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98 XJ dying

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98 XJ sport 4.0 inline 6 210k miles. Drove it to work awhile back and everything was normal. CEL was not on nor were any other warning lights. Several hours later after work and it would not start. It wouldn’t even crank. Tried jumping it and got it started but as soon as I took my foot of the accelerator it died and would not jump start again. It was completely dead, no lights, no radio, no nothing. Got it towed home and life happened and I was unable to work on it for almost 2 months. Finally got some time recently and started digging into it. Initially I thought it was the alternator so I removed it and took it and the battery to AutoZone for testing. They said the battery is still good but it was completely drained so they charged it for me. The alternator passed their test and just in case I took it to another AutoZone and it passed the Regulator portion and Rectifier portion of their test but returned N/A for the Lamp/Diode portion. The guy reran the test and it said the same thing.
So with a fully charged battery and the alternator testing good (kinda) I didn’t know what could be wrong so I bought a code reader. I reinstalled everything and plugged in the code reader and it said “No dtcs”. My first time using a code reader but I’m assuming that means no codes. So I tried starting it and the Jeep started right up. I drove it around the block a few times and again everything was normal, no CEL or any other warning lights. Got back home, shut it off and decided to try it again and nothing. Completely dead again. With the key in On position I get nothing. No door lights, no radio, no dash lights, nothing. Code reader of course returned nothing since the Jeep had no power.
I’ve gone through previous posts on here looking to see if anyone has had something similar but most are saying their battery drained over the course of several hours to several days so doesn’t sound like quite the same problem. Now I’m back to square one unsure what’s wrong. I’m an amateur DIY’er and have acquired most of my auto mechanic “know how” from owning and working on this Jeep, just to give an idea of my level of mechanic knowledge. Is it maybe the alternator since that lamp/diode portion wasn’t testing? What else could it be? Thanks in advance for any and all help!
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How old is your battery? I had a battery fail with an intermittent internal short that would kill it completely without any warning signs, seemingly performing perfectly till it suddenly ended up totally drained for no apparent reason but then recharged OK and worked perfect till it happened again. Really confused me since it tested good when it was working (eventually, my battery charger wouldn't charge it again and detected the internal short).

FWIW, that battery was a two year guarantee O'reilly batteries that failed at one year, eleven months and two weeks (talk about timing!). Replaced it and haven't had that problem since.

Had to replace the alternator a few months later too, always wondered if the battery short could have damaged the alternator or a failing alternator caused the battery failure. The failing alternator gave some really weird symptoms in my case.
 

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I agree with jtec, your first suspect should be loose, dirty, or corroded wire connections in the starting and charging systems. Wires and battery cables can have internal corrosion that is not immediately visible at a glance. When the engine is running, the alternator should be putting out 13.8 - 14.4 volts. 10 minutes after shutdown, the battery should show a resting voltage of 12.6 volts. As fkunc mentioned, a battery can have an internal short, and a bad battery can kill a weak alternator. Batteries should always be tested inside a battery test machine, handheld testers are inaccurate and can pass marginal batteries.




Perform routine maintenance of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Battery terminals and battery wire connectors should bright silver, not dull gray/black and corroded. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, wire brush, and clean until shiny the cable/wire ends and whatever they bolt onto.

Jeeps do not tolerate low voltage, bad wire connections, or poor grounds.


Place your DVOM (Digital Volt Ohm Multi-Meter) on the 20 volt scale. First check battery voltage by placing your multi-meter's positive lead on the battery's positive post ( the actual post, not the clamp ) and the negative lead on the negative post. You need a minimum of 12 volts to continue testing. Next, leave your meter connected and take a reading while the engine is cranking. Record this voltage reading. Now connect your positive lead to the battery terminal stud on the starter and the negative lead to the starter housing. Again, crank the engine and record the voltage reading. If the voltage reading at the starter is not within 1 volt of battery voltage then you have excessive voltage drop in the starter circuit.

Typical voltage drop maximums:
• starter circuit (including starter solenoid) = 0.60 volt
• battery post to battery terminal end = zero volts
• battery main cable (measured end to end) 0.20 volt
• starter solenoid = 0.20 volt
• battery negative post to alternator metal frame = 0.20 volt
• negative main cable to engine block = 0.20 volt
• negative battery post to starter metal frame = 0.30
• battery positive post to alternator b+stud = 0.5 volt with maximum charging load applied (all accessories turned on)
 

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Since you say nothing worked, i'd say if your battery cables look good on both ends, it has to be the battery, maybe take a look at the big square block of wires on the firewall, but no interior lights is a big clue. Maybe there is a fusible link around the battery cable that is loose or whatever.
 

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I agree with what everyone has already said; if it turns out to be corroded cables, I HIGHLY recommend an upgrade from Jeep Cables. I'm not going to link to them and I don't work for them or benefit from the recommendation!!! I got their thickest cables and now I can safely add lights or a winch, etc. Those OEM cables were kind of thin and with a 1998 yours are almost 25 years old.
 

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Just keep in mind a possible bad ignition switch could be suspect. Try and wiggle key around while key is on he on position and see if any dash lights or radio cut in and out and of course try to start it. That’s not a 100% diag but a quick little test before you commit to a tear down and testing.,
 
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