Wierd electrical (non) issue?

92 XJ 4.0l

On Saturday I started up my Jeep and the check engine light came on. It was def. a weak start and I was on my way home from skiing. Didn't think much of it, figured since it was running well and all gauges were where they were supposed to be I'd be fine to get home. Stopped to get gas, light didn't come back on. Snowed Sat night and Sun, so I didn't have the motivation to look into it. Drove it to work Mon. Light back on. Anyway, today is Tues. Light on to work, batt gauge showing I'm not getting a charge (about 12V, not around 14 like usual), and temp gauge reading 20-30 degrees low, very strange. On the way home I turned on the ac to see what would happen, batt gauge back up to normal, temp gauge back to normal. Turn motor on and off, check engine light gone.

That's where it stands now.

Anyone have any insight into this? I just think it's strange and was ready to start chasing it down starting with the batt, alt and volt. reg. Batt tested fine in Sept so I don't think that has anything to do with it.

Sorry about all the abbr., typing on my phone.

Thanks for any ideas and input

possible dead short in the compressor? not real great with electricl stuff, but with the weak start, and the low reading sound possible. I would also retest the battery, witht he weather change, all the gremlins come out in cars.. Would not shock me if the battery was weak...

I wouldn't bet against an issue with the battery cables and/ or grounds. Shake down all the large gauge cables, and double check condition of the doofy braided ground strap from cowl to cylinder head.

JJacobs said:

I wouldn't bet against an issue with the battery cables and/ or grounds. Shake down all the large gauge cables, and double check condition of the doofy braided ground strap from cowl to cylinder head.

Click to expand...

X2 on that good call... sounds like a ground issue

X3 on the grounds and battery cables - check the grounds at the oil dipstick tube and the braided strap from the back of the head to the firewall especially, that braided strap LOVES to corrode because it collects nasty road salt and water in it.

Also, did you happen to have the heat/vent/blower/AC/anything on when you noticed the low voltage reading, and have it off when you didn't notice that? My voltmeter drops 2-3 volts when I turn the blower on high. Battery voltage is actually almost the same, but the voltmeter is far down the chain of undersized power cables that runs everything, including the 30 amp blower motor. Chrysler really thought that one through.

Likely to be just the connections at the battery. Take them apart, and clean the connections with scotchbrite or samdpaper. Clean the debris with spray start or brake cleaner. Reconnect securely. If that doesn't fix it (or just because it is good to do), perform this same process with all of your ground connections under the hood.

When you kicked in the AC, it drew enough current to re-establish the connections, but they need to be cleaned.

Me, if it is electrical I like to start with the battery, the heart of the system.

Pull the cables, charge the battery overnight (good) or for 24 hours (best).

While the battery is charging clean both battery cable ends and measure their resistance--cables can be horribly corroded under the sheathing where you can't see it.

Now that the main cables are cleaned and tested, renew the rest of your grounds, and if you still have the crummy braided ground strap at the back of the head to the firewall replace it with a good cable.

Now that the battery is fully charged, take it in for a load test.

Ok, fully charged battery that passes a load test, cables all up to snuff, good grounds, now it is time to use your multimeter to measure your static voltage, s/b about 12.5 volts, then start the engine and check the voltage again--s/b about 13.8 to 14.5 volts, if not then your alternator/regulator needs testing.

Once all of the above is done, if symptoms persist, you need to start testing different circuits looking for bad wiring/components.