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This is a discussion on Catalytic converter overheating? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Originally Posted by dttruax Just doing a quick parts search. Which part needs to be replaced? http://subarupartsforyou.com/cp_part...nly+&year=2004 The uppipe is ...

  1. #16
    OMG WTF MainFrame's Avatar
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    Quote Originally Posted by dttruax View Post
    Just doing a quick parts search. Which part needs to be replaced?

    http://subarupartsforyou.com/cp_part...nly+&year=2004


    The uppipe is labled "H" in this diagram:

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    Quote Originally Posted by SD_GR View Post
    On my phone the link won't load. However, because it's a lot of work to change the up pipe I recommend the question be reversed: you tell us the part that had failed. A "square" mechanic may not know what the "up pipe" is.

    Are you sure it's the up pipe? Just checking to save headaches, not trying to be a pain.
    My mechanic said that is the "front catalytic converter". EJ527 stated here that the "front CC" is the one in the up-pipe (pre-cat I assume). I asked my mechanic some questions as to which CC needed to be replaced and he said I was asking the same questions the Subaru dealer was asking (either when he was pricing the part so they knew which one was at fault and/or if he also called to find out exactly what was causing the CEL and how to repair it) so I know he was in contact with them. He also stated that it was the only CC that's being "monitored" and that's the only one I know that has any sensor near it (the EGT sensor).

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    Quote Originally Posted by MainFrame View Post
    The uppipe is labled "H" in this diagram:
    Thanks. That's what I was thinking. I assume "W" is the turbo? $349 part + shipping there. So yea, I guess it's probably gonna list out at $500-ish from my mechanic.

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    Uppipe cat is the only one which temperature is monitored, but the rear O2 sensor monitors the effectiveness of ALL catalytic converters on the car.

    The price of the part is completely irrelevant because you should NOT replace it with the same part. As has been stated several times, you need to install a catless uppipe instead of the factory unit.

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    Quote Originally Posted by MainFrame View Post
    The price of the part is completely irrelevant because you should NOT replace it with the same part. As has been stated several times, you need to install a catless uppipe instead of the factory unit.
    I wouldn't necessarily say I "need" to. It's ran fine for 9 years and 137000 miles w/no problem until now.

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    Quote Originally Posted by Obeisance View Post
    I have no guesses for you about the cat causing overheating, but I think I've heard before that the function of catalytic converters degrades quite a bit at higher temperatures
    That is entirely wrong and opposite of the truth. Catalytic converters function better and better the hotter they get.

    Quote Originally Posted by SD_GR View Post
    Are you sure it's the up pipe? Just checking to save headaches, not trying to be a pain.
    I'm wondering the same thing. I haven't seen anything in this thread that tells me that's the source of the problem other than the mechanic saying that's the problem. What's the specific code(s) from the ECU? And do you have anything else to share in terms of why the mechanic is saying that's the problem?

    Quote Originally Posted by dttruax View Post
    I wouldn't necessarily say I "need" to. It's ran fine for 9 years and 137000 miles w/no problem until now.
    You're entirely missing the point. Regardless of whether you've had a problem before, this is a well-known, frequent problem area that will most likely cause catastrophic damage if it does come apart. At the very least it will cause significant damage. Since there's no advantage to having that cat in place, which is a well-established fact since Subaru eliminated them, it would be smart for you to remove this potential problem at the same time.

    Or you can ignore the advice of a lot of guys that are experts in Subarus and do whatever you want. But I don't know or understand why on earth you would come to any forum to ask for advice and then blatantly ignore it.
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    Quote Originally Posted by dttruax View Post
    I wouldn't necessarily say I "need" to. It's ran fine for 9 years and 137000 miles w/no problem until now.
    To put what the others are tying to say in perspective:

    If/When the Cat in the UP fails:

    * Shrapnel is sent into a Turbine blade spinning 10,000+RPM.
    * The turbine is connected to the Impeller via a solid shaft, The only thing isolating the outgoing (exhaust) side of the turbo and the intake side of the turbo, is a bushing and a few seals.
    * The turbo shares your engines oil supply!
    * The turbo shares your engines water supply!
    * there are CC's downstream!

