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Failed Emissions - Low Speed. Miss at idle

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    Failed Emissions - Low Speed. Miss at idle

    Hey all,

    In my attempts to save this 318is I have ran into some emissions troubles. A month or so ago it failed the low speed sniffer test as follows:

    High Speed
    Reading Limit
    HC 157 180
    CO .82 1.20
    CO2 13.6
    O2 1.11

    Low Speed
    Reading Limit
    HC 465 180
    CO .87 1.20
    CO2 12.5
    O2 2.46

    When I took the car for the test I beat on it pretty good trying to get the cat hot but it was having overheating issues. I've since replaced the plugs, wires, done the mess under the intake cleanup with new vacuum lines and also fixed the overheating issues with new t-stat, radiator, fan clutch etc.

    The car runs well and has no idle surge but there seems to be a slight miss at idle. The car shakes a little sometime and emits an inconsistent exhaust burble when it does this. I'm afraid it won't pass the low speed again and I'm trying to figure out the next diagnosis step before wasting money on another emissions test only to fail. I can't seem to find any vacuum leaks by spraying carb cleaner around the lines. I'm not sure what to do next. Maybe the timing is off? I need to change the chain and guides soon anyway but it's pricey and I kind of wanted to make sure it passed emissions first. Any advice?

    Thanks!!
    Gabe
    '91 318is

    #2
    Do you have the original cat on the car?
    DENY IGNORANCE!
    Schwarz 325-totaled
    brilliantrot 318i-daily

    Originally posted by mkcman17
    don't think your hamster wheels are fast now. you will still have to give up when trying to pass that V6 odyssey to make your offramp.

    Comment


      #3
      As far as I know. That might be the next logical step.
      Gabe
      '91 318is

      Comment


        #4
        Also if your cars HC's are that high when slow driving I'd think you're running rich. Verify no vacuum leaks as it seems you have already done and your cat is also probably toast too. Spraying carb cleaner doesn't always work. I've found it only works on the intake boot and the intake manifold/throttle body.

        I'm leaning toward your cat being clogged.(restriction in exhaust). Do you get any backfiring or gurgling sound ever? Especially when getting on the gas and letting off? Do they do a vacuum test on the exhaust when you guys get tested?
        DENY IGNORANCE!
        Schwarz 325-totaled
        brilliantrot 318i-daily

        Originally posted by mkcman17
        don't think your hamster wheels are fast now. you will still have to give up when trying to pass that V6 odyssey to make your offramp.

        Comment


          #5
          I do think the car is running rich. At times I can smell it.

          I'm not sure if the "miss" at idle could be considered a burble or not. Now that you mentioned that it could be interpreted as one. There is no backfiring, however. The original muffler was toast, rattly and made awful noise. If the muffler backing was shot after all this time then the cat could be as well, like you said. They do not do a vacuum test at the emissions, just RPM and sniffer test.
          Gabe
          '91 318is

          Comment


            #6
            If your HC's are that high, depending on how long they've been that high, it's time for a new cat.

            Vacuum test would be the easiest to tell. High HC's come from being too rich or too lean
            DENY IGNORANCE!
            Schwarz 325-totaled
            brilliantrot 318i-daily

            Originally posted by mkcman17
            don't think your hamster wheels are fast now. you will still have to give up when trying to pass that V6 odyssey to make your offramp.

            Comment


              #7
              when i failed emissions i ended up getting a new cat (magnaflow). also got new o2 sensor and fixed all vac leaks.

              Comment


                #8
                Could be you have leaking injector(s), allowing fuel to drip at idle, ck this before blowing money on more expensive parts.
                Non contact IR thermometer should tell you at idle if you have a rich cylinder.
                CK temps of header tubes a couple of inch's from head. Rich cyl. will be considerably cooler. Engine should be at operating temp. for this.

                Comment


                  #9
                  Consider a compression/leakdown test. After doing a number of cheaper replacement items, those tests confirmed one of my exhaust valves went bad, which had caused a much more noticeable miss and ungodly HC numbers (~2700 ppm).
                  On Christ the solid Rock I stand, all other ground is sinking sand. (Edward Mote 1797-1874)

                  Comment


                    #10
                    Thanks for the help guys. I bought a universal flowmaster cat and welded it in. Passed with flying colors. Still having some issues with starting but at least it passed.
                    Gabe
                    '91 318is

                    Comment

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