Battery or Alternator...Please Help!

[Awesome96XLT]

Hey guys, so I need some advice diagnosing this problem.

There is a lot of writing so I am just going to bold the key points.

About a week ago, I started to notice that my battery was reading at 11.5 volts consistently. I ignored it, as the truck was running fine. Yesterday, the truck died as I was idling on the street. The lights dimmed, some beeping started to occur, the battery light came on, and the car died as I was idling on drive. I got it jumped, then 5 minutes later, it died as I was preparing to turn right at a stop sign. The time between the first and second jump, my battery was reading 9 or 10 volts.

3 more things:

1. I helped a guy jump his car two weeks ago and it took FOREVER to get his car to take a charge, so my cables were hooked up to his for a good 15 or 20 minutes...could this have drained my battery beyond its ability for the alternator to recharge it?

2. When I got my oil change a month ago, the mechanic told me that I have serpentine belt tensioner issues that is causing intermitant check engine lights, but I just jumped the car and checked the serpentine belt, and the belt is running fine and smoothly...

3. I thought I had the problem nailed as an alternator problem, but I just hooked up my multimeter to my car and jumped it. It would idle around 11.5 volts but when I revved the engine past 4500 rpm, it would jump up to 13v, then as I let off the gas, it would go back down to 11.5.

So....I am not sure if it is an alternator problem, as I originally thoughts, because of the higher voltage upon revving.....but at the same time, I am not sure if it is just a battery problem either?

Please help and thanks alot in advance!

 

[SoNic67]

You have a dead alternator originally - the reading with engine running at 1000 rpm should be a stable 14.2V +/- 0.2V.
You just run the battery dead ignoring that voltage warning. If is old enough, and in freezing weather, that could kill it.
PS: You can KILL an alternator trying to charge a battery that was discharged down to 9V with the alternator. I seldom "give a jump" to people because I had one of my alternators fried like that - true it was older, but anyway...

 

[koda2000]

a fully charged battery should read 12.6 volts static. with the vehicle ildling you should be seeing in the 13.6-14.6 volt range on a multi-meter. how old is your battery? can you charge your battery and get it load tested? it's most likely your aternator, but it could also be the battery if it's shorting out internally.

 

[Awesome96XLT]

Thanks for your help... Currently, my battery reads:

11.4 v (will not start car)

11.55 v (when car is jumped and idling)

13.2 v (when I rev up to 4000 rpm)

Normally, my battery reads around 14 v. And the only reason why I ignored it earlier this week was because I thought it was a problem with my stereo system, because that was the unit telling me the voltage earlier this week.

What is getting it load tested mean? So is it pretty much sure that my alternator is fried? I was thinking that it may be ok, since the voltage rises when I rev it. Maybe the battery is just so kaput that it wont hold a charge given to it by the alternator? Any opinions?

Thanks again guys!

 

[koda2000]

Thanks for your help... Currently, my battery reads:

11.4 v (will not start car)

11.55 v (when car is jumped and idling)

13.2 v (when I rev up to 4000 rpm)

Normally, my battery reads around 14 v. And the only reason why I ignored it earlier this week was because I thought it was a problem with my stereo system, because that was the unit telling me the voltage earlier this week.

What is getting it load tested mean? So is it pretty much sure that my alternator is fried? I was thinking that it may be ok, since the voltage rises when I rev it. Maybe the battery is just so kaput that it wont hold a charge given to it by the alternator? Any opinions?

Thanks again guys!

Voltage doesn't mean much. amps do. the auto parts store has a test machine that puts a load on the battery (via resistance) to see how it responds.

 

[buckwill]

your alt is not fried,, if it was you would not get any voltage,, most likely you have a voltage regulator problem, could also be a brush problem or combination of both,, if you ahave a battery goin bad an makes the alternator charge constantly it will usually ressult in alternater failure,, automotive alternaters are just not equipped to handle constant charging losads,,, its a pretty fair bet u can count on needing to replace battery and pretty sure the alternater,,u can rebuild the alt easy but check prices and compare reman vs kits, dont forget bearings, even with a dead battery your charging voltage will,,or has been for years been 13.8 to 14.2,, if your battery is faailing,, it will still be tween those numbers running, but if it consistantly falls lower then your voltage regulater has failed,, buck

 

[Awesome96XLT]

Thanks for your guys' help. My battery is less than 2 years old. If it is around 11.4 v off, can I buy a trickle charger to charge it or do I have to buy a new battery.

 

[koda2000]

a small trickle charger is not suitable for charging a dead battery. the auto parts store can charge it for you for free (and test it) but be prepared to leave it there for a 45 mins up to a couple of hours. if your battery is bad, and under 2 years old, you should be able to get it replaced under warranty for free. if the battery is okay, get your alternator tested as it's most likely bad. you probably killed it jumping that other car. buckwill is incorrect in saying that you would get no voltage out of a bad alternator. it depends what's wrong with it. the auto parts store's machine can tell you exactly what the problem is.

 

[96eb96]

I think the alt is on its way out. A Simple test is turning on all accessories at idle and measuring voltage. If you are under 13.8 or so you need one.

At 4000 RPM it is struggling to charge the battery at 13.2. If you want to be 100% sure have the battery charged, tested and do the above test. There is a remote chance of a dead short in the battery, so you may want to check that. If that is the case the alt is likely ruined.

I can assure you with your numbers if you goto a parts store and get the alt tested they will tell you its bad.

