Battery died overnight, now won't jumpstart

suprbst · Jul 20, 2011

I left something plugged into the lighter overnight that I should have disconnected when I parked my '00 Limited yesterday evening... a few beers later, and I forgot to go back out & unplug it. So this morning, I go out to head to work, but my remote unlock isn't working - I immediately realized why, but the batteries in the key still worked, so I was able to open the door :spin1:. Turned the key in the ignition, but, of course, no juice. Luckily, the wife hadn't left yet, so I had her pull up & help me jump the Jeep. It turned over fine, but didn't start. I tried a few times, but no dice. Didn't have time to screw with it this morning, so I closed it up & took the other car.

This isn't the first time I've killed or nearly killed the battery (Optima Yellow Top), but this is the first time I've ever had a problem starting it after restoring power to it. It's charging all day while I'm at work, so I'll see if it starts when I get home, but is there anything that could disable fuel or spark when the battery is killed while still letting me turn it over when power is restored (via jumper)?

Tim_MN · Jul 20, 2011

For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator in not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM.

Your symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and will probably stall unless you keep your foot on the gas pedal. The ECU will relearn the idle settings after a short period of driving and the engine will start and idle normally.

Press on the gas pedal as you start and then go for a 10-15 minute drive.

UNCC_99XJ · Jul 20, 2011

Also be aware that for the first couple of stops you make at a light or stop sign, you'll probably have to two foot it (one on the brake and one on the gas slightly) as it still may not have re-learned idle specs and may try to stall out.

suprbst · Jul 20, 2011

Great to hear - not something I'll have to start into yet another round of messing around with electrical stuff on it right now. I will try it out when I get home - thanks!

old_man · Jul 20, 2011

suprbst said:
I left something plugged into the lighter overnight that I should have disconnected when I parked my '00 Limited yesterday evening... a few beers later, and I forgot to go back out & unplug it. So this morning, I go out to head to work, but my remote unlock isn't working - I immediately realized why, but the batteries in the key still worked, so I was able to open the door :spin1:. Turned the key in the ignition, but, of course, no juice. Luckily, the wife hadn't left yet, so I had her pull up & help me jump the Jeep. It turned over fine, but didn't start. I tried a few times, but no dice. Didn't have time to screw with it this morning, so I closed it up & took the other car.

This isn't the first time I've killed or nearly killed the battery (Optima Yellow Top), but this is the first time I've ever had a problem starting it after restoring power to it. It's charging all day while I'm at work, so I'll see if it starts when I get home, but is there anything that could disable fuel or spark when the battery is killed while still letting me turn it over when power is restored (via jumper)?

Yellow tops seem to get real intollerant of discharge with age. I had to can mine. There are tricks to charging them when they get all the way down. Do a search on Google. The ECU needs a certain amount of voltage to work. In many vehicles that voltage level is higher than what it takes to simply crank the vehicle, so it can take a while to get enough charge in to make the ECU work correctly.

O-Gauge Steamer · Jul 21, 2011

UNCC_99XJ said:
Also be aware that for the first couple of stops you make at a light or stop sign, you'll probably have to two foot it (one on the brake and one on the gas slightly) as it still may not have re-learned idle specs and may try to stall out.

If the battery is not fully up, you will have this problem also. When my battery went south last summer I ran into it. Would not idle. Once a hot battery was in place, it idles perfectly.

The default starting map in the PCM is good enough for it to idle and run. It will run rich, but it will run. I have discovered from watching the AFR with a broadband O2 sensor, that it apparently takes 10 or so start/drive cycles before the PCM stops making big changes to the mixture map.

suprbst · Jul 21, 2011

Charged it overnight & it runs fine now, but had to hold the throttle down while starting it. After a couple start/stop cycles, it appears to run as it did before (without measuring the AFR or using any other gauges). Lesson learned - don't leave the Coleman cooler plugged in overnight. Thanks for the good advice & information.

Milford Cubicle II · Jul 21, 2011

old_man said:
Yellow tops seem to get real intollerant of discharge with age. I had to can mine. There are tricks to charging them when they get all the way down. Do a search on Google. The ECU needs a certain amount of voltage to work. In many vehicles that voltage level is higher than what it takes to simply crank the vehicle, so it can take a while to get enough charge in to make the ECU work correctly.

I have a blue top "deep cycle" and it's about the most finicky battery ever. Kinda ironic that I can't deep cycle my "deep cycle" at all. If it gets discharged whatsoever, it's almost impossible to keep it charged. I have to keep it on a 3 amp trickle charger just to keep it charged for more than two or three days :smsoap:

Battery died overnight, now won't jumpstart

suprbst

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Tim_MN

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UNCC_99XJ

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suprbst

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old_man

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O-Gauge Steamer

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suprbst

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Milford Cubicle II

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