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    Help with smog result interpretation

    I am having trouble passing smog with my '84 635. The initial advice was to replace the cat. I did.
    It is still having high nox at 15 mph.
    I tried adjusting the spring 2 notches on the AFM to riches it up. Now 25 mph doesn't pass because too rich, and 15 mph is still too lean.

    Car just had a tuneup and the camshaft was worn.

    What else should I look at?

    (The papers have it as a 3.2 liter because it is '84. But it is a 3.5 liter Euro.)

    Sent from my VS995 using Tapatalk

    #2
    Are you getting the car really hot by running it on the freeway a while right before testing without turning the car off?
    "I'd probably take the E30 M3 in this case just because I love that little car, and how tanky that inline 6 is." - thecj

    85 323i M TECH 1 S52 - ALPINEWEISS/SCHWARZE
    88 M3 - LACHSSILBER/SCHWARZE
    89 M3 - ALPINEWEISS II/M TECH CLOTH-ALCANTARA
    91 M TECHNIC CABRIO TURBO - MACAOBLAU/M TECH CLOTH-LEATHER

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      #3
      Originally posted by reelizmpro View Post
      Are you getting the car really hot by running it on the freeway a while right before testing without turning the car off?
      My mechanic took it to the test. He did nit get the cat hot.


      But, isn't the problem that it is lean in the 15 mph test?

      What sensor in the car is different? The from is very similar, so the afm input should be similar. Is it the throttle position sensor input that is different?

      Sent from my VS995 using Tapatalk

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        #4
        Right, I was just curious if you got the cat nice and hot. It appears it's doing it's job. I would suggest running SeaFoam through the intake to try and get rid of any carbon build up especially if you haven't done it and it's a high mileage engine. Inadequate engine cooling also increases NOx. Change the coolant recently? If not, try an 70/30 mix of Distilled water/coolant. A trick is to run the heater and make sure the smog tech uses a fan in front of the car while testing as well. Is your car automatic?
        "I'd probably take the E30 M3 in this case just because I love that little car, and how tanky that inline 6 is." - thecj

        85 323i M TECH 1 S52 - ALPINEWEISS/SCHWARZE
        88 M3 - LACHSSILBER/SCHWARZE
        89 M3 - ALPINEWEISS II/M TECH CLOTH-ALCANTARA
        91 M TECHNIC CABRIO TURBO - MACAOBLAU/M TECH CLOTH-LEATHER

        Comment


          #5
          Originally posted by reelizmpro View Post
          Right, I was just curious if you got the cat nice and hot. It appears it's doing it's job. I would suggest running SeaFoam through the intake to try and get rid of any carbon build up especially if you haven't done it and it's a high mileage engine. Inadequate engine cooling also increases NOx. Change the coolant recently? If not, try an 70/30 mix of Distilled water/coolant. A trick is to run the heater and make sure the smog tech uses a fan in front of the car while testing as well. Is your car automatic?
          The temperature gauge looks to be in normal range, below half way.
          I have about 280K miles, but the head was replaced 30K miles ago.

          Car is a manual.

          Comment


            #6
            The disparity between 15mph and 25mph while running at about the same RPM's is strange. Have you considered trying another smog station?
            "I'd probably take the E30 M3 in this case just because I love that little car, and how tanky that inline 6 is." - thecj

            85 323i M TECH 1 S52 - ALPINEWEISS/SCHWARZE
            88 M3 - LACHSSILBER/SCHWARZE
            89 M3 - ALPINEWEISS II/M TECH CLOTH-ALCANTARA
            91 M TECHNIC CABRIO TURBO - MACAOBLAU/M TECH CLOTH-LEATHER

            Comment


              #7
              swap in the S38
              Simon
              Current Cars:
              -1999 996.1 911 4/98 3.8L 6-Speed, 21st Century Beetle

              Make R3V Great Again -2020

              Comment


                #8
                Originally posted by 2mAn View Post
                swap in the S38
                Yes, this option was discussed.

                Sent from my VS995 using Tapatalk

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                  #9
                  Have you tested the 02 sensor to see if its switching properly? It plays a very important roll in getting the cat to function properly. Is this a euro car with a euro DME? Because that could be a problem. If its a just a USDM car with a euro engine its fine. I spent a lot of time trying to diagnose a smog failure on a Porsche, it turned out to be an ROW euro market car and would never pass no matter what I did because cars in Europe from the 80s don't have the programming to use the 02 sensor to keep the cat working properly.

                  Comment


                    #10
                    Originally posted by TheRob View Post
                    Have you tested the 02 sensor to see if its switching properly? It plays a very important roll in getting the cat to function properly. Is this a euro car with a euro DME? Because that could be a problem. If its a just a USDM car with a euro engine its fine. I spent a lot of time trying to diagnose a smog failure on a Porsche, it turned out to be an ROW euro market car and would never pass no matter what I did because cars in Europe from the 80s don't have the programming to use the 02 sensor to keep the cat working properly.
                    that's a fucking interesting nugget of info! would a euro DME have a different label number?
                    sigpic
                    1987 - 325i Convertible Delphin Auto [SOLD], 325i Convertible Delphin Manual [SOLD]
                    1989 - 325i Convertible Bronzit m30b35 swapped [SCRAPPED], 325i Sedan Alpine Auto[DD]
                    1991 - 325i Coupe Laguna Manual [Project], 535i Sedan Alpine [SCRAPPED]

                    Comment


                      #11
                      Originally posted by McGyver View Post
                      that's a fucking interesting nugget of info! would a euro DME have a different label number?
                      I'm not sure, on that Porsche someone had wired in an 02 sensor to try and get it to pass but it did nothing. I'm just wondering if this is a grey market Euro car or has been swapped with a euro 3.5 running a euro DME. Mind you this was a Porsche and not a BMW but it could definitely play a roll. I know they used to use a separate fuel control module to federalize grey market Porsches.

