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Unread 04-03-2012, 06:32 AM   #1
elCapitan28
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Voltage problems, new batt and alt

Here's the whole story, and not sure which parts matter and which don't:

2000 Cherokee (XJ) getting new fender flares, required some welding on the body. Pretty sure the guy that did the welding didn't disconnect the battery first.

Wouldn't start, so replaced some fuses. Turns out fuel pump fuse was bad. Started fine.

1/2 block later, lights went dim, lost power. Got a jump, then did the same things. OK, so I'm thinking alternator.

Replaced the alternator and decided a 4 yr old battery wasn't good either, so replaced that as well, same day.

Now the Jeep starts, voltmeter goes to 12 (should be at 14), sits for a while, then check engine light comes on. A few seconds later, voltmeter bottoms out suddenly, and check guages light comes on. If I stop then restart the car, same thing happens. Up to 12 for a bit, then check engine, sudden drop in volts and a check guages light.

Other people with similar problems usually end up blaming the alternator, but this one's brand new. I've double checked all connections, making sure they're clean and solid. I've heard one person say maybe a loose belt? Or maybe the stock ground lead off the battery is just too old and may be frayed on the inside?

Any help would be appreciated. Gotta get to Moab for Easter Jeep Safari this weekend! Thanks!

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Unread 04-03-2012, 06:48 AM   #2
CJ7-Tim
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If you bought a cheap "lifetime warranty" alternator from Advance/IdiotZone/O'Reilly's, test the output at the terminals on the rear of the alternator. A fair number of those cheap parts are not correctly rebuilt.

Inspect the the battery/starter/alternator wires and connectors for damage or corrosion.
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Unread 04-03-2012, 07:00 AM   #3
elCapitan28
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Dang, tim, is this all you do all day? You're everywhere on this forum!

Thanks for a quick response. Wife's taking it for a batt & alt test this morning, and I'll be checking and/or replacing grounds today. I'll let you know.
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Unread 04-03-2012, 03:10 PM   #4
elCapitan28
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No dice. Alternator's good, completely replaced pos and neg battery leads and terminals, brushed other grounds clean.

Still the same problem. With the key in the on pos'n, only goes up to 12V, and after starting, same thing, only up to 12V. I haven't sat with it very long or driven it to see if it drops to 9 like before, but either way, 12V is not 14V.

Another guy said maybe there's a "fusable link" where the fuse is blown? If he means the lead from the alternator up to the fuse box on the fender cover, I checked that with a light, and the connection's good.

Could the computer be fried from the welding?

Last edited by elCapitan28; 04-03-2012 at 03:32 PM..
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Unread 04-03-2012, 03:20 PM   #5
CJ7-Tim
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The voltage gauge is a reliable indicator of your charging system functions. If it show 9 volts, or 19 volts, there is a problem. It should show a constant 13.8-14.4 volts at 1500 rpm and higher. Either the alternator is not functioning correctly, the wires or wire connectors are faulty, or the battery has an issue.

There is a fusible link however, it is a fuse. It is either is good, or bad. If bad, I doubt the engine would start/run. The ECU computer controls charging and welding on or near the Jeep should have no effect on it.
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Unread 04-03-2012, 03:46 PM   #6
elCapitan28
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We've had both the old and new alternators tested and both came out clean, no problems. Like I said, new battery and new leads from both pos and neg from battery. ...I'm at a loss
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Unread 04-03-2012, 04:45 PM   #7
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You mentioned the "check engine light" went on.

Strategy for a check engine light is always the same. Read the codes.

Post them here for comment. Codes are invaluable in troubleshooting.
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Unread 04-03-2012, 06:22 PM   #8
elCapitan28
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code was for the O2 sensor, already checked

welding on or near a Jeep, especially a unibody, should have no effect as long as the battery terminal's disconnected, but I'm pretty sure the welder didn't disconnect. I'm still stuck on the computer being the problem, since nothing else has solved it that anyone's mentioned, and a bad computer could certainly cause this. ...not that I'm ungrateful for the help!
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Unread 04-04-2012, 12:59 AM   #9
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You already established that the alternator is good, battery and battery connections are good, and you know that the battery is being drained out. Okay, hang on you're almost there... Yes the ECU manages the alt output, before you go there, a few things you need to rule out.

