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Just to clarify...

nb11

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I think I have a bad alternator, but I'd like to ask some opinions real quick. I was out and about today in my truck and everything was fine. I ran in Lowe's for a few items and when I came out and started my truck, it started fine then instantly died. I had to keep it above 2k rpm to keep it from dying, and drove with 3 feet to milk it home.

I'm pretty sure it would be the battery or alternator, and I'm leaning towards alternator. About a month ago I was doing some work on my girlfriend's grandfather's '66 mustang and it had the same problem. Ran in the store, came out and it wouldn't run right. $50, new alternator, good to go.

I'm gonna pull my alternator out tomorrow and have it tested, but I'd just like to make sure I'm not missing something obvious here.

I was actually on a mission to get some stuff to try to fix my motorcycle. It wouldn't start this morning, so I had to drive my truck. When it rains, it pours I suppose. Thanks in advance guys.
 


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Could be the alternator...but my Tempo alternator blew about 20 minutes from the jy and I could not drive it once the battery died...had to walk to the jy, buy an alternator and got a ride back to my car...installed alternator and drove on...

If you could drive it home, even having to keep the revs up, may mean something else is wrong...

Does the starter turn the truck over or is the battery completely dead now?
 

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Sounds like a dying alternator. The higher engine speed milks a little more out of it.

Keep in mind a dead alternator can damage the battery and a dead battery can damage a new alternator. Best to replace them as a set or at least charge the battery on a proper charger.
 

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could still be the alternator, just that it is undercharging (the reason you have to keep the rev's up)

If it was the battery, it would probably drive fine once the truck was started.

a simple check get the truck running and take a voltmeter out and check the voltage at the battery. it should be ~13.5 volts or so. with the truck off, the battery should read 12.

If the voltage accross the battery is 12 or less when running, alternator is probably shot..

AJ
 

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No, it'll turn over fine. However, when I first started to leave the store, I didn't realize I had to keep it revved up to keep it from dying out, so I cranked it sever times and I could hear it getting weak.

I keep thinking alternator because 1) I just had the same exact symptoms in the Mustang, and a new alternator took care of it; and 2) I noticed my amp guage was moving around a good bit. At one point, I was holding the engine at a constant speed and flashed my lights and the guage went down about 1/8 inch.

I have had vehicles completely die when the alternator went bad. However, I've also had/heard of them not completely dying all at once (again, just experienced this with the '66).
 

nb11

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Sounds like a dying alternator. The higher engine speed milks a little more out of it.

Keep in mind a dead alternator can damage the battery and a dead battery can damage a new alternator. Best to replace them as a set or at least charge the battery on a proper charger.
Not a bad idea. The battery that's in it isn't terribly old, but I may take this as an opportunity to upgrade. I'll have it tested at the parts store tomorrow just to see what they say, and I'll definitely put a good charge on it if I don't buy a new one.

could still be the alternator, just that it is undercharging (the reason you have to keep the rev's up)

If it was the battery, it would probably drive fine once the truck was started.

a simple check get the truck running and take a voltmeter out and check the voltage at the battery. it should be ~13.5 volts or so. with the truck off, the battery should read 12.

If the voltage accross the battery is 12 or less when running, alternator is probably shot..

AJ
I also makes sense to me that a bad battery would run ok if it was constantly being recharged properly. I'll just pull the alternator and battery to have them tested, as I neither have a good volt meter nor do I have someone to help keep the engine going AND read the meter.

Thanks for your input, guys.
 

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my 99 did about the same thing... it was the alt. but im not about to tell you to throw parts at it, have yours tested before buying new ones
 

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Well your 1st mistake was going to lowe's lol. I had a similar problem with a chevy corsica, I replaced the alt and batt. It still kept dying, I never figured out where the short was. Luckily I got a ford after that, problem solved.
 

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Keep in mind a dead alternator can damage the battery and a dead battery can damage a new alternator. Best to replace them as a set or at least charge the battery on a proper charger.
Quick and Simple Checklist:
Battery Voltage- 12.7 Volts (engine off)
13.5-14.4 Volts (engine on)
Alternator Voltage-
Engine idle, No Load: About 14 Volts
Low Battery voltage will damage Starters
(Check once a month!)
 

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No, it'll turn over fine. However, when I first started to leave the store, I didn't realize I had to keep it revved up to keep it from dying out, so I cranked it sever times and I could hear it getting weak.

I keep thinking alternator because 1) I just had the same exact symptoms in the Mustang, and a new alternator took care of it; and 2) I noticed my amp guage was moving around a good bit. At one point, I was holding the engine at a constant speed and flashed my lights and the guage went down about 1/8 inch.

I have had vehicles completely die when the alternator went bad. However, I've also had/heard of them not completely dying all at once (again, just experienced this with the '66).
I did the same thing about flashing the lights, and my truck completely died on me doing 40mph. Pretty scary actually, the brakes barley work and no power steering going down hill. Funny thing is I was on my way to getting a new battery too. Well I got a ride from my friend to get a new battery and put it in and its been good ever since.
 

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you can also take the truck to autozone/ oreilly's/ advance and they should be able to actually load test the battery and test the alternator without removing them from the vehicle.

AJ
 

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you can also take the truck to autozone/ oreilly's/ advance and they should be able to actually load test the battery and test the alternator without removing them from the vehicle.

AJ
i never trusted that thing when i worked at autozone. the tester inside the store is much better. several times the little mobile tester would read that everything was fine while it was in the vehicle, but take it inside and it would read differently.

anytime i need stuff checked, i remove it and take it inside
 

nb11

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I put a new alternator in today. Got it up to operating temp, played with different accessories and all, and the needle still twitches a little, but I don't remember how much is normal. I think it's fine though. Had the old alternator tested this morning and it did pass, but wasn't putting out as much as I wanted it to. My theory (I may be talking out of my ass) is that as the old alternator heated up, it shorted or whatever internally and failed. Could be wrong, but with a new alternator my truck didn't leave me stranded.

Had the battery tested, too. It's supposed to put out 545 amps, and it was putting out 499 amps but the machine still said it was a good battery. I brought it home and put it on charge for a couple hours. Tomorrow, I'll borrow a volt meter from somewhere and check the power across the terminals with the engine off and with it running so see what it says.

I'm pretty sure the little twitch in the needle isn't anything to be concerned with. Again, thanks for all the input and advice.
 

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