1990 xj runs like poo after warmup

[DetroitStyle]

A clogged Cat converter would give problems all the time.

He said his runs fine at a cold start up.

A clogged cat converter would always, at all temperatures restrict exhaust flow and cause the engine to run rough as you increase engine speed with more gas, more throttle. And depending on how bad the restriction is from a clogged Cat converter it might or might not run rough at idle.

A broken, internal honey comb, loose guts in a Cat converter would usually rattle as you give it gas, and would randomly bog down on acceleration as the guts rotated around into different positions, blocking and unblocking exhaust flow.

I missed the later down post where Kim mentioned having a new exhaust with no catalytic... so I guess that's not the issue this time.

However, when my catalytic converter was plugged on my Z28, it would behave exactly as listed. It would start up fine first thing in the morning and run great for about 5-10 minutes, then slowly but surely start bogging down, etc. It actually felt like the trans was slipping a bit.

I would shut it off, wait 15 minutes and it would run fine for a minute or two, then act up again. Let it cool down fully and it was fine for 10 minutes. Rinse and repeat.

Finally I cut a slot in front of the cat and it got a lot louder, but ran great again. Replaced it with an offroad pipe and all was good again.

 

[85xjwoody]

Little update. I have been busy working so I have not touched the jeep. I picked up an 88 cherokee yesterday as a parts jeep but runs great. So I am going to swap out some parts one at a time and see how that goes. I know, it isn't the best route to go, but it is what I got for now. At least I have a good running jeep that is pretty much the same to go off of. Lets see what the weekend produces. Thanks again to all who posted!! The help is much appreciated.

Kim

 

[Ecomike]

Quoting myself! "Check the dizzy to see if is pointing to number #1 plug at zero degrees, TDC on the compression stroke! But do the vacuum tests first! Google the test procedure. Vac gauge is cheap, and tells a lot of info on the engine!!!"

http://tidentenn.com/pdf/the-vacuum-guage.pdf

http://www.fordf150.net/howto/diagnoseengine.php

http://www.youfixcars.com/engine-vacuum-tests.html

Cheapest most useful tool you can ever buy!!!!

http://findarticles.com/p/articles/mi_qa3828/is_200108/ai_n8978956/