Loss of power at WOT

[sam24th]

Ok so Ive got a new problem with my jeep. Its not really bogging, its more of a loss of power at WOT. The engine wont go above 3000RPM even with the peddle floored. I used to be able to floor it and it would almost redline and run beautifully. I also want to note that in park and neutral it revs up just fine.

Some background info:
Year: 1990
Engine: 4.0
Trans: AW4 4WD with NP231

Things checked and already ruled out.
-fuel pump
-pressure regulator
-fuel filter
-sparkplugs, cap, rotor and plugs
-tps
-cps

I also want to note the jeep was running perfectly fine before I tore up my yoke and dropped the driveshaft going down the highway. I replaced the yoke and the driveshaft and now my jeep has a major loss of power. It also only does this while in gear. In neutral or park I can rev it as high as I want and it sounds fine. Any thoughts?

 

[JJacobs]

Plugged cat? Loosen the downpipe or take out the o2 sensor and see if it'll rev out.

 

[gradon]

That's what I'm thinking. Did the driveshaft get to whack the underbody?

 

[CharlesS]

Several ways to troubleshoot an obstructed CAT:

The easiest test for converter plugging is done with a vacuum gauge. Connect the gauge to a source of intake vacuum on the intake manifold, carburetor or throttle body. Note the reading at idle, then raise and hold engine speed at 2,500. The needle will drop when you first open the throttle, but should then rise and stabilize. If the vacuum reading starts to drop, pressure may be backing up in the exhaust system.
You can also try to measure backpressure directly. If your engine has air injection, disconnect the check valve from the distribution manifold, and connect a low pressure gauge. Or, remove the oxygen sensor and take your reading at its hole in the manifold or headpipe. Refer to the backpressure specs for the application. Generally speaking, more than 1.25 psi of backpressure at idle, or more than 3 psi at 2,000 rpm tells you there's an exhaust restriction.
If there appears to be an exhaust restriction, disconnect the exhaust pipe just aft of the converter to relieve pressure and recheck the readings. CAUTION: The pipes will be hot so wait awhile for things to cool down. If vacuum goes up and/or backpressure drops, the problem isn't not a plugged converter but a plugged muffler or collapsed pipe. If there's little or no change in readings, the converter is plugged.
Just because a converter is passing gas doesn't mean it is okay. If the catalyst inside is contaminated or worn out, high carbon monoxide (CO) and/or hydrocarbon (HC) readings will be present in the exhaust. If you have access to a high temperature digital pyrometer (or an oven thermometer will do), check the converter's temperature fore and aft. A good converter will usually run 100 degrees F hotter at its outlet than its inlet. Little or no temperature change would indicate low efficiency, or a problem with the converter's air supply. Converters need supplemental oxygen in the exhaust to reburn pollutants, so if the air injection system or aspirator valve isn't doing its job the converter can't do its job either.

 

[sam24th]

I did a visual inspection of the underbody of the jeep before installing the new yoke and driveshaft. It looked alright although it did give the rear part of the trans tunnel a bit of a whack. I didnt really think to check to see if its a plugged cat. I'll check it tomorrow and see whats up.