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97 Wrangler. Died in middle of road

matt straut

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Jul 22, 2017
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SC, United States
Won't restart. Error code said ignition coil, I replaced that. Still won't start. Sprayed starter fluid and started, ran. Drove for a half hour, shut off, wouldn't start. Starter fluid- it started. The battery was quite dead from previous tinkerin so I did have to jump it.My wonder is- Could it be the fuel pump if it ran for a half hour around the neighborhood?
 

Jerry Bransford

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The engine ABSOLUTELY will not run for long with a bad/dead battery after being jump-started. The alternator is powered by the battery so if the battery is dead, the alternator will not be able to produce power for the ignition system. The days of being able to drive on a dead battery after jump-starting the engine are long gone for most modern vehicles including Jeeps.

You need to either replace the battery or if it's still ok but just dead, put it on the charger overnight. NO, the alternator has no ability to charge a dead battery because, again, the alternator actually runs off voltage provided solely by the battery. And no, just a couple hours on a battery charger is not likely to be good enough. It needs a good overnight charge to recover and there's no guarantee it will recover after being drained dead.

And if charging it overnight doesn't help, the battery is toast. The only way to verify the battery's true health is to have a battery shop (or some battery retailers) perform what is called a "load test" which puts a heavy load on the battery to see if it can put out sufficient power under load.
 

Mike_H

Off-Camber is scary
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could you elaborate, Jerry? If the battery is powering the alternator, than what is the point of the pulley on the alternator?

I agree that it's not good to charge the battery with the engine running, way better to use a battery charger, but the alternator will charge it...static charge is 12.xxx volts, but when a vehicle is running, it's 14.4. That extra voltage goes through the regulator until the battery reaches equilibrium and the change is "shut off"

To the OP, if your alternator is shot, it can describe what your seeing. The battery will power the vehicle for a while, but without the alternator producing charge, it won't maintain for indefinitely.
 

Jerry Bransford

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could you elaborate, Jerry? If the battery is powering the alternator, than what is the point of the pulley on the alternator?

I agree that it's not good to charge the battery with the engine running, way better to use a battery charger, but the alternator will charge it...static charge is 12.xxx volts, but when a vehicle is running, it's 14.4. That extra voltage goes through the regulator until the battery reaches equilibrium and the change is "shut off"

To the OP, if your alternator is shot, it can describe what your seeing. The battery will power the vehicle for a while, but without the alternator producing charge, it won't maintain for indefinitely.
The battery is only powering the alternator's exciter coil, it's not providing the rest of the power the alternator generates.

If you were to disconnect the battery while the engine was running, which is not good for the alternator, the engine would die within a few minutes, as soon as magnetic field generated by the exciter dies. When my wife's battery suddenly went nearly dead, I had to jump start her Grand Cherokee 5-6 times during the 3-4 mile drive to the battery shop.
 
Last edited:

lovemachine

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Feb 13, 2017
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985
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Indiana
Huh. I was always told that when you buy a brand new battery, it's never 100% charged. So when you install the new battery, you should let the engine run a bit to allow the alternator to charge the battery 100%.

Had no idea.
 

Jerry Bransford

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Huh. I was always told that when you buy a brand new battery, it's never 100% charged. So when you install the new battery, you should let the engine run a bit to allow the alternator to charge the battery 100%.

Had no idea.
The alternator is fine charging a partially discharged battery, that's its job of course, it's just not designed to charge a completely or mostly discharged battery.
 
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Mike_H

Off-Camber is scary
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The battery is only powering the alternator's exciter coil, it's not providing the rest of the power the alternator generates.

If you were to disconnect the battery while the engine was running, which is not good for the alternator, the engine would die within a few minutes, as soon as magnetic field generated by the exciter dies. When my wife's battery suddenly went nearly dead, I had to jump start her Grand Cherokee 5-6 times during the 3-4 mile drive to the battery shop.


Ok, that makes more sense. I understand now. Thanks !