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Help: catalytic converter and CEL question

Discussion in '1st Gen. Tacomas (1995-2004)' started by pt law, Dec 10, 2011.

  1. Dec 10, 2011 at 5:05 PM
    #1
    pt law

    pt law [OP] Well-Known Member

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    Steve
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    gray wire mod...soon
    I replaced my exhaust cat back with a factory replacement and new gasket at the union due to a hole in the muffler. A week later my truck threw a CEL for catalytic converter inefficiency (I was stupid and did not remember to get the specific code). I had it cleared and ran it for another five days only for the CEL to come back on. I have not run the code yet (I do not have a scanguage) but will bet it is the same code.

    What is causing this? The hole in the muffler developed over time and I left it like that for a month before finding a factory used exhaust. Would the computer get accustomed to the hole in the muffler, causing the computer to now think that the added compression in the exhaust is a problem compared to the hole that was there for a month?

    Should I clear the code, disconnect the negative battery terminal and let it sit for 15 minutes, and then see if it comes back?

    Will I damage the cat if I drive on it with this code?

    I have a hard time believing my cat died a week after replacing the exhaust. 95K on the cat.

    Thanks!
     
  2. Dec 10, 2011 at 8:13 PM
    #2
    pt law

    pt law [OP] Well-Known Member

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    bump...
     
  3. Dec 10, 2011 at 8:48 PM
    #3
    rll131

    rll131 rll131

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    To my knowledge I whole in the muffler won't throw a cat code the exhaust leak would have to be upstream from the cat. You probably have a bad cat or u2 sensor.
     
  4. Dec 10, 2011 at 8:56 PM
    #4
    pt law

    pt law [OP] Well-Known Member

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    Downstream 02 sensor was just replaced in the last year and is Toyota OEM part. CEL is not reporting an 02 sensor code.
    Its just seems to coincidental to throw a code within 5 days after the new exhaust install. The cat literally would have to have developed problems/die within those 5 days.
    I am not saying the hole in the muffler caused the code. I am wondering if the computer could get used to the lower resistance in the cat due to a hole in the muffler for a month and now that the resistance is higher (air has to travel all the way through the exhaust rather then pouring out the muffler), it is throwing the computer off :confused:
     
  5. Dec 11, 2011 at 9:40 AM
    #5
    pt law

    pt law [OP] Well-Known Member

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    gray wire mod...soon
    next day bump...anyone?
     
  6. Dec 11, 2011 at 9:53 AM
    #6
    joes06tacoma

    joes06tacoma Well-Known Member

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    It's my understanding that the ECU just compares the two 02 sensor readings and looks for a difference between the two to determine the CAT is working.

    Since vehicle problems that occur right after a modification or repair are frequently linked to whatever you just did, I would be checking any wiring harnesses in the area you were working in. Maybe a pin backed out partially inside the 02 sensor connector? Pinched or cut wire? Seems like a leak at either gasket at the CAT could cause an issue too, since it would provide another place for the 02 to exit without running over both sensors and through the CAT.

    If the engine is running correctly, I doubt you hurt the CAT. I have ruined one before by running the engine 1K miles with a slight miss (idled rough). The unburned HCs killed it.

    Try not to throw money at it buying parts. The CAT can be checked at a shop that has a gas analyzer by sniffing the exhaust before and after the CAT. The 02 sensors can be checked with a scanner if you can get access to one. You can actually watch the sensor readings in real time. A bad one will usually just stay in one position and not change. High school auto shop is a long way in the past now, but if I remember right you can check an O2 sensor with a voltmeter. Should be 0-1 VDC and should "cross count" back and forth with .5 volts being the midpoint. Might be worth a shot before paying out the nose for a diagnostic. I know it is hard to get someone to diagnose a problem like this with out shotgunning parts at it.
     
  7. Dec 11, 2011 at 5:15 PM
    #7
    pt law

    pt law [OP] Well-Known Member

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    gray wire mod...soon
    Thanks! Great advice and makes sense. May be the seal at the gasket at the rear of the cat has a small leak.
     
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