# battery/alt/charge question



## davidluster (Sep 16, 2008)

This morning all of the sudden my battery light came on. I was off so I was running some errands. As soon as I am leaving first location my truck dies. 

I had a load that I had to deliver immediately so I went to drop it off. After unloading trailer I had to get jumped again. 

This time headed to parts house. My gauges arent working, air is barely blowing, radio is off, windows wont go down. About half way to parts house everything comes on, gauges come up, all but battery gauge and battery light is still on. 

Then as I am pulling into the parts house battery light goes off and gauge goes up to where it normally is. 

So the guy tests it at 12 something volts, and 95% charged with engine off. By this time I was in a huge hurry to get to an appointment and didnt think about getting voltagge with engine running. So I bought a new battery. 

Then as I am driving off it hits me that I may have just gotten hosed. 

I am thinking my alternator is the culprit and the battery was fine.


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## christmas racing (Sep 1, 2010)

I can tell you your alternator is bad . The next time the batt. light comes on open your hood tap on alt. with a hammer tap not hit . Check the light if it's not off then tap it a little harder . Check light if it's off it's your alternator . This is not a fix all it will tell you is that the alt. is in deed bad and needs to be replaced . Hope this helps .


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## davidluster (Sep 16, 2008)

What does the tapping do?

Also wondering why it tested 95% charged if the alt is bad.


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## mudcatz71 (Jun 8, 2006)

he is right mine did the same exact thing your's seems to be doing. You got brushes in there and wires that may be sticking or loose the tapping will free up or wires may contact again.


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## mudcatz71 (Jun 8, 2006)

you truck would not of died if your alt was charging like it should. your alt started working before you reached the parts house and charged your good bat like it should


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## davidluster (Sep 16, 2008)

Got it. Thx for the info. Guess I'll go back tomorrow and see if I can get my money back on the battery and get an alternator.


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## carryyourbooks (Feb 13, 2009)

what was the problem in the end? i was gonna suggest to check the chassis ground.


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## 47741 (Jan 5, 2010)

I'm with carry on this. You should check your cables. They may very well be worn.

If the battery terminals read about 13.5 (maybe up to 14.x if accessories are on) when the truck is running, the alternator is doing its thing for the most likely. Only other thing to check would be to check diodes to make sure that's going swell


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## davidluster (Sep 16, 2008)

this morning i tapped on the alt after cranking and the battery light went out. Then i got to work and after killing it and did it again. This time the light didnt go off. So i revved it up to about 4k rpms and the light flickered and went out. 

I put some liquid electrical tape (not real sure why) on my posts about a month ago. Could that be preventing me from getting a good connection?


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## davidluster (Sep 16, 2008)

Anyone with an idea as to why the battery read 95% charged? Would the batter go from dead to almost full within 10 minutes of driving if the alt was intermittent?


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## 47741 (Jan 5, 2010)

It wouldn't fully charge in that short of a period. You might get a surface charge that would look like normal voltage, but it wouldn't have any amps behind it- It would be dead as soon as you put a load on it.


Have you looked at your connections to make sure they aren't rotten or loose?


If you can't measure voltage, its pointless to try and guess which part is failing


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## davidluster (Sep 16, 2008)

SaltyTX said:


> It wouldn't fully charge in that short of a period. You might get a surface charge that would look like normal voltage, but it wouldn't have any amps behind it- It would be dead as soon as you put a load on it.
> 
> Have you looked at your connections to make sure they aren't rotten or loose?
> 
> If you can't measure voltage, its pointless to try and guess which part is failing


With the old battery before I changed it I cranked the truck 8-10 times with no problem when I got to store. It wouldnt crank before I got to store without a jump.

Connections are good as far as tight and not rotten best I can tell. I replaced neg cable about a month ago and coated both sided with liquid electrical tape. I am going at lunch to have the alternator tested.


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## bobbyoshay (Nov 29, 2008)

i had a problem with my f-150 not to long ago that my alternator was going out. it would intermittently work and charge. one day a dead battery or too weak to start truck and then i would jump. took battery and it tested fine. i replaced alternator and its been perfect every since. i dont believe your alt has to just go out to cause alot of problems....it can not be fulling charging and still give you headaches.


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## davidluster (Sep 16, 2008)

Alternator tested bad. So looks like my night is planned out.


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## carryyourbooks (Feb 13, 2009)

did that fix it?


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## davidluster (Sep 16, 2008)

yep. So far. Changed the alt last night and the battery light didnt come on last night or so far today. $300 later, the light is off.


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## Knot Kidding (Jan 7, 2009)

Knot knowing what kind of vehicle your driving but, you could have a slipping pulley on your altenator. Changed mine last year for similar reasons as yours. When belt was off I could spin the pulley and grab it to stop it abrubtly and could see the altenator spin about another revolution.


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## davidluster (Sep 16, 2008)

It's an F150. so far light is still off, but now CEL is on and truck is running real rough and dies every now and then at a stop light. 
I am pretty sure its not related to alt/battery. It was idling rough before all this happened.


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## mudcatz71 (Jun 8, 2006)

Just for grins check out where your ecm grounds to the frame for the ruff idling. If your ecm is not geting the proper voltage it will do that. Rust mud dirt road grime water will cause that.


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## Chief5x5 (Apr 25, 2005)

*Rough Idle*



davidluster said:


> It's an F150. so far light is still off, but now CEL is on and truck is running real rough and dies every now and then at a stop light.
> I am pretty sure its not related to alt/battery. It was idling rough before all this happened.


Check the water level, when cool, in the radiator. On Board Computer may be trying to keep the engine cool by shuting other things down.


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## davidluster (Sep 16, 2008)

mudcatz71 said:


> Just for grins check out where your ecm grounds to the frame for the ruff idling. If your ecm is not geting the proper voltage it will do that. Rust mud dirt road grime water will cause that.


What is ECM?


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## Chief5x5 (Apr 25, 2005)

*ECM*

Electronics Control Module.


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## davidluster (Sep 16, 2008)

I got the codes today. P0171 & p0174. Bank 1and 2 lean. Had it happen before. Cleaned MAF sensor. Fixed it then. Gonna try that first.


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## christmas racing (Sep 1, 2010)

*Try this*

If that don't fix it have a shop some one YOU have used or trust to work on your truck do a fuel injector clean and TB clean on your engine 150.00 to 200.00 .Always do the little things first fuel injector cleaner from parts house . Don't get the cheap stuff get the good cleaner . Get a can of brake clean take off air filter tube . With engine off open TB spray brake clean in till it looks clean .When you crank your truck it will be hard to start and will run bad then clear up 30.00 to 75.00. Drive if that don't fix it you might need to tune it up cap rotor wires plugs fuel air filters 150.00to 175.00 .I hope this helps :cheers:


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## davidluster (Sep 16, 2008)

I think I fixed the problem. When I was changing the alternator I accidently pulled a vacuum hose loose. I reattached it and it reset the codes by disconnecting battery...THe CEL came on again so I went to Oreilly and cleared it again with the scanner. The light has now been off for about 10 days. 

Thanks everyone for the help.


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## pwrstrkr (Oct 5, 2010)

glad to see you got your truck fixed...my dad has owned a starter, alternator and battery shop for almost 30 years so i grew up working on trucks...i was just wondering where you paid $300 for an alternator if you dont mind me asking? cause that is hella expensive for what i can rebuild one for,


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## davidluster (Sep 16, 2008)

That $300 was for battery, alternator and a few other litlte things I tried to get the CEL light off....the alt was only about half of that.


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