Ok guys i have 04 wj with the 4.0. Its been throwing p0174 bank 2 lean. I have replaced o2 sensors. Coil pack and plugs. Rear 3 plugs were covered heavy in carbon while the front 3 looked good. I dont know what to change now. Im getting about 9mpg and looks like a cummins when i start it up and give it some gas. I have spent hours searching for an answer. Please help!!!

 

Sounds like problem with air/fuel mixture. I would start by cleaning mass air flow sensor. Cheap and easy just need can of mass air flow cleaner. Maybe also make sure your air filter isn't extremely dirty and need changing. after that check the fuel pressure at the fuel rail. Autozone rents out a gauge for free to test the fuel pressure. Believe it should be at 50 psi for your car. This will rule out faulty fuel pump, fuel pump regulator, or clogged fuel supply line I believe.

These are other causes of the problem I found listed on other forums:
Restricted fuel supply line
Fuel pump strainer cloged
Fuel pump
Fuel pump regulator
Fuel filter
O2 sensor
O2 signal circuit
O2 return circuit
O2 sensor heater operation
MAP sensor operation
ECT sensor operation
PCM

I don't know much about last three on list maybe others could chime in.

 

Wow thats alot of possibilities. Ill start where you stated with the maf. Where exactly is the maf located? Which sensor is it on the throttle body?

 

There is not a MAF sensor on your WJ, you have a MAP sensor on the side of the throttle body. Check the exhaust manifold for cracks.

 

Ok guys trying to test the fuel pressure but there is no test port on the fuel rail? I know where it should be but its not there? Where can i check this at

 

You should consider a lot of those possibilites should affect the entire engine or every cylinder, but they are worth checking. You have a problem with bank 2 or the back 3 cyls. I would start with what Bustedback said and check for exhaust leaks/cracked manifold. I would also check for vacuum leaks, especially the intake gasket.