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    Smog test Failed

    I recently got my car smogged at a STAR station and it failed....I talked with the technician and he told me it was my cat converter. So I took that with a grain of salt and went to get it diagnosed at another place and they told me my "front cat was running hotter than my back cat" all the while I was thinking to myself my car(88 325is) only has one cat converter? This through me off and any clarification would help. Also would I be better off just biting the bullet and getting a brand new cat converter? or finding a used one?Anyways long story short he told me to change the plugs and take it back and he's smog it and see if that would pass it.I am also attaching my results from the smog test.Thanks Top line is 15MPH bottom is 25MPH
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    #2
    I'm pretty sure what they meant to say was that the front of the cat is running hotter then the back of the cat. If that's the case and the car was brought up to proper operating temperature it is one indication of a failing catalytic converter. You should also be looking at your O2 sensor to make sure it is switching properly before flagging a bad converter. Just for the hell of it I ran a lambda calculation on the failed numbers and it looks to be running on the lean side which could be the reason the NOx number were higher and the HC was high enough to fail during the 15mph test which is why I mention the oxygen sensor. If I was still working as a smog tech I'd gladly throw it on the dyno and help you solve your problem but if you got to my old work the other smog tech has been at it since they started the smog program and would easily figure out your problem.

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      #3
      I'd say the O2 sensor isn't that old no more than 3 years. I don't drive my car that often being I have two motorcycles that I ride but I've had the car since I could drive and haven't ever replaced the cat and it just turned 30yrs. My next question is if I were to buy a cat brand new where could I take it where they could weld it up for me? Thanks for the quick reply. I had to pay a STAR tech 99.99 to tell me that my cat was bad haha kind of a punch in the junk.
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        #4
        Where in Socal are You? Everytime I smog an e30 I fill up with premium and get the cat really really hot then get smogged. That's done the trick with 5+ times

        If you are near Redlands I have friend who will do a pretest to see if it'll pass.
        Follow me on instagram @arda.e30

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          #5
          San Diego
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            #6
            Originally posted by ArdaMK2 View Post
            Where in Socal are You? Everytime I smog an e30 I fill up with premium and get the cat really really hot then get smogged. That's done the trick with 5+ times

            If you are near Redlands I have friend who will do a pretest to see if it'll pass.
            how much does your friend charge to do the pretest ? i just bought an e30 a week ago and need to see if it'll pass smog.. i'm in riverside

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              #7
              Don't buy a used cat for starters, you don't know what you are getting when buying used. I'm telling you because that's what I did and it was not good. Go to a muffler shop and bit the bullet for a new aftermarket cat, I was quoted 200.00 installed for a compatible aftermarket one.
              I am not sick, I am twisted. Sick makes it sound like there is a cure.

              1991 318is Diamantschwarz Metallic
              1989 325i Alpine White

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                #8
                Originally posted by TheRob View Post
                Just for the hell of it I ran a lambda calculation on the failed numbers and it looks to be running on the lean side which could be the reason the NOx number were higher and the HC was high enough to fail during the 15mph test which is why I mention the oxygen sensor
                I'm pretty sure he's running rich since his HCs (unburnt fuel) is so high and his CO and NOx are both very low.

                OP, did you drive for a while to ensure the cat was really warm? Also, are you burning oil in the engine?

                If your cat was warm, Some inputs to your DME for determining fueling are your O2 Sensor, Coolant Temp Sensor, Ambient Temp Sensor, and Throttle Position Sensor.

                I would check your plugs to make sure they look good and are correct, check your TPS to make sure it's set correctly and functioning for Idle/Mid/WOT, check to make sure the O2 sensor is working, replace the CTS with a BOSCH sensor if yours is old/not bosch, then maybe test your fuel pressure to ensure your FPR is working correctly.
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                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]

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                  #9
                  Originally posted by McGyver View Post
                  I'm pretty sure he's running rich since his HCs (unburnt fuel) is so high and his CO and NOx are both very low.
                  Its possible its running rich and the lambda calculator I used wasn't right but I used IATN's lambda calculator which is used by technicians nation wide and it gave me Lambda = 1.038 which is 15.26:1 AF ratio.
                  A lean condition can cause high HC as you're still not getting a complete burn (a lean misfire) and it will also cause the converter to work less efficiently and lead to a failure. Lean conditions don't always cause NOx emissions to shoot up too high, I've seen and fixed enough smog failures to have experienced this. I'm not trying to come off as condescending, please don't take it that way :)

                  I've fixed a lot of BMW's that customers thought had faulty converters and it was just a slow o2 sensor throwing the A/F mixture off.

                  OP you definitely should go through and check your ignition components, timing and other parts McGyver mentioned because they can all cause issues with passing smog and you don't want to spend the money getting a new converter installed if its something simple causing your problem and still have a failing car.

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                    #10
                    Originally posted by TheRob View Post
                    A lean condition can cause high HC as you're still not getting a complete burn (a lean misfire) and it will also cause the converter to work less efficiently and lead to a failure.
                    You know, I completely forgot about lean misfires. You're totally right.

                    Originally posted by TheRob View Post
                    I've fixed a lot of BMW's that customers thought had faulty converters and it was just a slow o2 sensor throwing the A/F mixture off.
                    This too. Most smog guys try to throw a cat at it, then the cat dies within 2 years since you just covered up the problem.
                    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]

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                      #11
                      @CR325IS
                      I recently had a very similar situation to yours. One of the reasons I think I had the issues because I took it to a new smog place due to the fact that the place I used to go just changed ownership.
                      The place I took it to did things a bit differently then my go to place. I had never failed smog test before with this vehicle, my car pass the 25 mile an hour test, but failed the 15 mile an hour test. I had driven the car hard and got the cat hot, but this new smog place let my car sit for 20 minutes then tested it and didn’t put a big fan in front of the car either as my previous place used to do that. I know the cat in the car is getting weak, but I decided to change the oil and I’m going to replace the spark plugs because they have about 47,000 miles on them. My oil also was in the car for more than one year even though I only had about 3800 miles on fully synthetic. I have a place that will do a pretest even though I paid the other place $50 for nothing.
                      Attached Files

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                        #12
                        Changed the plugs...there was oil on the other ones but I ended up buying a new cat. Gotta install it and take it back to smog. Thanks for the insight fellas...I'm trying to hold off and stack a few more chips before I buy a rebuilt head from bimmerheads.
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                          #13
                          How many miles should I put on my new cat before I smog it again?
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                            #14
                            At least around 100 miles. That's what i have done in the past and works for me. I have my smog coming up in April. I cringe up every time i see that smog due on my car. :(:( Usually it will need either or all oil change / spark plugs / O/2 sensor / cat converter. I have never had an issue with vacuum leaks.
                            Your signature picture has been removed since it contained the Photobucket "upgrade your account" image.

                            garage queen 91 bmw 325is / 1972 Chevy El Camino 355 sbc 450hp

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                              #15
                              Just passed with flying colors.
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