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iBran
 
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Battery/Electrical Troubleshooting

A couple weeks ago, the battery in my GF's 1998 Jeep Grand Cherokee (I6) gave up. It was still under warranty (yay Mopar), so we brought it to the dealer to exchange it. Installed the new one and she didn't have any issues until last week.

If she lets it sit for more than 12 hours or so, it won't start. (She parks outside, and it does get cold here in Minneapolis--below zero most overnights). She parked it at my place last night, and when we went to start it, the battery measured 11.5 volts. Wouldn't turn. I pulled my car around and jumped it. It started, but it would die as soon as the engine came down to idle speed. Started it again, kept it revved to ~2000 RPM for about 10 minutes, and then it would finally keep itself running. FWIW, as soon as the engine starts, the battery gauge (and my multimeter) shows 14.4V.

Here's my theory: The replacement battery is defective or just plain shot. The alternator is struggling to charge the battery and keep all the electrics running, which is why it wants to die right away. As soon as the battery has a reasonable charge, the engine can keep itself going. It has no trouble idling or struggling to stay running AFTER it starts, and it will re-start without trouble as long as she tries within a few hours.

So, here's where I'm stuck: What's my next task for troubleshooting?
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Old 01-11-2010, 06:11 PM iBran is offline  
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pepperochini
 
maybe the alternator is shot?
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Old 01-11-2010, 06:25 PM pepperochini is offline  
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Something's draining the batteries power it sounds like.

Do you get 14.4 when idling for a bit of time?
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Last edited by Viperoni; 01-11-2010 at 06:38 PM..
Old 01-11-2010, 06:31 PM Viperoni is offline  
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iBran
 
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Quote:
Originally Posted by Viperoni View Post
Something's draining the batteries power it sounds like.

Do you get 14.4 when idling for a bit of time?
Yes. Once the engine starts up it hits 14.4 and stays there.

Where/how does one start troubleshooting a power "leak"? I've already checked for obvious things like lights left on.
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Old 01-11-2010, 06:45 PM iBran is offline  
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iBran
 
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Quote:
Originally Posted by pepperochini View Post
maybe the alternator is shot?

Seems to me the alternator is okay if it's able to charge the battery and provide normal power (14V) to the components. How would I go about checking the alternator?
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Old 01-11-2010, 06:47 PM iBran is offline  
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Bill Brasky
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You know, it's really funny. I had a friend of mine have this exact thing happen to her 98 Grand Cherokee with the 4L...

It wasn't the alternator at all. I think she just replaced the battery and everything was good.
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Old 01-11-2010, 08:03 PM Bill Brasky is offline  
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u467
 
connect an ammeter in series between the battery and car, you shouldn't be pulling more than 0.010 A with the car off.
Old 01-11-2010, 09:14 PM u467 is offline  
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godofcheese
 
haul the whole thing down to autozone. They can test both for free.
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Old 01-12-2010, 10:30 AM godofcheese is offline  
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Quote:
Originally Posted by u467 View Post
connect an ammeter in series between the battery and car, you shouldn't be pulling more than 0.010 A with the car off.
++

If you measure a high current between battery and car, get at the fuse box, and pull fuses one by one and measure the current by sticking the multimeter leads in the fusebox where you pulled the fuse from.

If you don't measure a high current, there's a good chance that the new battery itself is fucked. Everything made nowadays is cost-reduced, penny-pinched crap, and car batteries aren't an exception.
Old 01-12-2010, 12:58 PM gee is offline  
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[H]ard|On
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Sounds like you need a new battery. Are there tags on the old one containing a date?

If voltage is up when car is running your alt is okay 99% of the time.
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Old 01-12-2010, 02:40 PM [H]ard|On is offline  
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