i have a 96 xj and i have been having alot of problems with it running rough. when you drive down the road normally it drives fine but once you let it sit and idle for like fifteen twenty min it runs horrible, it loads up and misfires i think so you have to rev it up and finally it will clear. Also if you go in the woods in no time at all it will start to run bad and have like absolutly no power. At one point after it sat and ran for a little while the check engine light came on and the code was po171 which is a lean or rich mixture. I looked up online and found alot of people with the same code replaced either the coil, o2 sensor, or a fuel filter and that fixed the problem. So i changed all of those with no luck, the code has never come back on but it will still run that way. I swapped out my injectors awhile back with neon ones so i swapped the stock back in and it still did it. so i have two new o2 sensors, new coil, fuel filter, plugs, fairly new cap rotor and wires, and it still runs weird. I have checked for vacum leaks and anything else that is out of place. I also checked fuel pressure which is like 35 psi running and like 45-40 at prime. Anybody have any ideas or any advice would be greatly appriciated.

 

try checking your idle control valve or throttle position sensor. worked on mine. good luck!

 

how do you test those

 

Or camshaft position sensor. Mine went out and no one could figure it out. Finally found a 4x4 mechanic and he squared it away.

 

$100 says its an 02 sensor.

 

i have two new o2 sensors

 

Before you pay up, I don't think he specified where he got the o2 sensors, one of the new ones could be bad if he got cheap ones.

 

no i bought good ones, i dont buy junk for my jeep.

 

Which ones did you buy?

I had a very similar problem to the one you're having and I replaced my upstream sensor a couple months back... in doing my research I found an ABUNDANCE of warnings to get only the NTK sensor (available at NAPA). The Bosch and Denso seem to give folks a lot of trouble, especially the former.

I drove an extra 20 minutes to get the NTK and i'm glad I did. She has been running fine since... well, relative to before anyway.

 

ya i have a ntk upstream thats like two weeks old and a bosch downstream thats maybe close to a year old not even.

 

Hold the phone. I'm 98% sure that the fuel pressure spec for a 96 is 49 psi, plus or minus 5 psi.

You mentioned that you have 35 psi when running? I'd verify that fuel pressure spec, but if it is 49 and you have only 35, you must resolve that before looking anywhere else!!

 

hmm you think that the fuel pressure should really be that much. i told a buddy of mine that it was at 35 when running and he thought that was kinda low but he wasnt too sure. does anynody know for sure what my fuel pressure should be at.

 

96 and later...46-51 at idle, if you fall into 95 and earlier(sometimes they used up some of previous years stuff before swapping over) with vacuum hose attached to fuel pressure reg.(31-33) vacuum hose detached(39-41)psi hope this helps. all specs at idle

 

i dont even know where my regulator is on this thing. i seen people say they are right on the fuel rail but not on mine. is it on the pump in the tank or something or does mine not even have one. maybe i do have a fuel pump issue because also when i nail the thing goin down the road its like sluggish at wide open then if you back off the gas a hair it gains a lot more power

 

Mine were brand new too. Right befor I dunked them in a deep water hole one day out. Funny thing happen as i left my spot. Just enough time for the "CHeck Engine" Light to come on and start a rough idle then as i drive away backfire REEEAL bad, like gunshots outta the header.