I have a 91 XJ I6. I recently had a tranny leak from a bad quick disconnect. I replaced the connection, replaced the tranny pan gasket while i was at it, and refilled the transmission fluid to the correct level. The leak is fixed, but the car now shakes a lot more than normal at idle and about 35ish. I checked under the car, and the cat, exhaust, and i believe the transfer case were all shaking more than they ever have. Some other things to note is that the cat has a glowing red ring at one end and i think i heard the tranny fluid boiling inside of the fill tube. Also when the leak happened, tranny fluid spilled all over the exhaust system, and there is a burnt marshmallow smell.

My best guess is that some fluid got into the cat and has clogged it, causing it to overheat/shake, but im stumped so far. Im going to take and in depth look to later to see if the cat is bad, if theres a bad hanger, or anything else. And i can send pictures if needed. Anyways, thanks for any insight you might have, cheers.

 

So, I actually figured it out. The cat seems to be good still, as i did the mallet test and it seems to be all in one piece. I took a look at the spark plugs and they all looked like this:

I cleaned them out and fired it up again. Much less shaking. I drove it around some and the shaking/ possibly overheating cat issue seems to be gone. So I figured it out, maybe this can be useful to somebody.

 

The catalyst probably was damaged by the failed ignition. Rich running no doubt. When the cat glows red, it was damaged, how much is not known.

So what caused the plugs to foul so bad?

 

Lets hope the cat keeps going a few more years.

I replaced the spark-plugs a few years ago, but maybe the build-up is because of the excess oil that gets into the combustion chamber? Its got 317,000 miles on it, so it burns a ton of oil.

 

Thats a lot of miles! The oil burning also harms cat. for now frequent spark plug changes will help. take a peek at a plug or two after 1000 miles to assess if they need cleaning or replacement early.

unless you need a smog test dont install a new cat with that oil burning. to prevent reoccurance of a red hot cat, perhaps a test pipe can be temporarily be installed in its place. red hot can mean fire hazard so avoid parking over flammables.

good luck
PS I got 305 K miles on mine, stock tranny but motor was rebuilt

 

Will do, thanks for the advice.