of adaptation adjustments being made after the car has warmed up??

                          I've attached the 3 analog value pages from INPA that I screen-shot after the 5 or so minute warm up period. Another possible clue is that both the 'load [mg/stroke]' and 'needed air i.s. controller [kg/h] values are pegged with an exclamation point. (see analog 1 value page)

                          I could use some feedback if y'all have some insight.

                          Once again, here's a summary of everything I've done:

                          - smoke tested repeatedly
                          - replaced ccv and all seals/hoses
                          - replaced O2 sensors
                          - continuity and voltage tested all O2 sensor wiring
                          - replaced MAF
                          - replaced intake manifold gaskets
                          - replaced fuel pressure regulator
                          - verified temp sensor readings as normal

                          I feel like the only thing left to replace is the ECU, right? I'm really getting frustrated with this.

                          '90 325is/S52
                          '76 2002
                          '74 2002tii
                          '06 325i sedan
                          '05 X5 3.0i
                          '86 Alfa Spider Veloce

                          Comment


                            #14
                            Just smoke-tested the exhaust. No leaks from the headers or gaskets where they meet the head. However, I'm not sure if this is an accurate enough test unless I'm closing off the valves for each cylinder. Maybe y'all can chime in on that. What I do have is a leak at the gaskets where the collector bolts to the exhaust. And this leak is only about 2" behind the bungs for the O2 sensors. Even though it's behind the sensors, would a leak in that close a proximity cause a possible anomaly in what they are reading?
                            '90 325is/S52
                            '76 2002
                            '74 2002tii
                            '06 325i sedan
                            '05 X5 3.0i
                            '86 Alfa Spider Veloce

                            Comment


                              #15
                              Sorry, I haven't checked r3v in a bit.

                              Originally posted by RenaissanceMan View Post
                              2. There is a 5 or so minute period which I'm assuming is the waiting for readiness period that I'm not seeing any fuel trim data being logged in INPA
                              Makes sense, ECU doesn't enable STFT until something like 80 degC coolant temp.

                              Originally posted by RenaissanceMan View Post
                              5. At no time do the 'adaptation value additive' or 'adaptation value multiplicative' values EVER move from 0. I have to assume this is a significant clue, since I should be seeing some kind of adaptation adjustments being made after the car has warmed up??
                              So the "Additive" is idle fuel trim, "Multiplicative" is the Long Term Fuel Trim (LTFT). Takes a bit for it to start increasing/decreasing these based on average lambda integrator value.

                              I wouldn't be surprised if there's some logic built in so that it refuses to store either of these if the lambda integrator isn't behaving a specific way.

                              Any opinion of whether it runs better or worse while the lambda integrator is pegged?


                              At this point unless you have a wideband to show the fueling is somehow way off, I'd say it has to be the ECU.

                              I'm not sure if the load/ICV values are normal like that. My car isn't together enough to check.

                              Originally posted by priapism
                              My girl don't know shit, but she bakes a mean cupcake.
                              Originally posted by shameson
                              Usually it's best not to know how much money you have into your e30

                              Comment

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