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-   -   knocking/ rattling = bad catalytic converter ? advice please. (

nicholas.c 07-01-2013 01:57 PM

knocking/ rattling = bad catalytic converter ? advice please.
I have a 2004 wrangler X with a catalytic converter in need of replacement (the diagnostic code says so) and it has been that way for a couple weeks.

I was saving up to buy the part and then over the weekend it started making this hollow knocking noise.

it is present at idle and seems to dissipate significantly when I get up to 35 + mph. the noise does fluctuate with RPM change as well. not sure if it goes away up above a certain limit.. not wanting to push the engine too hard to find out.

oil level is good
spark plugs just changed
only diag code is for cat.


Is there an easy way to disconnect the catalytic converters to see if the noise goes away? I imagine the engine noise will be alot louder without them (and the muffler) in place.

just to add to the fun, my license plate has a July sticker and our county has required emissions testing.

Cape Fear Finn 07-01-2013 05:44 PM

Tap the cat with a screwdriver handle firmly. If it is the cat you might hear the rattle.

ChaddG 07-01-2013 07:51 PM

stupid emissions testings..... your going to want to have the cat. and muffler in place.
the cat. should come off fairly easily. few bolts after the exhaust headers and a few more to disconnect the pipe from behind the cat.
unclip any o2 sensors in the way of removal and re-install. blast all your bolts with some kind of anti-seize lubricant such as pb blaster a day before or two, and if you have any gaskets in the exhaust line, replace those too.
Previous owners may have not used replacement gaskets if they worked on it and had not brought it to a garage for the job to be done.

nicholas.c 07-01-2013 08:29 PM

I'll try and knock on the cats (both mini cats and the full sized ones) tonight. I might have an exhaust guy look at it tomorrow. can a bad catalytic converter actually damage the engine?

Jerry Bransford 07-01-2013 08:32 PM

The worst I can think of a cat can do is if it breaks up internally, it can block the exhaust gases and significantly (temporarily until it is replaced) reduce engine performance.

Jeepfixer1 07-01-2013 09:01 PM

If it breaks up and stops the flow enough I have seem the excess pressure blow out a rear main seal also can make the engine run hotter and even see the tips on spark plugs bend although these are more extreme cases. When they break up they sound like a golf ball size rock rattling in a can. You can very easily hit the converter with the palm of your hand and they will rattle. Just make sure the exhaust isn't hot. Also if you take your exhaust off it will be so loud that it'll be hard to tell if the rattle is there or not. If it is loud enough to hear over open exhaust then there's no way it's a converter to begin with.. You can get universal obd2 compliant converters for less than 100$ at oriellys and advance but you need to measure dimensions and although you can clamp it in welding is preferred. If you take it to a shop I'd expect around 250$ total

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