Not holding charge. Any ideas?

5.02GO · Jun 18, 2005

Summary:

A friend called today and explained that his battery would not hold a charge. He said that Autozone had checked his alternator and it was good to go. His battery is about 3 months old from walmart.

Symptoms:

He said that he can charge or jump his car to get it going and that it would run for a while then it would go dead. He would get a "battery" light on in the instrument cluster.

Model:

1992 Mustang GT. Minor mods. All motor. Underdrive pulleys. I believe its a 130 amp alternator. I am not positive on the amperage, just KNOW its not stock or factory.

I have ford prints and ford shop manual. According to the prints, there is a fuse on the yellow with white stripe wire. Unable to locate and do a continuity test.

Any ideas where this fuse might be located? Anyone experience this problem befor?

I dont really trust autozones "testing" myself. Alternator could be bad.

thanks......

stang22 · Jun 18, 2005

I would have AutoZone do a load test on the battery. Double check all of your grounds as well. Bad grounds equal no charge.

Tim

04sleeper · Jun 18, 2005

Do a quick check with a 12 volt light tester and see if the excitor wire is getting power to the alternator. It is a small white/black stripe wire comming from the plug with 2 bigger black/orange stripe wires.
Also test the voltage at the back of the alternator and at the battery when the car is running.
This should help determine where to go from there.

5.02GO · Jun 18, 2005

stang22 said:
I would have AutoZone do a load test on the battery. Double check all of your grounds as well. Bad grounds equal no charge.

Tim

Grounds are good.

Load test......Dont they do that when they test? Or do they just do a resistance check?

I'm obviously not an autozone fan.

txstang84 · Jun 18, 2005

if they're only testing the alternator, they won't do a load test-but try this:

with the car running take the neg batt cable off, turn on the lights, if the lights come on and the idle drops a little bit (but doesn't die) the alt should be good...the battery may have a dead cell which will keep if from maintaining a full charge

5.02GO · Jun 18, 2005

txstang84 said:
if they're only testing the alternator, they won't do a load test-but try this:

with the car running take the neg batt cable off, turn on the lights, if the lights come on and the idle drops a little bit (but doesn't die) the alt should be good...the battery may have a dead cell which will keep if from maintaining a full charge

I asked him about testing for dead cells in the battery. He did not have a tester.

Thats a good idea though about the lights. We'll try that tomorrow.

thanks.

giddyup306 · Jun 18, 2005

txstang84 said:
if they're only testing the alternator, they won't do a load test-but try this:

with the car running take the neg batt cable off, turn on the lights, if the lights come on and the idle drops a little bit (but doesn't die) the alt should be good...the battery may have a dead cell which will keep if from maintaining a full charge

That worked good with the old generators...however with all the electronics you can create a spike voltage and untimately fry components such as the computer. I'd ground the tab on the back of the alternator and make sure your reg is working (using a DVOM the voltage should go up). IF that works okay do a quick change on the battery and do a load test. While cranking make sure that the voltage does not go below 9.6V. In warmer climates you can get away with less. If it fails this there is probably a shorted cell and take it back to wall mart. Also make sure that your terminals are CLEAN! PLus if there is excessive resistance on the power or ground side (no more than .03V) if will not chrge. Do a voltage drop test to find this out. Also remember that a fully charged battery will have app. 12.6V fully charged.

Mike

bobbyd · Jun 18, 2005

txstang84 said:
if they're only testing the alternator, they won't do a load test-but try this:

with the car running take the neg batt cable off, turn on the lights, if the lights come on and the idle drops a little bit (but doesn't die) the alt should be good...the battery may have a dead cell which will keep if from maintaining a full charge

what if the idle doesnt drop and stays the same?

txstang84 · Jun 18, 2005

giddyup306 said:
That worked good with the old generators...however with all the electronics you can create a spike voltage and untimately fry components such as the computer. I'd ground the tab on the back of the alternator and make sure your reg is working (using a DVOM the voltage should go up). IF that works okay do a quick change on the battery and do a load test. While cranking make sure that the voltage does not go below 9.6V. In warmer climates you can get away with less. If it fails this there is probably a shorted cell and take it back to wall mart. Also make sure that your terminals are CLEAN! PLus if there is excessive resistance on the power or ground side (no more than .03V) if will not chrge. Do a voltage drop test to find this out. Also remember that a fully charged battery will have app. 12.6V fully charged.

