Owen Shirk

I'm going to try and explain this the best I can...... I have a 2000 XJ with the 4.0 and it has ran really strong up until this point. The engine runs fine when cold/warm but bucks and sounds like im redlining at 2000 rpms and doesn’t get power to the wheels when hot, even during highway speeds unless I kick it in overdrive. It will rev healthy in neutral when hot and slowly accelerate in gear but barely will creep unless I shift it to drive after I’ve rev’d it. Almost like it’s starting in 2nd gear.

I’m sure it’s a combination of things I just know it helps to get opinions when it comes to something like this and this has been a PITA to diagnose

My list to check tomorrow is: spark plugs and if there’s a leaky injector. I just ran an injector flush with Bardahl commercial cleaner from a friend that sells it. Parts I plan on replacing to see if it helps is the front upstream O2 sensor and maybe (hopefully not) one or all shift solenoids, a buddy said it sounds electrical because it sounds like its just going into limp mode.



The only other thing to note is I think my oil pump is going bad, it also runs great when cold/warm but when it gets up to running temps at idle it will drop to 0 and that's actually when the whole rpm/torque/limp mode starts. If anyone can give any insight that would be great. I tried to upload a video but it wouldn't let me

4.3L XJ

How long since you replaced your O2 sensors?

Owen Shirk

I haven’t changed them since I bought the Jeep, the thing that’s stumping me is it’s not throwing a code..

Owen Shirk

Here is the video I couldn’t get to load yesterday.

4.3L XJ

You only get a code for O2 sensors when the heaters in them don't work, or if there zero voltage coming from them. They are just like solar panels, they get weaker over time. Since everything is fine when cold, but has problems when hot, I think this is your problem. When cold the fuel/air mixture is rich. But when warm, the ECU leans it down based on info from the O2 sensor. If the voltage is weak, it results in a lean condition