Rednroll

As suggested a code reader is your best bet so you at least have some kind of insight of the trouble you might be getting yourself into. I would suggest investing a little more in the code reader and get one that can read ABS codes. The standard Android apps including the widely used Torque Pro app can only read stored ECM codes. Things like wheel speed sensors and any ABS module related problems won't show up on those ECM only code readers.

Based on the symptoms, I'm going to guess it might be O2 or Catalytic converter related if those haven't been replaced yet at 200K miles.

mr72

Yes, catalytic converter, that's the first thing I suggested.

No on the O2 sensor. Everyone wants bad catalytic converter to actually be JUST the O2 sensor. But an O2 sensor will never cause this symptom, even if you completely unplug it. Go try it, you'll see. If the voltage coming from the O2 sensor is outside the expected range, the ECU will just ignore it and run in open loop, light up the CEL and post a P0420 or whatever. You'll get marginally worse gas mileage and maybe a blacker than normal exhaust outlet.

engine not revving over 3K while under load is a result of a severe mechanical restriction. It could be purely wear induced, like either a bulk airflow restriction (plugged exhaust, intake), some airflow not working right (bent valve, HUGE valve clearances, jumped time/mistimed cams, shot rings), OR it could be electronically induced, LIMP mode engaged, due to some sensor-read condition that the ECU is programmed to think means the engine is at risk if it revs above a certain level, so you need to just drive it to the shop and open your wallet.

There are sensors that would fail and cause limp mode, but not the O2 sensor. MAF would do it, TPS would do it, CAS or CPS might do it, if the engine would start at all. On a VVT engine this is very common with the VVT actuator or VVT oil pressure switch, dunno if the 3.8 does this. 3.6 probably would.

karls10jk

These jeeps do not have a mass air flow sensor, only intake temp and manifold absolute pressure.

mr72

Thanks for that. Then instead of MAF, replace what I said with MAP. different method to do the same thing.

And if the MAP sensor is hosed, disconnected, etc. then it will likely result in "limp" mode if the Jeep starts at all.