4.0l power loss, decrease in mileage, black smoke/soot

[parabs]

Over the last couple weeks, I developed what seemed like intermittent power loss, and last night it was confirmed.  I drove 800kms, stopped for about 2 hrs, then came from med hat to calgary ~280kms. 

I couldnt go over 110 in top gear, I had to press on the pedal to maintain speed going down hills, ie the hill by Gleichen (sp?) and I burnt 60l in a trip that I usually burn much less.

Im going to change out the plugs, im not getting the check engine light, and I checked the codes with my own personal reader and got nothing.

Maybe O2 sensor?

Your thoughts?

Thx in advance.

[Justink]

Map sensor? That caused me to blow black smoke and I had a major power gain when  I replaced it.

[parabs]

I changed the plugs, no noticeable change.

I read on jeepforum.com, and then I disconnected the upstream o2 sensor, and it is working pretty good now, so I am going to change it out tomorrow.

If the problem recurs, I will have to look deeper into the map sensor..

[Krisman]

im not sure what kind of scanners autovalue has, but maybe give that a shot. they let you use them for free i believe.  the snapon ones will show you voltages, you can check o2 cycle voltage

[hps4evr]

catalytic converter could be starting to plug up. try the O2 sensor, then try cat con.

[parabs]

turns out it doesnt seem to be the O2 sensor.  I changed out the TPS and now it is running much better...but I wont know if it is fixed until I run a couple tanks through it..

I didnt think of the cats Eric, do you know if you gut/cut out a cat will the computer throw codes??

[hps4evr]

it could throw a code as the downstream O2 isnt getting the reading it should. but ive seen some that didnt really care after the cat was removed. so it may be worth a shot.

[WagoneerXJ]

there are ways to fool that downstream O2 sensor. cheap too........ I have the one on my gf's TJ fooled for months now