I have a 90 xj with the 4.0 that will not rev over 2 grand its a manual and has stumped everyone I know including the diagnostics machine any clue as to whats going on?

 

I had a GMC Sonoma that I couldnt rev very high when the catalytic converter got clogged.

 

yeah check just normal stuff like restrictions in the intake/exhaust.

 

listen for a whistle from the tail pipe.. if there is on clogged cat

 

had the same issue on my room mate's '87 renix 4.0.

replaced EVERY sensor on the truck, engine wiring, all computers, he has no cat and no muffler (straight piped), and no restrictions on intake. replaced fuel pump, fuel pressure regulator, and injectors, too.

last thing is timing. screw it. oh, and distributor is indexed to TDC#1 it runs, that's all he needs...

 

Some basic vacuum testing is very efficient way of determining if
you have a clogged catalytic converter.

Have you performed fuel pressure testing (pressure and volume) yet? With a gauge is the only way.
Probably should be ruled in or out.