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Thread: What are the symptoms of a bad cat. conv.

  1. #1
    Senior Moderator Larry's Avatar
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    Default What are the symptoms of a bad cat. conv.

    Getting on the interstate today the heep just nosed over. Runs really rough, and at idle seems to have very high exhaust pressure at the tailpipe, as compared to my wifes XJ. Injectors checked out OK, and I replaced the plugs, cap rotor and plug wires. 98 TJ, 125,000 miles.

    So, the question is: what are the symptoms of a bad catylic convertor?

    The search yielded some info that essentially indicates they don't fail

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    Registered JeremyH's Avatar
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    Well......most catalytic converters have a huge chunk of (I blieve) porcelin in them......and the usual reason for them failing is that piece of procelin breaking and one of those pieces cloggin up the output...which would block the exhaust and cause a loss in power. Symptoms of a bad cat....I'd say the rattling of that broken chunk of poercelin......but just because you dont hear a rattle doesnt mean it didnt break off.

    As for them not failing....that is not true.....I have figured out that wheeling a vehicle causes them to fail faster (beating around a percelin piece not good).

    However since you say that there is an abnormally high amount of exhaust coming from the pipe....then I'd say that your cat is not bad.

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    I have to laugh some times when going down the highway and some car passes by with the cat glowing red hot. can u imagine how plugged it must be to do that? as for trying to figure out if the cat is bad, other than hearing an obvious restiction in the exhast, the glowing indicator, the rattle indicating a broken brick, you may just have to pull the muffler off and look up into it. the cat can also go bad by just melting due to too rich of a mixture causing it to get too hot, or by fouling. pulling the muffler for a visual inspection is probably not fun but you should be able to determine the condition by judging if it looks good or bad. given your milage, it may be time. as a bonus to pulling the muffler, and you find it chunked or melted, at that point you could smash the innards and pull them out to hollow out the cat to get by until you replace it with a new one, of coarse, that should only be a temp solution and may be unlawful emmisions wise depending on the state.
    2000 TJ Sport HP 9" spooled rear,Warn hub conversion, 33" swampers, RK 5.5 springs front, Currie 4" springs rear, Currie rear bump stops, front Lock Right

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    Senior Moderator Larry's Avatar
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    Yeah, it's not the cat. I just pulled the new plugs and they are black as night. Gotta be an ignition problem of some kind. Diagnosing engine problems was sure a lot easier 25 years ago

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    In case anyone else is wondering about symptoms of a plugged cat -- low vacuum, decrease in power, poor braking due to lack of vacuum assist.
    Joel

    '97 TJ 5.7 Hemi, 545RFE, Iron Y front long arms, WJ cross over steering & brakes, F&R Truetracs, 4.56s, 8.8, 2 1/2" OME, 295/75R-16 BFG ATs, HS9500i, TummyTuck.
    '07 Commander Overland

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    Senior Moderator Larry's Avatar
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    -=- originally posted by Joel -=-
    In case anyone else is wondering about symptoms of a plugged cat -- low vacuum, decrease in power, poor braking due to lack of vacuum assist.
    Well, then maybe I do have a plugged cat. Manifold vacuum at idle rapidly fluctuates between 7 & 12 inches, and doesn't drop much at 1500 rpm. hmmm

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    Icon312 bad cat

    Hi,
    I had similar trouble with my 98TJ. Turned out the oxygen sensor was bad. It caused loss of power and rough idle.
    98 TJ
    00 Tahoe Z71

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    -=- originally posted by Unionguy -=-
    Well, then maybe I do have a plugged cat. Manifold vacuum at idle rapidly fluctuates between 7 & 12 inches, and doesn't drop much at 1500 rpm. hmmm
    I thought fluctuating vacuum meant you had a leak. At least that's what it says on my vacuum meter instructions.
    RED 92 YJ - Cobra CB, OBA, KC Daylighters, GPSIII+, 4 banger, 31-10.50 GY / MT,WARN X8000i.

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    Senior Moderator Larry's Avatar
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    Here's the diagnosis:

    Broken 3# intake valve spring. Hopefully nothing else got taken out at the same time.

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    i had the same type of problems about a month ago...lost braking and power..it ended up that i had a leak in the vacum hose behind my air box...got a new hose and problem was fixed...just another thing to check i guess

    brs:gulpbeer:
    2003 TJ bright silver metalic...and some stuff attached to it

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    my cat did break and rattle.
    my O2 sensor also went bad.:sousy: (check engine light clued me in)

    it ran like crap. felt like it was running out of gas or had bananas in the tailpipe.

    i replaced the cat with a hi-flow one from
    xtremeflow.com
    i also put in a high flow muffler and 2.5inch tailpipe. (magnaflow)

    it runs A LOT BETTER :spinhead:now and my jeep sounds a lot deeper and it feels like it has more power so now i'm saving my nickels and dimes
    for a banks header and torque tube.
    red97TJ Rancho 2.5lift +coil spacers, RS9000's
    33x12.5 All Terrain Yokos
    IPF Headlights,Cheapie JCW lights, Hella 500 fogs

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