Loss of power/acceleration after new catback and manifold? Clogged Cat?


New Member
Nov 1, 2021
San Antonio Texas
Hey all! Thanks in advance for all the help as always!

1998 4.0 manual transmission with 96k

So here’s the scoop!

For about the past 9 months my TJ has had an exhaust leak. First was the flange. Tightened that up and it helped. Slowly got loud again but not crazy loud. Finally this past Sunday I changed the exhaust manifold/header. Sure enough it was cracked around some of the welds. Put in new manifold and everything was fine.

A few days later, Wednesday I change my stock muffler and tailpipe as there was a hole in the muffler that seemed to be getting worse especially after the new manifold. After getting everything tight and some permatex to stop small leaks near the clamps I drove the Jeep about 80-90 miles round trip out in the hill country. It drives nice and smooth now but..

I noticed going up some hills I frequent, that at around 50+ mph the Jeep seemed to be more sluggish than normal. I even once had to downshift to 3rd to get up a bigger hill and somewhat maintain speed. And in 4th and 5th going up hills I’m flooring it and it’s still hardly maintaining or slowly decreasing speed.

Also it seems to take longer to accelerate now. As in I can floor it in 3rd and 4th gear for quite some time before shifting. (When getting to highway speeds.)

When I changed the muffler I did leave the muffler off for a night and put a towel over the outlet so bugs or critters wouldn’t try an get in.

My questions are, could there be something up with my cat? Jeep Seemed fine after manifold and before the cat back went in. No codes or anything still.

Is this just a symptom of all the changes in exhaust? Maybe this is how Jeep TJ is supposed to run but I’ve gotten used to an exhaust leaky Jeep?

ALSO my mpg have not tanked. If anything seem much better strangely enough.

Am I crazy?

Could I have messed up the cat by leaving the towel on it?

Could it be clogged? Contaminant’s?

And Jeep is NOT overheating. If anything it’s running cool! Used to be if I was at idle with the AC on I would be right at 210 maybe a hair over now it won’t even hit 210.

I don’t have a temp gun to check the inlet an outlet. Plan to soon.

I’m stumped and hoping that I’m just crazy!

Thanks y’all!

(Also pipes seem to be getting oddly hot? Maybe I just never noticed on stock but these stainless pipes are already changing colors like crazy and they sizzle off bits of water in an instant)

Thanks so much!