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Symptoms of a bad catalytic converter?

This is a discussion on Symptoms of a bad catalytic converter? within the Technical / Maintenance forums, part of the General Discussion category; Sometimes while driving around, my truck has absolutely no power, until around 2500RPM. It feels like the engine is bogging, ...

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    Registered User Ward83's Avatar
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    Symptoms of a bad catalytic converter?


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    Sometimes while driving around, my truck has absolutely no power, until around 2500RPM. It feels like the engine is bogging, and just refuses to rev. The engine is a '95 350TBI. The catalytic converter makes a rattling noise at idle, when the truck vibrates. I don't get a check engine light at all. Could the cat be plugged? Any other ideas?
    Last edited by Ward83; 07-16-2007 at 09:18 PM.
    1995 Silverado Ext Cab Stepside 5.7L
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    Re: Symptoms of a bad catalytic converter?

    No power is defenetly a sign of a plugged cat. A lot of times you can check for a plugged cat by measuring temperature at the cat. If it's plugged it's going to get real hot, and sometimes it will even glow bright red after driving for a while if it's plugged enough. You can also do a vacuum check to verify a plugged exhaust. I think if you got a plugged exhaust and you check manifold vacuum your supposed to see a steady drop to zero, i've never succesfully seen this happen so I don't know if you are supposed to give it a little gas and hold it and see if the vacuum starts drifting down or if it's just supposed to do it at idle. Usually exhaust shops that do catylitic converter replacement know how to check with a temperature gun to see if you got a plugged cat. That wouldn't be a bad place to start.
    Usually when you hear a rattling noise from the cat it's a good sign that it is coming apart.

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    Master Certified Tech performabuilt2's Avatar
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    Re: Symptoms of a bad catalytic converter?

    Usually when you hear a rattling noise from the cat it's a good sign that it is coming apart.[/QUOTE]
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    You feel lucky......Punk? RnuovZ71's Avatar
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    Re: Symptoms of a bad catalytic converter?

    Get under your truck And nock on the cat like you would a door. If its a dead thunk sound then its plugged. If it sounds hollow its fine.

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    Magician 95and96's Avatar
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    Re: Symptoms of a bad catalytic converter?

    When mine was bad it still had a hollow sound to it when I hit it, but also made a rattling sound inside. The stuff inside had broken loose and was turned sideways. The engine temp runs 10 degrees cooler now that the problem is fixed.



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    Re: Symptoms of a bad catalytic converter?

    When the cat got plugged in my GP, it had no power, especially above 4000 rpm. It also threw lots of random misfire codes.
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    Registered User Ward83's Avatar
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    Re: Symptoms of a bad catalytic converter?

    Well, the cat is definitely bad. Driving home from work today I could barely maintain 40mph, and it was taking like 2 blocks just to get it going that fast. Needless to say, I wasn't happy by the time I got home. After the truck cooled off, I unbolted the exhaust from the back of the cat, and pushed a long tire iron into the cat, and proceeded to bash the living hell out of the ceramic inside it. I could feel a big chunk of it loose near the back, which I assume was the problem. After crunching it up as much as I could, I started the truck and hammered the throttle a couple of times, and the cat puked alot of it's guts out the back. After bolting the exhaust back to the cat, I test drove it around, and it seems normal again. Hopefully this will last until this weekend, when I can get the cat replaced.
    Last edited by Ward83; 07-17-2007 at 08:57 PM.
    1995 Silverado Ext Cab Stepside 5.7L
    1988 Trans Am GTA 5.0L, 5-speed, 9-Bolt, digi-dash, leather

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    OBS Wingnut Drisco Z71's Avatar
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    Re: Symptoms of a bad catalytic converter?

    Quote Originally Posted by Ward83
    Well, the cat is definitely bad. Driving home from work today I could barely maintain 40mph, and it was taking like 2 blocks just to get it going that fast. Needless to say, I wasn't happy by the time I got home. After the truck cooled off, I unbolted the exhaust from the back of the cat, and pushed a long tire iron into the cat, and proceeded to bash the living hell out of the ceramic inside it. I could feel a big chunk of it loose near the back, which I assume was the problem. After crunching it up as much as I could, I started the truck and hammered the throttle a couple of times, and the cat puked alot of it's guts out the back. After bolting the exhaust back to the cat, I test drove it around, and it seems normal again. Hopefully this will last until this weekend, when I can get the cat replaced.
    hehe, i did the exact same thing when mine were plugged!

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