                      Also the numbers always go rich when you hit 25 mph even if its just slightly rich. And like OP said, he adjusted the the AFM and now its good at 15 mph but theres a lack of fuel control at 25mph and prior to adjusting the AFM there was a lack of fuel control at 15 mph. Seems like a suspect 02 sensor possibly.

                      Test 1

                      15mph - AF ratio = 15.3/1 (lean)
                      25mph - AF ratio = 14.65/1 (slightly rich)

                      Test 2

                      15mph - AF ratio = 14.7- stoich (perfect)
                      25mph - AF ratio = 14.36 - rich
                      Last edited by TheRob; 09-12-2018, 08:26 AM.

                      Comment


                        #12
                        Originally posted by TheRob View Post
                        Have you tested the 02 sensor to see if its switching properly? It plays a very important roll in getting the cat to function properly. Is this a euro car with a euro DME? Because that could be a problem. If its a just a USDM car with a euro engine its fine. I spent a lot of time trying to diagnose a smog failure on a Porsche, it turned out to be an ROW euro market car and would never pass no matter what I did because cars in Europe from the 80s don't have the programming to use the 02 sensor to keep the cat working properly.
                        It is a gray market car. I have passed smog in the past, but it is always a struggle.

                        The O2 sensor does change, and the car runs differently if it is unplugged. My mechanic thinks the O2 sensor is working. I have a volt meter hooked up to the O2 wire and can see it changing values as I drive, and it behaves differently after I adjusted the AFM to richen it up.

                        The ECU is an 011. And it has the low impedance injectors. I didn't think the ECU had an O2 input, but it is wired into the ECU (it was spliced in).

                        I was thinking that the AFM would be at the same value at both the 15 and 25 MPH tests because the RPM is similar. But after thinking about it, the throttle would be open more, and that would let more air in (to get more power for the 15 MPH test, they say it is twice the power required for he lower speed test).

                        Out thoughts are that it is either the AFM, or the ECU. (But maybe it is worth trying a new O2 sensor. I have replaced it, but can't remember when.)

                        Comment


                          #13
                          Originally posted by Tinkerer007 View Post
                          It is a gray market car. I have passed smog in the past, but it is always a struggle.

                          The O2 sensor does change, and the car runs differently if it is unplugged. My mechanic thinks the O2 sensor is working. I have a volt meter hooked up to the O2 wire and can see it changing values as I drive, and it behaves differently after I adjusted the AFM to richen it up.

                          The ECU is an 011. And it has the low impedance injectors. I didn't think the ECU had an O2 input, but it is wired into the ECU (it was spliced in).

                          I was thinking that the AFM would be at the same value at both the 15 and 25 MPH tests because the RPM is similar. But after thinking about it, the throttle would be open more, and that would let more air in (to get more power for the 15 MPH test, they say it is twice the power required for he lower speed test).

                          Out thoughts are that it is either the AFM, or the ECU. (But maybe it is worth trying a new O2 sensor. I have replaced it, but can't remember when.)
                          Its not just that the 02 changes but how quickly it changes. If your 02 slows down the AF ratio is thrown out of balance and yes at 25 mph you are under more load so you are getting more air. If its switching at a slow pace under steady state cruising you're likely looking at a faulty 02 sensors. It's all about balance and if something is out of balance with fuel control it changes everything.

                          Comment


                            #14
                            Originally posted by TheRob View Post
                            Its not just that the 02 changes but how quickly it changes. If your 02 slows down the AF ratio is thrown out of balance and yes at 25 mph you are under more load so you are getting more air. If its switching at a slow pace under steady state cruising you're likely looking at a faulty 02 sensors. It's all about balance and if something is out of balance with fuel control it changes everything.
                            I think the 15 MPH test is more load than the 25 MPH test. I searched the internet and found this reference:
                            There are four parts to the smog test. 1) Vehicle Identification The smog test technician will enter your VIN number, Odometer reading a...

                            ++++++++++++++++++++++++++++++++
                            The 50/15 test in which the automobile is subjected to 50% of maximum engine load conditions, encountered at the Federal Test Procedure, at 15 mph. Next the 25/25 test is executed where, as you might have guessed, the vehicle is run at 25 mph at 25% load conditions.
                            ++++++++++++++++++++++++++++++++

                            I guess I will try a new O2 sensor.

                            Thanks for the comments.

                            Comment


                              #15
                              Yep had a bit of a brain fart there, lol, one of the reasons I don't post before noon...foot meets mouth.
                              Last edited by TheRob; 09-12-2018, 12:21 PM.

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