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  #1  
Old 02-05-2012, 02:02 PM
bseballkid1990 bseballkid1990 is offline
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Default Battery light comes on when the truck jerks?

Last night when I was on the way home I spun the wheels leaving a red light in the rain and it revved up pretty high and I threw it into 2nd and it was all jerky and the battery light came on so I pulled over and opened the hood and nothing was wrong and when I started her back up it was gone. It's happened a couple other times as well. What's causing this? I just got a new battery and brass connecters like a week ago. Is it something to worry about?
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Old 02-05-2012, 02:23 PM
FireRanger FireRanger is offline
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Default Re: Battery light comes on when the truck jerks?

The light comes on when the key is in the ON position and the alternator is not generating power. It actually has nothing to do with the battery. It is the alternator light... even though they made it look like a battery.

The alternator probably reaching the end of it's useful life. Power generation cutting out at high RPM is a very common symptom of this. Course, usually it comes back on when the RPM comes back down. But I guess it just depends on what component of the voltage regulator is dying. As it continues it's downward spiral, you may notice it happening at lower and lower RPM until it doesn't work at all.
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Old 02-05-2012, 02:49 PM
Rhodyguy Rhodyguy is offline
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Default Re: Battery light comes on when the truck jerks?

also the belt might have been slipping from the water
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Old 02-05-2012, 04:42 PM
FireRanger FireRanger is offline
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Default Re: Battery light comes on when the truck jerks?

I thought about that. But if that was the case, it would have caught and spun back up without having to shut the engine off.
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  #5  
Old 02-05-2012, 10:57 PM
bseballkid1990 bseballkid1990 is offline
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Default Re: Battery light comes on when the truck jerks?

The belt slipping could have been it. It happened a couple times when the truck was jerked and turned off after a few minutes of driving. It just so happened that the other night I stopped to check. How hard are alternators to replace?
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Old 02-06-2012, 08:45 AM
bseballkid1990 bseballkid1990 is offline
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Default Re: Battery light comes on when the truck jerks?

Quote:
Originally Posted by FireRanger View Post
Power generation cutting out at high RPM is a very common symptom of this. Course, usually it comes back on when the RPM comes back down.

I was thinking about this and when I get on it getting on the highway it get's pretty high in the revs in 4th before I shift to 5th. I hit about 70-75 when I'm trying to catch up to traffic pace. It has never happened doing that. Only a couple sudden jerks and wheel spins have caused it. The sudden jerks normally come with spinning my tires.
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Old 02-06-2012, 09:12 AM
FireRanger FireRanger is offline
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Default Re: Battery light comes on when the truck jerks?

Well, try this. Next time you gun it and the alternator cuts out, reduce the electrical load. Turn off the blower, headlights, and wipers. See if it kicks back on. If so, then it is probably belt slippage. Lowering the electrical load lowers the electromagnetic counter-rotational force.
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Old 02-06-2012, 09:43 AM
bseballkid1990 bseballkid1990 is offline
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Default Re: Battery light comes on when the truck jerks?

Quote:
Originally Posted by FireRanger View Post
Well, try this. Next time you gun it and the alternator cuts out, reduce the electrical load. Turn off the blower, headlights, and wipers. See if it kicks back on. If so, then it is probably belt slippage. Lowering the electrical load lowers the electromagnetic counter-rotational force.
I will. Except I rarely use the heat or A/C lol so that's never a problem. My mechanic did say my belt was old though.. Would that contribute to this?
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Old 02-06-2012, 11:18 AM
RoberticusMaximus RoberticusMaximus is offline
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Default Re: Battery light comes on when the truck jerks?

Quote:
Originally Posted by bseballkid1990 View Post
The belt slipping could have been it. It happened a couple times when the truck was jerked and turned off after a few minutes of driving. It just so happened that the other night I stopped to check. How hard are alternators to replace?
Really easy for my 2.5L, 4cyl. Three bolts and disconnecting a heater hose and the electrical plug & ground. about an hour of work plus bringing to core in to wherever. Some places test it for you too.

but, yeah, try a belt first if it needs to be done anyway.
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  #10  
Old 02-06-2012, 11:24 AM
87xlranger 87xlranger is offline
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Default Re: Battery light comes on when the truck jerks?

Test your Battery and alternator first - IT'S FREE!!

A dead cell in your battery can cause the same behavior because the battery isn't taking the charge from the alternator as well.

Troy.
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  #11  
Old 02-06-2012, 12:33 PM
FireRanger FireRanger is offline
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Default Re: Battery light comes on when the truck jerks?

The alternator light has nothing to do with the battery "taking a charge" . As I described before, the only time that light comes on is when the key is ON and the alternator is not generating power. As long as it is generating power, the alternator and the light do not care where it goes or what you do with it.

IF the battery is so dead that the system voltage is too low to provide field current, the alternator will not be able to start generating power. Course it also won't be able to start the truck either so that clearly isn't a factor.

IF the battery internally shits itself while the alternator is running and exceeds the capacity of the alternator, voltage will drop and the alternator won't be able to bootstrap itself. Generation will also cease and the light will come one. This will probably stall out the engine in short order and it won't be able to restart. So this is also not a problem.

So that leaves either an internal failure in the alternator or the belt slipping.
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  #12  
Old 02-06-2012, 12:50 PM
87xlranger 87xlranger is offline
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Default Re: Battery light comes on when the truck jerks?

Getting both tested is still a good idea, regardless of your rational. I have had a battery light come on with my 2000 taurus, the alternator was fine but the battery's dead cell was preventing it from taking a full charge. I put in a new interstate battery over a year ago and no battery light, I'm all ears for your theory of how it worked in my taurus but isn't applicable to a ranger.

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  #13  
Old 02-06-2012, 01:35 PM
FireRanger FireRanger is offline
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Default Re: Battery light comes on when the truck jerks?

The light came on because, as I said, with your shot battery, the system voltage is falling below that which the alternator can use to bootstrap it's field current. This is perfectly plausible in and of itself, but it is not what he is experiencing. Batteries don't just magically die at high RPM then come back to life one you return to normal RPM or restart the engine. It is either dead or it's not. It wouldn't be working fine 95% of the time and starting the truck every day in a case like you're describing.
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How to: Aux light wiring, relays, & fuses
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  #14  
Old 02-06-2012, 04:11 PM
Unclejerr612 Unclejerr612 is offline
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Default Re: Battery light comes on when the truck jerks?

Had the same problem with the alt on my 2.5 about 3000 rpm getting on the freeway or taking off fast from a stop the battery light would come on. checked the alt and the stater was eaten away and brushes were gone bought a new one from napa bingo no more light. I had 100.000 miles on my truck so having had the same problem as you did it looks like it might be the alt.
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  #15  
Old 02-06-2012, 06:08 PM
bseballkid1990 bseballkid1990 is offline
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Default Re: Battery light comes on when the truck jerks?

I revved it high today in first and jerked but nothing. It has a one week old battery so I know it's not a bad battery. I'll get the alternator checked out tomorrow and get back to ya'll.
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