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Failing Smog. Obd1 95’ M3

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  • Failing Smog. Obd1 95’ M3



    The car was sitting in storage for 2 years. It has 94k original miles. Now it has new injectors, fuel pressure regulator, fuel filter, fuel pump, o2 sensor, spark plugs, coil boots, air filter, intake manifold gaskets, vacuum lines, battery.

    Gas and all fluids were changed prior to ever starting it up.

    Failed CA smog on all 15mph gasses and triple the amount of NO. 25mph only fail HC.

    Reset the computer and drove for 30 miles. Took the car in with the cat as hot as possible and failed even worse. Latest numbers are as follows:

    15mph: HC 59max-220meas, CO .34max-.57meas, NO 486max-1975meas

    25mph: HC 36max-76meas, CO .33max-.17meas, NO 502max-57meas

    Any direction on where to look?

    Also has anyone scoped an obd1 o2? The waveform is really slow compared to what I’m used to. It takes about 4 seconds to cycle up and down. Same with the old and new sensor.

  • #2
    hows your valve cover gaskets? mine was leaking and the spark plugs were fouled with it. Only thing I bombed before changing out the plugs, valve cover, and gas door seal, was the 15mph HC test at Measured 82 (max 59). Afterwards I came in at 42 HC

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    • #3
      It’s leaking a little bit but I don’t see how that would get my HC up to 220 at 15mph.

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      • #4
        On the 95 M3, the magnesium valve cover likes to deform over the years. This causes oil to go into the spark plug hole which could cause the plug to not fire.

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        • #5
          Originally posted by OmairK View Post
          On the 95 M3, the magnesium valve cover likes to deform over the years. This causes oil to go into the spark plug hole which could cause the plug to not fire.
          that or more likely the seals that sit in the spark plug become so brittle that oil fouls up the plug. Those seem harden and get brittle than the valve cover premiter seal.

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          • #6
            Yup!

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            • #7
              Yea but these tube seals barely get a couple drops of oil on the coils. Spark plugs are new and the old ones weren’t covered in oil. Also no misfire the car runs great.

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              • #8
                Replaced the cat and all numbers dropped to almost 0. I am still failing HC at 25mph. Max is 36 I’m at 55. At 15mph I barely passed HC.

                I’m going to check for weak spark and compression. Fuel injectors and regulator are new. Any other ideas?

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                • #9
                  How is the crankcase hose that connects to the front of valve cover? Is it caked in oil?

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                  • #10
                    Originally posted by bmwstephen View Post
                    How is the crankcase hose that connects to the front of valve cover? Is it caked in oil?
                    Just pulled them off. Perfect shape just a little oil inside. No buildup.

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                    • #11
                      Compression test came out 178-197 across all 6 cylinders.

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                      • #12
                        Hmm. Have you tried the stomp test to see if any codes? Really running out of ideas here

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                        • #13
                          Originally posted by bmwstephen View Post
                          Hmm. Have you tried the stomp test to see if any codes? Really running out of ideas here
                          I have the obd1 adapter for my scan tool. No codes. I really wish it had fuel trim data. The coils are original so I’m gonna check for weak spark. After that maybe try a carbon treatment. Tops of pistons had a lot of buildup.

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                          • #14
                            New cats and new Ngk coils. Failing HC at 25mph. Max is 36 measured is 48. 15mph HC is 59max 55meas. All other gases are near 0. Co2 is around 14.5. Idk what to do running out of ideas.

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                            • #15
                              What plugs are you running out of curiosity?

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