Helping a friend, 96' electrical issue

[Demonoid369]

So a friends 96' 4.0l xj is having a electrical issue.
From what has been said:
1. If it isn't driven for more than 2 days, battery dies, needs charging, not jump starting to run again.
2. Battery fries itself after about a month.
3. Brand new battery and alternator
4. Check engine code give O2 sensor bad, she replaced it and the code is still there.
5. Has dummy lights for gauge cluster so no real way for her to test voltage(she wouldn't be able to do a bolt test herself anyway)

Any ideas? I find it strange that there seems to be a parasitic power loss somewhere and fried battery but I'm wondering if the battery frying is its own separate issue?

 

[8Mud]

I've had some batteries tolerate a few total discharges, some not so much.

You really have to do some quick volt tests to see how the regulator is working.

A lot of possibilities for an overnight voltage drain.

 

[Green Mesa XJ]

Are you going to be there working on it?
If you're relaying advice to someone who can't do some of it on her own, we might need to come up with more simplified tests.

One of the things I did to hunt battery drain was disconnect and reconnect the negative terminal listing for relays or other things powering up.

Other thing I suggest is to get a test done at autozone (or wherever)to see what the alternator is doing. They can test the battery as well.
If the alternator is over charging it can kill the battery, I think this is still controlled in the ECM in the 96. So even if the alternator is new and works correctly the voltage regulator is in the computer/ECM.

Checking the wiring for the o2 sensor(s?) might be a good idea too.
Is there just one in the 96 ?




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[Saudade]

So a friends 96' 4.0l xj is having a electrical issue.

4. Check engine code give O2 sensor bad, she replaced it and the code is still there.

What was the code?

 

[Ffredd]

Two O2 sensors in a 96. One on the down pipe and one after the cat.

 

[RedHeep]

Disconnect the negative battery terminal. Hook up the positive lead of your multimeter to the negative terminal and the negative lead of the meter to ground.

You should see voltage since there's an undiagnosed power draw. It might even be over 2 amps.

Pull one fuse at a time until the voltage draw disappears. The fuse that you pull that makes the voltage go to zero is the circuit that's causing the battery to drain. After you find the circuit, you need to figure out why it's shorted. But in the mean time, you can leave that fuse out and it won't kill the battery.