I'm getting 2 codes on my 2000 XJ 4.0L. 1. P0171 2. Fuel System too lean. I know its burning rich. So too lean doesn't make sense. When I try to drive the Jeep it has a loss of power and at lower rpms it sputters and shakes alot. I'll give it throttle and it acts like it's being bogged down really bad and then all of a sudden it will take off. Once I reach whatever speed I want to travel and let off the throttle and rpms drop as it shifts into overdrive it goes right back to spitting and sputtering around quite violently. Anybody know what this could be?

 

Sounds like an O2 sensor. It thinks you are too lean, so it's dumping gas in to compensate.

OR, you have a vacuum leak ahead of the sensor, so it's seeing a lean condition.

O2 sensors, like most sensors on these beasts, are very picky. Do NOT buy an aftermarket sensor. Get NTK/NGK parts only.

BTW, you'll have a lot easier time changing that sensor if you apply some serious heat around the sensor first. A propane or MAPP gas torch works well. OR, you can drive around for a half hour then change it.

Can't hurt to verify fuel pressure before you drop the money on O2 sensors. You can probably rent one for free at Autozone.