Jeep electrical gremlins (surprise!)

shawn

shawn

running dog lackey of the oppressor class
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Raleigh, NC
The Jeep in question is a 98 TJ, 4cyl, mostly stock electrical system, aside from a Sears/Odyssey AGM battery (group 34, 135 min reserve capacity), some two-way radios, and a Warn 8274. Battery connections are the 'military-style' terminals like these:

terminals.jpg


Each major battery connection (winch, chassis electrical, etc) is on its own side of the terminal, so there's less chance that the winch connection could get hot and cause an open at the chassis connection, etc.

So, long story short, here's the gist of it: Fairly hard winch pull, engine is running at about 2k rpm, we'd been taking breaks to let the winch motor and alternator cool. The log we were dragging got momentarily hung up, the winch bogged down a bit, and the voltmeter in the dash immediately dropped to the peg (less than 9V). Check engine light came on. Engine is still running, winch still pulling, radios still working, cluster still lit up.

Shut it down, checked everything out, nothing seemed amiss. Fired the engine back up, and we're normal again.

My thinking is that if the alternator crapped out (or fusible link opened/connection got hot and opened, etc), the volts should have dropped to 12V or so, and the ALT light (assuming there is one) would have come on.

Could it have been a bad connection between the battery and the chassis power? The alternator kept the engine running, but couldn't see the battery anymore...? I'd think that the alternator field would collapse without a reference voltage, in which case the engine should have quit... but maybe not?

From what little I know about Chrysler Jeeps, they're second only to mid-century British cars for weird electrical problems. But I figured I'd throw this one out there in case anybody has any good ideas on what the source of the problem might be.
 
Mine would drop all the time winching on a car quest battery, did the same thing. I just let off the winch and keep the RPMs up and it would be alright. I got a gel pack something or other blemish battery now, haven't winched on it yet. Shouldn't have caused any problems. I did it several times on mine and never had any problems out of it.
 
The voltmeter will bounce up and down depending on the winch load... but in this case, it dropped to the peg and wouldn't come back.
 
I just assumed it wasn't enough battery to hold the pull, my winch manual said to run a 650+amp battery and I had a 525. Now I have a 800 and the guy at southern battery that I got it from said it would hold winching for 3 times as long. I have stopped my winch a few times completely on a hard pull and it drops the amp hand every time.
 
I just pulled a stump out with my 4.0 tj, brand new yellow top optima, superwinch 9i. I have the same problem, although mine was SUPER loaded. I had to strap the front of my dodge(DRW) to the back of the tj and the winch was dragging both until the Dyneema line broke. Replace that with some Vectran line and changed angles and the stump reluctantly came out. My winch is connected to the side posts on the optima with everything else on top. I think dual batteries and H.O. alternator is the way to fix it.
 
Those Chryslers control the alternator field with the ecm there is no regulator like ford or Chevy use. If the voltage dropped low enough the computer probably thought there was a fault in the charging system and shut off the field current also setting a code and throwing a check engine light. It was running off the weak battery so it was showing low volts on the gauge. Once you shut it off and restarted it cleared the soft fault reapplied field current and everything came back up. That'd be my guess from what I've noticed about Chrysler charging systems at work

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Tim C said:
If the voltage dropped low enough the computer probably thought there was a fault in the charging system and shut off the field current also setting a code and throwing a check engine light. It was running off the weak battery so it was showing low volts on the gauge.
Click to expand...

That sounds plausible... basically pull enough power out of the system to drop the volts below some threshold, ECM freaks out and shuts down the alt... the cluster voltmeter is also coming from the ECM, so it just turns it off as a "warning". There's no way that the voltmeter was showing accurate battery voltage. If the battery was really down to 9V, the engine wouldn't have restarted.

I wish we'd had a meter handy to see whether or not the alt was still charging. But that sounds reasonable.

I'll have to check the codes to see if it stored anything.
 
Soft code wouldnt have stored I dont "think".

I'd ask Jody..
 
My 03 TJ used to do the same thing. I had dual batteries and a mean green alt. On long pulls the voltage gauge would drop off and IIRC there was a batt light on my cluster. No check engine light. Once I shut it down it would all reset and things were fine with the world again. I don't think you have anything to worry about at this point as I think it is a pretty common thing in the TJ's.
 
Some of the early model tj's had problems with the dash cluster and wireing you might do some searches on google for more info on it. Its been a while since I worked on one of them that was having these problems but what you have described seems familiar.

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Jody sent me a text and basically confirmed what everybody said above. :beer:
 
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