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    Chip tunes and emissions

    So my 1986 325e (2.5 swapped) failed emissions today. I think it’s because I didn’t take the chip out before getting it tested. When I purchased the car a few weeks ago, the seller gave me two additional chips with it: one for a 325ix and the other stock. Can anyone help me figure out which one is which?


    #2
    i have the same setup as you and i pass fine. my motor also has bigger injectors and a performance head. maybe you need to beat on it and get the cat real hot before you smog

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      #3
      It is not the chip. The car will be running in closed-loop (using O2 sensor feedback) mode during emissions tests. The only way that your mixture could be that far off is if the O2 sensor is dying, o the injectors were changed to something very different than stock (and you would likely see a CEL due to the O2 sensor reporting out-of-bounds AFR). Granted, all of this assumes you have a car with an O2 sensor & cat.

      The most likely culprit is a crapped-out catalytic converter, dying O2 sensor and/or vacuum leaks. What were the numbers from your test?

      Regarding which chip is which, there were like a dozen versions used in Motronic 1.3 for the M20 engine. There will be very little functional difference between an "i" and "iX" tune as far as emissions are concerned.

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        #4
        Thanks for the help. I suspect you’re on to something with the 02 sensor or vacuum leaks. The cat is brand new so I doubt that’s it. Regardless, here are the numbers:

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          #5
          High HC AND high NOx together are usually caused either by a bad cat (which it sounds like is not an issue for you) or pre-detonation/knock. How many miles are on the engine? Also, what kind of cat did you have installed? Really cheap after-market ones often cheap-out on the elements used to scrub emissions. If the PO told you that the cat was new / recently installed, they may have been lying. A dying cat is almost always the cause of high HC and high NOx. If you can get the car up on stands, snap a pic of the cat that is on there and post it.

          A vacuum leak usually causes lean running and just high NOx, although if the O2 sensor is working properly it should run fairly clean unless the leak is REALLY bad. How is the idle quality?

          A dying O2 sensor usually causes rich running, occasionally lean running. Rich usually means high HC, and lean means high NOx. Again, being high in both is usually something else.

          If the cam or ignition timing is off, you could also fail emissions, but you'd have to check the mechanical timing of everything to rule that out. If the previous owner of the motor modded it, then it could be that stuff is out of adjustment.

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