90 4.0L No power, no rev past 1400 rpm

[90cherokee]

Ok, I am a newbie to the board and I would like some help.
My Jeep has never had much power, but this is getting ridiculous.
I have put in new plugs/wires/cap/rotor/coil. Checked for vacuum leaks. No check engine light. Starts and idles fine. Just will not rev up or have any power at all. Undriveable. Cat converter should be fine, new within 3 years. Is there a good way to check for intake/ehaust manifold leak?
Could it be timing related or throttle position sensor?
I came out to start it and drive this morning, and it just wouldnt go.
Please help soon, the snow is about to fly again.
Scotty I need more power!

[EquityDog]

I had very similar symptoms in an old International Scout and it turned out to be an internally collapsed muffler. The baffles had come loose and moved around to where they blocked most of the flow of exhaust. It was open enough to pass the low volumes emitted at low revs (idle) or even fairly high revs without load, but when you tried to drive, there was no power. I had gone through all the usual things you have tried without getting the power back. By chance I had disconnected the exhaust pipe after the down pipe and was moving the car (huge racket, of course) when I found the power was back.

This may not be your problem, of course, but it's a possibility. The muffler looked perfect from the outside so it's hard to diagnose for a backyard mechanic.

[comp]

yep i've seen pipe do it also, it was dub. wall pipe , inside went
converter and 3 yrs? i'd still check, if you have a vac. gauge connect
it to manifold vac. if good at idle, raise RPM to about 2-2500 and watch
and see if vac. gauge starts to fall, it's a rough test,but a good indicator
of clogged ex. sys. you just don't know where

[90cherokee]

It was the cat converter. I replaced a somewhat leaky injector ( the small cup in the fuel rail was bad..not the seal on the injector) and took the pipe off. What a glorious sound....a great roar, lots of smoke and free revs.
Thanks for your advice!!

[comp]

cool REVVV on be don't get a ticket

[MagicRat]

Good news!!
Just correct the problem that made your 3 year old cat go bad in the first place.

Sometimes if the engine runs too rich, it can overheat the converter allowing the ceramic stuff inside to melt into a blob which cuts off flow.