so since i bought my xj a year ago every once in a while when i start it when the engine is warm it will shudder and shake like crazy and the exhaust system will shake so bad it feels like its ready to fall off. As soon as i get the RPM's up the shaking will stop and everything will be fine again. I'm pretty sure the problem is that my cat is on its way out because my gas mileage has gotten REALLLY bad too.
I thought it was a misfire at first but the engine is throwin out any codes indicating that so i'm left to assume that its the cat.
So before i go replacing that does anyone have any input? I just wanna make sure before i throw money at it and find out that it wasnt the cat that was the problem.

thanks in advance.

Jesse J.

 

Climb under and tap on it, see if you hear any rattling from inside to indicate it's broken.

If it's clogged good it would appear hot as well.

 

It's a long thread to read through, but you might find some helpful info in it.

https://www.cherokeeforum.com/f2/bad-mpg-99-xj-28434/

 

that was a helpful read for sure but it the difference with mine is the entire exhaust shakes like crazy and it sounds like it choking tryin to get the fumes out.. thats why i'm pretty sure mine is the cat

 

take the upstream O2 sensor out, if it is the Cat, this should provide enough flow to allow it to run like normal, therefore verifying that it is the catalytic converter that is clogged...

 

Search "heat soak" , my 2000 does the same thing. There was a factory TSB.

 

just read that but my check engine light doesn't come on? my symptoms are similar but not identical... but what i did notice was someone posted that there exhaust tip was really black and mine is too.. so that tells me its running rich but to me the heat soak thing doesnt explain the exhaust system shaking like mad..

 

My XJ will run like crap with a very crappy idle and if I let it continue like that it would run rich. Mine will usually smooth out quickly as I drive.. I suppose if your exhaust is loose it could shake like that. Also, I wasn't aware that "heat soak" conditions caused the CEL to light up, might doesn't, anyways.

 

k so i wanna check out that heat soak deal but i'm 18 and am not really familiar with the whole TSB routine.. so do i just take it to the stealership and ask em to check it out or what?

 

Take the cat out and see if it still does it.

 

check for leaks too in the rest of the exhaust too. you could have some build up in the system, maybe try running some seafoam through your TB.

 

We're both Canadian. Seafoam must be some controlled substance here.
Have never seen it at any of my trips to the Parts source (same as your auto zone).

 

 

just do as stated above.. Remove your o2 sensor and start it up.. it will alow it to breath if its clogged.. If the sensor is to hard to remove just drill a 1/2 inch hole to let it breath and weld it up after you find out what your prob is

 

You're right it is a controlled substance but me and my buddy were in napa the other day and they have it! I'm plannin on buying some just to clean out the systems.