89 xj loses all electrical immediately after crank

89 xj 4.0

runs fine

suddenly have this problem, started 2 weeks ago, and its happened twice

turn the key to run, get seatbelt buzzer, dome lights, etc.. electrical seems fine

then

turn it to START, and the instant it starts cranking , all electrical power is GONE, including the clock, dome lights, EVERYTHING. turn it back to off, then run, start, no power at all, TOTALLY DEAD, COMPLETE ELECTRICAL FAILURE, no lights, no buzzers, no cranking no ANYTHING

if you go under the hood and push wires around, or if you just wait (its not clear to me if its pushing wires or just time passing, or maybe just something intermittent happening to make contact again) power comes back to where you can get the seat belt buzzer, clock, dome lights, but when you go to crank it dies again...

then after you repeat all of that, it will start up and drive fine for days

Notes:


Battery and alternator are less than a year old, and im in socal.
When things are running, jeep runs fine even with headlights, A/C, blower, on full blast and driving uphill on the freeway.

Poke things till you narrow it down... check your battery terminals.

Very good indication of a bad battery. Could be very dirty battery connections, but I'll bet lunch on the battery being bad. Easy test - put a volt meter on the battery and try to crank - if voltage drops to 0 then your battery has an internal short.

Can the battery have an intermittent internal short? In other words, can it be shorted and completely lose electrical power, then come back to life and resume completely normally?

DieselSJ said:

Very good indication of a bad battery. Could be very dirty battery connections, but I'll bet lunch on the battery being bad. Easy test - put a volt meter on the battery and try to crank - if voltage drops to 0 then your battery has an internal short.

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Battery voltages:

12.6 engine off
10.9 cranking
14.5 engine on

Measured at the battery terminal clamp bolts.

Is it possible the starter relay is defective and somehow creating an open circuit to the rest of the vehicle?

Battery voltages look OK-ish to me... if it had gotten to 9 you'd have a definite issue. Try measuring the voltage from the frame to the negative battery terminal while cranking, it should not go above a few tenths of a volt and ideally would be near zero.

That isn't possible, the starter relay only controls the starter motor. This is sounding like an issue between the battery negative and frame ground, or between the battery positive and fuses/fusible links/power distribution system.

kastein said:

Battery voltages look OK-ish to me... if it had gotten to 9 you'd have a definite issue. Try measuring the voltage from the frame to the negative battery terminal while cranking, it should not go above a few tenths of a volt and ideally would be near zero.

That isn't possible, the starter relay only controls the starter motor. This is sounding like an issue between the battery negative and frame ground, or between the battery positive and fuses/fusible links/power distribution system.

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I think you are right, its something in the ground cables or distribution, but how would that explain a complete loss of power even when not cranking?

I wish I could get it to fail on command so I could measure voltages while its failed.

The fact that even power to the CLOCK was lost says something. There has to be a complete open circuit for quite awhile.

What about the "B+ latched" line? maybe?

It's a decent guess - though I think that line only powers engine management / fuel injection hardware.

This exact set of symptoms showed up on a friend's 92 XJ a few months ago; he would be driving down the road and everything would go dead. Headlights, motor, interior lights, you name it... same exact problem. He thought it was the NSS and tossed me the keys, I fixed it by looking at the positive battery terminal funny and starting it back up. Turned out the positive terminal had been replaced with one of those shoddy bolt-on ones and the wire inside the bolted down clamp was corroded enough that any random movement would sometimes cause an open circuit.

Thus my "poke random things till it works again" suggestion - carry your voltmeter, random electrical tools, electrical tape, fuses, extra wire of various sizes, crimp terminals etc for a while, whenever it fails write down what caused it to work again and continue. Eventually it will either fail permanently and you will figure out what the problem is, or you will have enough statistical evidence built up that you can figure it out. Just leave a bit earlier than you otherwise would.

Another thing that could cause this issue - corrosion in the bulkhead connector below the clutch master cylinder (or on an auto, below the brake booster and somewhat toward the fender.) If it's a standard, check that connector and the fuse panel under the dashboard for damage caused by leaking brake/clutch fluid.

How clean is the negative battery connection at the block?

I would hit the battery mains--there are items such as the headlights and interior lights that are un-switched and merely protected by fusible links. Too lose ALL power you are getting an open circuit that involves the main battery cables or the one and only unibody ground--the POS braided cable from the rear of the head to the firewall.

Do a voltage drop test on the mains, and clean up all of the grounds including those critical ones at the dipstick tube. Replace the braided strap with a 4 or 2 gauge cable.

And yes, you could have a battery issue (less likely)--have it load tested for grinz and giggles.

I have almost this exact issue. Just started today.

Did you get this resolved, what was the culprit?

acannell said:

89 xj 4.0

runs fine

suddenly have this problem, started 2 weeks ago, and its happened twice

turn the key to run, get seatbelt buzzer, dome lights, etc.. electrical seems fine

then

turn it to START, and the instant it starts cranking , all electrical power is GONE, including the clock, dome lights, EVERYTHING. turn it back to off, then run, start, no power at all, TOTALLY DEAD, COMPLETE ELECTRICAL FAILURE, no lights, no buzzers, no cranking no ANYTHING

if you go under the hood and push wires around, or if you just wait (its not clear to me if its pushing wires or just time passing, or maybe just something intermittent happening to make contact again) power comes back to where you can get the seat belt buzzer, clock, dome lights, but when you go to crank it dies again...

then after you repeat all of that, it will start up and drive fine for days

Notes:


Battery and alternator are less than a year old, and im in socal.
When things are running, jeep runs fine even with headlights, A/C, blower, on full blast and driving uphill on the freeway.

Click to expand...

Replace your ignition switch. The START and RUN circuits run differently in the switch, and it sounds like you're losing the START load (it usually goes first on the old GM columns.)

The switch is cheap, make sure you specify whether you have a tilt column or not, and it's only a pain because you can't see what you're doing (I'm a big guy, so I remove the driver's seat to make the job easier on myself. But, that's about it - the rest can be done by touch.)

Found the problem last night. My rig ran for a week after cleaning all the terminals and connectors, then stopped running again last night. It was the damnedest thing. I'd lose power when I tried to start, get out, slam the door, and the power would come back. Try to start, and lose power again, slam the door, power came back.

I was cleaning the positive connector when when it literally fell off the wires in my hands. Aha!

I loosened up the connector, put the wires in securely, and tightened it really well, so far so good.

5-90 said:

Replace your ignition switch.

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But a bad ign switch won't kill the dome lights. What he really needs is a set of those great cables you make. :}