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Old 12-09-2013, 05:42 PM   #1
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Battery dead now wont hold idle

Left the lights on by accident after taking the wife to work.

Went to jump it and I can get it to start if I pump the gas enough and then even keep it running. The moment I take my foot off the gas it dies.

4.0
10 degrees outside.

Any ideas?

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Old 12-09-2013, 05:48 PM   #2
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Quote:
Originally Posted by BrianTG View Post
Left the lights on by accident after taking the wife to work.

Went to jump it and I can get it to start if I pump the gas enough and then even keep it running. The moment I take my foot off the gas it dies.

4.0
10 degrees outside.

Any ideas?
You probably did this but you made sure to let it run up enough charge? Maybe let it charge for 5-10 minutes before starting her up.

*edit: Normally it shouldn't need such a long charge up period but the battery just could be very dead.

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Old 12-09-2013, 05:58 PM   #3
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Yeah it's not the battery. Cables long gone have lights etc. just won't fire up the way it should.
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Old 12-09-2013, 06:01 PM   #4
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When enough voltage is drained out of the battery the PCM (computer) looses its memory. When you start the Jeep just keep it running the best you can till it relearns the parameters again.
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Old 12-09-2013, 06:04 PM   #5
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How long would you suggest?
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Old 12-09-2013, 06:21 PM   #6
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How old is the battery?...you could have killed it, Jeeps don't run well with a poor battery. Just jumping it isn't good enough and generally takes a good amount of time if you are recharging only using the alternator.
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Old 12-09-2013, 06:32 PM   #7
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Battery's newish.
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Old 12-09-2013, 07:05 PM   #8
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The engine cannot/will not run or idle properly when the battery is dead or nearly dead. Even after jump starting it.

The reason is 12 volts is required by the alternator before it can put out power. The days of being able to run an engine without the battery in place or when it is dead are long-gone. If the alternator doesn't get enough power from the battery, the alternator can't put out enough power for the ignition system.

So if you jump start the engine with a dead battery, the engine will either not idle or will barely idle after you remove the jump start cables. The engine may run for a minute or two with a dead battery after jump starting it but once the magnetic field in the alternator dies after being disconnected from the jump start battery, the alternator will stop providing power.

And for those who have seen vehicles with dead batteries and alternators run just fine, some alternators are "self-exciting" so they don't need 12 volts from the battery. The TJ's alternator is not self-exciting so it requires 12 volts from the battery to work.

The solution is to get a fully charged battery into the Jeep. I would charge it over night with a bench charger, it won't charge in that condition from the TJ's alternator.
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Old 12-10-2013, 10:27 AM   #9
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Did you get it running?
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Old 12-10-2013, 10:35 AM   #10
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It's the battery. Put it on the trickle charger. If it still won't idle get a new battery. It's a very common issue with our Jeeps. I had the same issue when my battery bit the dust. Had to put the pedal to the floor to get it to start, then give it gas to keep it idling until it warmed up. New battery, boom, runs perfect.
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Old 12-10-2013, 11:10 AM   #11
Knows a couple things...

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A trickle charger is great for keeping a battery charged but it isn't a good choice to recharge a dead or nearly dead battery. For that you really need a real bench top charger. 6-10 amps of charging capacity would be a good size for a battery charger to own for home use.
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Old 12-10-2013, 11:21 AM   #12
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Quote:
Originally Posted by Jerry Bransford View Post
A trickle charger is great for keeping a battery charged but it isn't a good choice to recharge a dead or nearly dead battery. For that you really need a real bench top charger. 6-10 amps of charging capacity would be a good size for a battery charger to own for home use.
Whoops, yeah trickle charger is for keeping the battery "topped off" not charging.
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Old 12-10-2013, 11:49 AM   #13
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I had the same problem. Battery died, I jumped it and got it running and then towed my jeep to a run. Started but would not idle. Was a very difficult trail run because of that. Driving around the next day it charged right up and no further problems.

Couple weeks later a buddy came over and we wrenched on her jeep. Not sure what we did but when we finished, her battery was dead. Jumped it and it would not idle.

But I had learned. I just left it jumped to mine for a few minutes and got a decent charge on her battery. Once it would idle I sent her on her way and it charged on the drive home and as far as I know - no more problems.
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Old 12-10-2013, 04:35 PM   #14
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Discharging a battery could also damage the cells. If you do it multiple times, it might not matter if the battery is new or not. It might not be able to hold a full charge. I've had this problem over the years.

If you do discharge the battery, as many have said, it will idle roughly and it will likely die, if you take your foot completely off the gas. So, after jumping it, keep your foot on the gas, just enough to keep it running smoothly. You can drive this way for awhile, and hopefully after 15 to 20 minutes, the battery may be charged enough to start the car on its own. If you come to a stop sign, just make sure you keep the gas pressed enough to keep the idle up to avoid the car stalling on you. Once you get home, you can pull the battery and take it somewhere to have it fully charged. If the battery seems weak afterwards, then the discharge ruined the battery, and you'll need a new one. Discharging a battery can ruin it. So, never allow your battery to discharge. It is crucial to your battery life to make sure you don't leave those lights on, or run the radio for extended periods without the car running.
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Old 12-10-2013, 07:26 PM   #15
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30 degrees today. Charged it for 30 mins and it started. Running fine.

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