No Codes Severe Power Loss

New to the group, been lurking a while and was told to see what the people have to offer, hoping someone has a direction for me to look.

2004 TJ Unlimited 4.0 Automatic. I’ve had it for about 2 months, the first couple thousand miles were great. Now I have a problem that is tricky to troubleshoot as I’m getting no lights and no trouble codes.

Seems to be a heat related problem but not overheating. If I jump in the jeep and take off, I get 3-4 miles and it starts losing power and rpm’s, if I keep trying to go it will gradually get all the way down to stalling. Still no codes or lights. Now if I cold start it and let it set in the driveway and idle for 15 minutes then take off, I only get about 100 yards before it starts doing the same thing. I have been throwing parts and getting tired of that.

New fuel pump and screen, new throttle position sensor, new crank sensor, new NGK plugs, and new NGK coil rail. New Wrangler Fix PCM, all of these parts have been added since the problem started and none have made it better or worse. Anyone been down this road?

Thank you

you have a bad cat ! My 06 acted the same way when one of the upper cats honeycomb came lose. No codes just no power. You can remove your upper o2 sensors but be warned, I melted my wire looming and clutch master cylinder line doing it but it did cause me to figure out it was the cats !