Reilly xj

So when I had my new engine put in (still 4.0) I couldn't get my jeep over 70mph, turns out my cat was clogged so since the shop knew I spent already 4000 they just put in one-size-fits-all cat, then I can get in the 70s but flooring it up hills on the hwy to stay there, I feel like I'm dragging an anchor behind me.....my thought is that the cat isn't letting enough airflow through.

I have 5,000 on the engine now and actually went from 31s(when I noticed the problem) to 32s and the problem isn't worse so I can't blame it on gears. And I've kept up with tune ups as well so that's not the problem

I'm thinking of doing a high flow cat so before I go to the muffler shop and pay all that money does anybody have any ideas or thoughts on the problem

Reilly xj

97 jeep xj 4.0

fb97xj1

You really should find out why the old cat was clogged, or the new cat may suffer the same. A cat will clog when it overheats too often. This can be caused by running too rich, or passing coolant. Even oil. The substrate inside goes into meltdown, literally. Your o2 sensors may be fouled at that point so consider replacing them as well (they may have caused the meltwown in the irst place, who knows). Check your fuel pressure and for any vacuum leaks. And check for any pending trouble codes that may have attributed to the cat going out on you. It clogged for a reason. Replacing it is only part of it.

Reilly xj

All o2 sensors are new and no leaks at all surprisingly. The sluggish on the the hwy happened right when the old engine blew then cat got replaced with new engine and 02s and it got better but not as good as I want. And I think trying a high flow cat(witch I already want anyway) would be an easy less expensive way to test theory's

BillyBoy

A Detroit jeeper would unhook the exhaust... run it... check your theory. ? Might be loud for a minute.

Radi

Flooring it up hills at 70 MPH with 31"- 32" tires sounds about right to me. Unhook the cat for a short drive and see if it makes any difference.

dans98xj

I'm with Radi on this one since you went up in tire size the gearing on it now is crap. with 31's you should be at 4.11's to get back to stock. With the 32's you will be more in the 4.56 range. Were are you located? If you are in the mountains like 4,000 feet and up the jeep is going to be getting choked out from lack of oxygen too that will make it a lot harder to get to 70.

Bustedback

32's with 3.55 gears makes for a sluggish turd in the hills.

Fred/N0AZZ

^ What he said ^ not much doubt.

JeremyXJ

I've got 32's with 3.55's. Definitely slowed it down and hurt my braking. I manually put it in third when going uphill on the highway.

EZEARL

Do the rear disc conversion.