Mike

as far as the idle drop, if your idle doesn't drop at all, then your charging system is in good shape...the only reason i mention the idle drop is based on the slight loss of volts and the extra load put on the engine by the alt.

Now about the voltage spikes...ok, you're right, voltage spikes can happen-if your VR is on the fritz then yes, you might have to worry about that...if i had gastrointestinal problems, pigs might fly from my a$$. The biggest volt spike you will more than likely see is 16v...and since the computer has a VR in the circuitry that prevents voltage from exceeding 12v for that very purpose, i'm betting you'll never know the diff

giddyup306 · Jun 18, 2005

txstang84 said:
i'm betting you'll never know the diff

No need to get pissy.

txstang84 · Jun 18, 2005

giddyup306 said:
No need to get pissy.

not pissy, no harsh feelings, just trying to keep reality in ck

giddyup306 · Jun 18, 2005

None taken.

HISSIN50 · Jun 19, 2005

Mike (Giddy Up) is ABSOLUTELY correct about the voltage spike. If someone wants to do that stuff to their own car fine, but dont lead other people to think it is ok.

Just because someone stands in a puddle during an electrical storm and does not get electricuted does not mean that person should advocate it being safe.

Why take any chance when there are other means to do the testing. For people with a lesser understanding of electrical systems than GU and Tx, they might think it is not only 'ok' but even acceptable to perform such a test. I personally would never do that test. That is just my personal opinion though.

As for the pigs, well no comment. There are other forums for that sort of issue.

I do believe in saying to each his/her own, but I dont want to see people taking a chance on frying anything when they dont have to take that chance. No disrespect intended toward anyone - this is just my opinion.

87mustang347 · Jun 19, 2005

maybe he doesnt have enough grounds. my car did the same thing and i added one more ground from the block to the frame and the battery hold its charge everytime now

5.0_Gil_89 · Jun 19, 2005

If your alt is good, and your battery it's the wire that runs from your light (batt light in dash). Their is a fuseable link in there. If it's blown the alt will not charge, the fuseable link will be burn or really swollen. Oh! back track, when he turns the key on does that batt light in the cluster come key on...do not start it. If the batt light doesn't come on like normal when the key is on then it's that fuseable link. If the light does come on then it's prolly the alt. Check all of your battery cables, and also to the starter. If I was you when you do fix the problem run another ground strap from the frame to the engine. Don't rely on the one coming from the back of the engine to the fire wall. A good ground cable can be made from stereo monster cable with 1/2 hole sized ends. Ford as you know has problems with grounds, especially a car that is pushing 20 yrs. Hope this helps, sorry for the confusion. Just make sure that the light illuminates with just the key on, if not start pulling the dash apart and trace that batt light wire to the fuseable link. USA!!!!!!

giddyup306 · Jun 19, 2005

HISSIN50 said:
Mike (Giddy Up) is ABSOLUTELY correct about the voltage spike. If someone wants to do that stuff to their own car fine, but dont lead other people to think it is ok.

Just because someone stands in a puddle during an electrical storm and does not get electricuted does not mean that person should advocate it being safe.

Why take any chance when there are other means to do the testing. For people with a lesser understanding of electrical systems than GU and Tx, they might think it is not only 'ok' but even acceptable to perform such a test. I personally would never do that test. That is just my personal opinion though.

As for the pigs, well no comment. There are other forums for that sort of issue.

I do believe in saying to each his/her own, but I dont want to see people taking a chance on frying anything when they dont have to take that chance. No disrespect intended toward anyone - this is just my opinion.

Why thank you JT. +1 for Hissin5.0

Not holding charge. Any ideas?

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