Make sure the batt is FULLY charged and confirmed working before installing your new alternator. Parts stores(even walmart!) will be happy to charge and test the batt. Many alternators are warrantied and replaced because of bad batteries. The alternator is designed to top off the battery after idling with your accessories and lights for 10 minutes. If you replace the batt, I suggest a Motorcraft 850CCA unit from a Ford dealer. They are not much more than Walmart, and it is a great battery.

 

[deweyville65]

i think you need more than a trickle charger. Take the battery somewhere and have it charged,then read your voltages with the engine running. You should have 13.6 volts minimum with the engine running, 12.5 or better with it shut off. You can do what I call a poor mans load test. run the engine for at least 15 minutes, shut off engine, check voltage. with engine shut off turn on headlights high beam preferably. check voltage 12 minimum. Leave headlights on for 10 minutes then check voltage, minimum 10.5 to 11 volts. Any less voltage, your battery is done for. These are ONLY ball park figures. What you are looking for is how much the battery will hold or not. The engine should start with a minimum of 10.5 volts, but it may not, especially if the battery is marginal. Also, in cold weather, before you try to start the engine, turn your lights on for a few seconds, helps to "excite" the battery. A trick we used years ago to help start diesel engines in cold weather, before computerized fuel systems.

 

[Awesome96XLT]

Alright guys, just did the diagnostic test at the local shop. The slip says I need to get a new battery, but I haven't brought in the car yet to test the alternator...I will do that tomorrow.

Anyway, the results of the test are....

Rated: 850 CCA
Measured: ---
Voltage: 12.37
Elapsed: 1 Hour
Amp Hours: 25

tomorrow I will get the alternator tested...

 

[1996BLKBauer]

As I am sure you have already found out. Your Alternator is most likely dead, or dying, if it has been leaking AC voltage into your battery for a long enough time, that is most likely the reason the battery is bad as well, before buying a new battery, check/replace the alternator. Regular changing voltage when at idle is around 14.6, also you should have no need to go above 2000rpms to get the max output for the alt. When I do a load test in the shop, the manual says to do the test at 1200-1500rpms.

 

[SoNic67]

Don't get a new battery yet. Charge it with a battery charger first and then test it at the store.
And yes, the alternator should output 14.2V. I you read 13V means that a diode is busted and pushes Alternative Current into the battery instead of Direct Current.

 

[96eb96]

Voltage: 12.37
Elapsed: 1 Hour
Amp Hours: 25

Should be no less that 12.8-.9V after a charge like that.

 

[96eb96]

Don't get a new battery yet. Charge it with a battery charger first and then test it at the store.
And yes, the alternator should output 14.2V. I you read 13V means that a diode is busted and pushes Alternative Current into the battery instead of Direct Current.

The slip said it was charging for an hour - if that is the case the battery is toast with his numbers.

 

[koda2000]

a small trickle charger is not suitable for charging a dead battery. the auto parts store can charge it for you for free (and test it) but be prepared to leave it there for a 45 mins up to a couple of hours. if your battery is bad, and under 2 years old, you should be able to get it replaced under warranty for free. if the battery is okay, get your alternator tested as it's most likely bad. you probably killed it jumping that other car. buckwill is incorrect in saying that you would get no voltage out of a bad alternator. it depends what's wrong with it. the auto parts store's machine can tell you exactly what the problem is.

 

[russosborne]

definitely dead battery at this point. Most likely a bad alternator took it out. However, a slipping belt could also cause some of this. You did mention that the shop said that the tensioner pulley was questionable. Depending on the mileage on yours, it might be cheap insurance to do all three things.
Oh, just in case. Never disconnect the alternator while the engine is running. That is an old wive's tale test that WILL kill the alt. I know you haven't said anything about doing that, just wanting to make sure you or anyone else doesn't try.
Russ

 

[koda2000]

definitely dead battery at this point. Most likely a bad alternator took it out. However, a slipping belt could also cause some of this. You did mention that the shop said that the tensioner pulley was questionable. Depending on the mileage on yours, it might be cheap insurance to do all three things.
Oh, just in case. Never disconnect the alternator while the engine is running. That is an old wive's tale test that WILL kill the alt. I know you haven't said anything about doing that, just wanting to make sure you or anyone else doesn't try.
Russ

yeah, doing that can also fry your PCM with a voltage spike. don't do it.

 

[96eb96]

definitely dead battery at this point. Most likely a bad alternator took it out. However, a slipping belt could also cause some of this. You did mention that the shop said that the tensioner pulley was questionable. Depending on the mileage on yours, it might be cheap insurance to do all three things.
Oh, just in case. Never disconnect the alternator while the engine is running. That is an old wive's tale test that WILL kill the alt. I know you haven't said anything about doing that, just wanting to make sure you or anyone else doesn't try.
Russ

The idler and tensioner pulley on mid-90s exes should be replaced regardless!They are known to fail on these trucks. This goes for anyone reading the thread. When it fails you will lose power steering and overheat your truck.

 

[Awesome96XLT]

Thanks for everyone's help. So I brought the car back to the auto parts store and they retested the battery again, because they needed to charge it to test the alternator......

I guess now they say the battery is good? I told them to check it again twice, and they say its good. They charged it for an hour and said I could have it back. The alternator, however, is bad.....So I bought a new alternator and installed it yesterday. I am wary of using this battery that was at once bad but now is good, with a new alternator, but there is a lifetime warranty on the alternator, so I guess it is ok...

Thanks again everyone!