Hello,
I've been trying to diagnose and remedy this for a long time now, and I'm running out of ideas fast.

1996 XJ 4.0

After about an hour or so of operation, I'll experience a significant loss in power. It will idle just fine but when trying to accelerate things will just go to hell. Engine will hesitate, lose power, sometimes backfire. If I clear the code or disconnect the battery things will run fine again, for a time.

Torque app reports both o2 sensors have 0 volts and fuel trim in the 30s when having trying to accelerate, but things will return to normal at idle.

I've replaced o2 sensors, MAP sensor, exhaust manifold, checked tps, fuel pressure seems fine (though admittedly I could not test it while trying to accelerate), I cannot find any vacuum or exhaust leaks aside from things I've already taken care of.

I'm running out of things to check and replace.

Has anyone experienced, or better yet fixed a similar problem?

Thanks.

 

Hello, I would suggest verifying fuel pressure (with a guage) couls possibly not have enough under load.

 

How can I test while under load?

Pardon my ignorance, I'm just not sure how I can have the pressure gauge attached and readable while driving.

 

They do have pressure gauges with a hose long enough to tuck the guage under the wiper blade. Or when it acts up , have a helper try to "brake torque" and load the engine while you observe the guage . Does the 96 still have the fuel filter on left side frame rail near tank? have you changed the filter?

 

Yes, brand new filter, and I should point out, brand new pump as well.

I really doubt fuel pressure is the problem.

 

you check the o2 sensor signal circuit, could very well be a wiring issue.