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    Clogged Cat?

    I'm thinking I have a clogged cat. Here are the symptoms:

    - Car seemed to be down on power last weekend at a 2 day HPDE I attended.
    - White ash/residue inside of tail pipe.
    - Sound of exhaust is a bit more muted.
    - I got under the car today and saw this, the exhaust from headers to cat is white in color:

    20190914_103039 by mike.bevels, on Flickr

    The car is idling fine. The only temp gauge I have is the factory coolant gauge, which reads normal. Think it's time to replace the cat (145K miles, possibly original)?

    Anyone know of a good factory-style replacement for a 1991 318is?

    #2
    You may want to take the cat back off and stick a flashlight into the cat? When I was having CPS issues we originally thought it was the cat, but after taking a look inside things were clean. Aftermarket catalytic converters donít tend to last long, though, from what I hear...in CA they get you through maybe one smog check (2 years). Sent from my iPhone using Tapatalk
    Current flame: E30 318iS Alpinweiss II slicktop / LSD - Joanne
    The ex: E92 335i 6MT M-Sport - Betty
    The heavy: 2001 4Runner SR5 Sport (3rd Gen) - Fred

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      #3
      So after some testing with a temp gun and vacuum gauge, I decided to suck it up and pull the cat-back to inspect the cat. The temp gun read 60 degrees hotter after the cat (good). The vacuum gauge operated normally as if there wasn't a blockage (good). The matrix inside the cat looks good. Though I'm not sure if the "mess" at the top and bottom are normal. I assume that's how they are packaged. the center section of the matrix looks good to me. Thoughts on the photo below?

      20190922_091946 by mike.bevels, on Flickr

      I did track down a small intake leak, which could explain why the car seemed to be down on power. I'll see how the car behaves this week when I'm driving it.

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        #4
        If cats clog, they tend to clog at the front of the ceramic monolith.
        You'd need to inspect the front side which is a PITA
        (Down pipe off with a borescope or through the O2 sensor hole with borescope)

        The 'mess' at the top and bottom is most likely the mounting matting that expands after initial burn in to keep the monolith in place.

        Hard to tell.
        Yes, fix the intake leak.
        - did you change anything for your weekend (e.g. Gas, fuel additives)?

        E30 320i vert
        But daily drive is Volvo V60 Polestar

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          #5
          Originally posted by Tzantushka View Post

          Hard to tell.
          Yes, fix the intake leak.
          - did you change anything for your weekend (e.g. Gas, fuel additives)?
          Thanks, I was also thinking I need to inspect it from the front.

          I have fixed the intake leak. The car seemed to have a bit more power, but it was also 20 degrees cooler out, so I'll need to drive it more to see.

          I haven't changed anything else. No additives. Same gas from the same station for the last few fill-ups.

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