First of when you said you've checked the lead from alt to fuse box with a light, what do you mean? You need to check that you have electrical continuity between the alternator's connector and the box (voltmeter in continuity test mode), fusable link can pose a challenge to assess visually.

Then there is the possibility of a major current draw, more likely on accessories powered past ignition, which would explain the big voltage drop. And... you did mention a blown fuse, right? Big red flag.

I think you're overthinking the neg bat and the welding thing. The hazard posed by the welder is more heat related than electrical in nature. Your Jeep could be struck by lighting, that wouldn't make a dent on the electrical. Having said that, there is one thing that bugs me. The O2 code. Heard about damaged O2 sensor wires shorting out the ECU (spark from welder would make sense here).
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Unread 04-04-2012, 06:25 AM   #10
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Ah, OK. Didn't know fusable links had to be checked that way. I was using a simple test light (aligator clamp to ground, needle to ends of lead). I'll give it a go with a voltmeter in continuity mode.

Since time is limited before Easter Jeep Safari (I'm really DYING to get this figured out!) I've got a computer on the way just in case. I'll keep you updated.

Seriously, thanks for all the help, and such fast responses!
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Unread 04-04-2012, 08:44 AM   #11
CJ7-Tim
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I welded on my Cherokee several times, no disconnecting, just let it rip. Done it on other XJ's also, no issues. The ECU is is very robust and about the only thing that can damage the ECU is a faulty Crankshaft Position Sensor or a direct short circuit to the ECU.

Did you get the alternator and battery Load Tested, where it is put in a machine and a simulated work load is applied ? Handheld testers are inaccurate, and will often pass marginal parts. The battery should show 12.3 or more volts measured at the terminals 20-30 minutes after engine shutdown and after 12 hours of resting the voltage should be the same.

Are you having a charging issue and not getting a good charge, a battery issues with a dead cell, or a voltage draw that is running down the battery overnight ?
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Unread 04-04-2012, 01:38 PM   #12
elCapitan28
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Yes, both alternator and battery were taken in and tested in-store.

I get what you're saying about the welding, that it's probably not the direct cause, (I think a spark to the o2 sensor wire is most likely), but for future readers, I wouldn't really recommend welding on a car without disconnecting. Yes, you can probably do it without problems for your entire life, but that's only "probably." Depending on where you're welding, where you're grounded, etc. it can potentially flow where it shouldn't and fry things. Seen it. Might as well avoid it by taking an extra 20 second to undo a terminal. Low risk, you're right, but a quick fix for 0 risk? Even better.

But, back to the issue at hand. Yes, it's a charging issue. As I stated in the beginning, it never gets up to 14, just to 12, then suddenly drops to bottom-line; It's not an overnight drain. And the battery appears to be just fine according to all tests, so not a bad cell.

I'll know more this evening when I can properly test the fusable link, and the computer will be here Thursday morning if that doesn't work.
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Unread 04-04-2012, 02:12 PM   #13
TravsXJ
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Would it be worth while to put a meter straight on the battery to verify that your dashboard guage is reporting acuratly?
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Unread 04-04-2012, 04:36 PM   #14
15tcherokee
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I encountered the same problem on my way home today, volts would go up to about 9 then drop dead and the gauge light would come on. NO welding has been done on my jeep at any point. Did recently do the headlight replacement, including harness, so im thinking that may have something to do with it. have to get battery and alternator tested tough. If it is my alternator, anyone have a favorite replacement?
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Unread 04-04-2012, 07:31 PM   #15
elCapitan28
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OK, checked with a multimeter on continuity, and here are the results, but someone will have to tell me what they mean for a fusable lead

With the key in the OFF pos'n: anywhere from 0.1 to 1.0 ohms
With the key in the ON pos'n: anywhere from 1.5 to 5.0 ohms steady, jumps to ~25.0

usually started higher, then dropped. If I moved the contacts around, I could get it to fluxuate a bit. I'm assuming this has something to do with how good of a connection the wands have?

Anyway, bottom line question is... is the fusable lead still good, or no?

TIA
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