    So what happens is shrapnel flys into the turbine, causes it to eat itself, the bushing, the seals, unbalances the impeller, and sends a whole lot of metal chunks into your motor. When this happens it is no longer just a CC problem, its a replace my motor, turbo, other CC's, radiator, whole ball of **** problem. When the Turbo dies, it pukes a ton of oil into your downpipe rendering your other two CC's to the scrap bin. Its expensive, very expensive, especially if you don't do the work yourself. They are not trying to be a PITA, they are right. And to further reinforce the point, Subaru realized it was such a problem that they fixed it by not installing a CC in the uppipe beginning with the 2006 MY, and haven't done it since. Infact in their history, they only did it from 2002- 2005 MY.
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    Quote Originally Posted by dttruax View Post
    I wouldn't necessarily say I "need" to. It's ran fine for 9 years and 137000 miles w/no problem until now.


    I suppose you're right.. just like I don't "need" to eat, but if I don't chances are I will die, sooner or later.



    You say it's ran fine with the catted uppipe, but aren't you on here now complaining about problems with it? I don't understand why you (or anyone) would want to pay significantly more for a part that's proven to cause problems.

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    Apart from the advice everyone is giving that you need to change the uppipe, if I wanted to quickly see if the front catalytic converter temperature was causing the problem, I'd try the resistor fix while the stock uppipe was in place- by removing the sensor and replacing it with the resistor, then re-setting the CEL, if the CEL did not come back on I would be lead to believe that the problem was located.
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    Re: Catalytic converter overheating?

    When my cat clogged it made my turbo make a horrible clacking noise under boost.

    My dealership actually said something along the lines of "normal Subaru procedures in your case is to replace it with a catless unit".
    So even they were against the cat!

    Posted from a fone.

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    Catalytic converter overheating?

    When BOVs were not used, turbos would clank! loud as the pressure in the exhaust side interacted with the spinning parts. That's interesting.

    In order to legally use a catless up pipe in CA unless I amid taken one would have to switch to an intact 2,5L with all smog controls including the air pump, and rest according to the standards of the later year.

    In any case since Subaru does not to my knowledge have a CRL fix for the catless up pipe, the dealer would be taking a legal car and making it not just technically but also visibly illegal.

    I find that absurd to some extent but in this world anything is possible.
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    Quote Originally Posted by UEDan View Post
    When my cat clogged it made my turbo make a horrible clacking noise under boost.

    My dealership actually said something along the lines of "normal Subaru procedures in your case is to replace it with a catless unit".
    So even they were against the cat!

    Posted from a fone.
    Seriously...so much as in fact, they stopped using catted units at all when building the cars for the US in 2006, with the 2.5L engines (04, with the STIs technically).

    So why the hell would anyone spend MORE money to put a detrimental part BACK?

    So yeah, 9 years 100k+ miles until you had your FIRST problem with a cat...so why not replace it with a part that would guarantee you to go infinite years and infinite miles without having an issue due to that part? No-brainer to me...
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    Quote Originally Posted by Mikie13 View Post
    So yeah, 9 years 100k+ miles until you had your FIRST problem with a cat...so why not replace it with a significantly cheaper part that would guarantee you to go infinite years and infinite miles without having an issue due to that part? No-brainer to me...
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    Update: The CEL code was P0420 which is the catalytic converter below threshold code. So it wasn't a high ETG reading that sent the code and would mean (I think) that the oxygen sensor that's right by the mid-cat would have sent the code.

    Question: would this code mean that the pre-cat is going bad, or just the mid-cat?

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    the mid cat most likely...or a bad O2 sensor.


    You should still replace the UP.
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