so i've been playin the cat and mouse game trying to get my jeep right. it's had a loud hum/kinda vibration for a while now. ruled out tires and steering.(had an alignment, rotated, checked hubs/balljoints and rod ends. all good). moved on to driveshafts, took the front one out, drove it around, still there. greased the hell out of the rear ds(was quite dry) and feels to be driving ok but the hum is still there, much more so at certain speeds. i'm kinda thinking it may be my exhaust leaking or my cat going bad. i had thought it was a driveline problem b/c it's only apparent when on the throttle. in turn, the loud hum makes the jeep slightly sluggish at some speeds. replaced plugs about 2 weeks ago and still idles a little rough(feels rough at idle, cant hear anything rattling around in the cat when revving in N). and i'm sort of leaning away from driveline b/c i cant feel it as much as i can hear it. so, i guess the question is, could my exhaust be leaking that bad or the cat going bad as to where it sounds like a driveline problem and hinders performance of the jeep? i feel like i am rambling now as this post is quite long, tell me if this all makes sense or not. thanx for any help guys.

01 4.0L I6. stock motor, k&n drop in filter, rusty's flowmaster 40 exhaust.

 

I replaced my cat with a new Magnaflow converter last week. When I would start or shut off the Jeep, I could hear a loud rattle. Sometimes I could hear it rattle in traffic at idle. I assumed the heat shield was loose and decided to replace the cat. Once I got it off, I discovered that the rattle was something loose on the inside the converter.

When I installed the Magnaflow, I also swaped the factory muffler and tail pipe with a Dynomax Super Turbo cat back. It feels a little stronger than before...most likely due to the age of the old converter. For what its worth, mine had right at 178k miles when I finally changed the cat, but I have been told that they are usually done for by 80-100k miles.

 

im at 87k. it sometimes feels weird when i shut the jeep off, shakes a little.

 

Yep, mine made the most noise when I shut it off. It sounded like someone kicked over a metal trash can.

 

Humm from the tires? I know it may be a stupid question but I have to ask. I too have the rattling cat. I have seen a ton of cherokees with this problem. I plan on replacing my exhaust soon too since the bad head gasket poured water into the muffler creating a hole from rust. Good luck with the fix. If you plan on replacing it by an exhaust shop then I would buy your own cat. They charge you crazy money at the shops. Get a high flow one while your at it.

 

i'd ruled out tires simply for the fact that i only hear it when i give it gas.

ahenderl, mines not that bad when i shut it off. i hit it a few times when it was running and it didnt make any noises.

 

I don't think they always make noise when you hit them. I looked at one that didn't when I kicked it. Mine only rattles on start up. It would freek you out if you didn't know what it was. I thought it was the motor the first time I ever heard one.

 

any other way to figure out if its bad? i know my exhaust leaks, it always has. but it passed va state emissions a couple months back.

 

Other then taking it off, I have no clue.

 

so back to the original question, would the cat going bad or my exhaust leaking cause the vehicle to drive like crap? with a loss of pickup at certain speeds and somewhat of a rough idle. i havent heard any noise coming from the cat, but could this just be preliminary stages of it going bad? at certain speeds the loud hum almost sounds like my ds is wobbling or something, or i have crazy m/t's, but it stops when i let off the gas. and like i previously stated, i cant really feel a vibration as much as i can hear the loud hum.

 

i have an 88 laredo and without warning one day i completely lost power!!! and i mean completely... 2000 rpm's was all youd get out of her it took a 2 mile straight stretch to get up to 40 mph but when sitting it'd rev up just fine... then a couple weeks later im toolin around with it and thats when i heard the tell tale whine in the exhaust when reving it up. well i took off the cat and cut off the mufler (stockers by the way) and pounded out the cat. it was totaly full and took us 45 min. to clean out. what came out looked like ash colored petrified wood. then i cut the muffler in 2 and it was in the muffler too. put on new cat and a mildly used flowmaster from a buddy and now it sounds great and runs like a raped ape