Charging problem

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So early last week, my wife reported that the "Battery" light came on in our '05 Impala. The light turned on and turned off, but that it had turned on at least once (she doesn't know/can't remember if it had come on before). I tested the battery and it tested fine- 12.4V. I turned on the car and turn on the lights, A/C, and radio and tested the alternator and it came back low- 13.5V. I took that as conclusive that it was the alternator going out and so I bought a replacement alternator (link to alternator purchased) and installed it Sunday. Sunday: Install went smooth, no real issues. After getting the new alternator installed, I made sure the belt was routed properly and that it was taut, double-checked that the alternator was reconnected and started it back up. She fired over and ran as good as usual. Put the multi-meter back on it and the alternator was at 14.1, which was still a hair low but it flickered above 14.2 enough that I was fine with it. Let it run for about 90 seconds, with the A/C on, radio on, etc. Shut it down, waited 5 minutes, fired it back up again and all tested fine. Monday: No issues, it made it's daily 7.5 mile round trip excursion without complaints. Tuesday: Today, it fires up normally, but dies on my wife (battery light comes on, car dies) about 50 yards from her work. Fortunately, it was close enough to get it pushed there by her co-workers. She reports that the belt is still on and taut, it's still plugged in, etc, and everything is still good. I asked her if she tried to start it and she said no, so she goes to start it and it fires right back up again. Now, I haven't had a chance to look at it yet, but I'm not exactly sure where to look honestly. My first thought is a ground going bad, but I don't know for sure. I also noticed a little bit of bounce in the tensioner when the car was running, but I don't think that's the culprit here. Anyone have any ideas where I should start looking first? TIA!
 

JustN89

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Wouldn't the car have an issue starting if the battery was going bad? I'm not ruling it out, but it just seems weird to me that the battery tests fine and the car doesn't have any issues starting. I'll pull the battery though and take it to O'Reillys and get it tested with something other than my multi-meter.
 

JustN89

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I won't disagree with you there. I've been wanting to replace it for a while now, but it's actually been strangely reliable in the 3 years we've owned it. This is the first time it's failed to get to its destination. It's the 3400.
 
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Originally Posted by JustN89
Wouldn't the car have an issue starting if the battery was going bad? I'm not ruling it out, but it just seems weird to me that the battery tests fine and the car doesn't have any issues starting. I'll pull the battery though and take it to O'Reillys and get it tested with something other than my multi-meter.
Load test . Quick tip: Your multi-meter, hold it on both posts of the battery for 20 seconds to a little longer than that. If you get any rapid fluxuations in the voltage, you may have a cell going soft, or some other kind of short in your battery. Also look to see if the battery is bulging. Hot weather may be masking that it is having issue holding a charge, load test but if you have a cell that overflows when being charged usually accompanied by a bulge, and again look for the number to change quickly, say, from 12.62V to three or four other numbers quickly then back again within a second or two, leads steady on the battery.. then it is shot. It should be staying the same consistently. If O'Reilly can test it too, but they like to test a battery that just came out of a running car if you are testing that same battery, almost guaranteed to not be a valid test result.. load test.
 
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You need a load tester NOT a volt test with a multimeter. As stated above, battery can pass volt test but not load test which test the amp-acity of the battery. That is not saying that the alternator is good. The alternator can be weak also, that is why with new alt, the battery can be good for a little while longer.
 
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JustN89

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Thanks for the advice. I'll load test it this evening.
 
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Originally Posted by JustN89
Thanks for the advice. I'll load test it this evening.
14.1 is a good reading on the battery when car is running. Indicates charging alternator. Some say 14.2 .. this to the point where it depends on the temperature outside etc. 14.1 is fine and dandy. I always thought and was told 14.1. If your battery fails the load test you have your answer. What does the voltage say after it sits for.. an hour? 6? It should rest at 12.6V or north. 12.62, 12.78, 12.65, any of these is good.. Had plenty of batteries resting at 12.92V that were hiding issues.. load test.
 
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It's normal for the battery light to come on if the key is on but the engine is not turning. It really sounds like there is some other problem causing the car to stall out, since there was plenty of power in the battery to re-start. Many modern cars have a "smart charging system" that doesn't regulate to a constant voltage. You would want to see more than 13 while running with the headlights on.
 

JustN89

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Originally Posted by mk378
It really sounds like there is some other problem causing the car to stall out, since there was plenty of power in the battery to re-start.
I'm starting to think that this may be the problem. I'm wondering if she is recalling things backwards- instead of the battery light coming on and then the car stalling, I'm wondering if it didn't stall on her first and then the battery light came on due to the key still being in the "On" position. She did say that the stalling and light coming on was simultaneous. This would be a different problem altogether, of course.
 
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First , carefully disconnect the battery cables from the battery . Wash / clean / polish / neutralize acid on the cable ends and battery posts . Rinse . Check and replace the belt , if needed . Wash / clean / neutralize acid / rinse the top of the battery . Inspect cables and cable ends for corrosion damage . Even under the insulation . Grease up the cable ends and battery posts and re-attach . Check cable termination on the starter , alternator and " fuse block " . Check voltage ( engine off ) at the alternator , at the battery , at the starter ( if you can get to it ) . Write all this down . Start the engine and repeat the above . Write it down . Come back and share info .
 
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Originally Posted by JustN89
Originally Posted by mk378
It really sounds like there is some other problem causing the car to stall out, since there was plenty of power in the battery to re-start.
I'm starting to think that this may be the problem. I'm wondering if she is recalling things backwards- instead of the battery light coming on and then the car stalling, I'm wondering if it didn't stall on her first and then the battery light came on due to the key still being in the "On" position. She did say that the stalling and light coming on was simultaneous. This would be a different problem altogether, of course.
That would be the Impala/3400. lol.
 

JustN89

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Follow-Up: Performed load test and everything checked out fine. Sat at 11.2 V until I stopped the test, then went back to normal. Started the car and ran accessories, battery stayed in acceptable range. Other data collected- vacuum was 19.6 in/Hg at idle, 22 in/Hg at 3300 RPM. dipped to as low as 18.4 in/Hg at idle, but always recovered back to around 19.6. Long term fuel trim at idle was -13.3%, short term fuel trim at idle was 1.6%. At 3100 RPM, long term fuel trim was 2.3% and short term fuel trim was -0.8%**. It started up every time I tried, though a few times it did struggle a bit to start or catch its idle- may be pointing to a fuel problem. Fuel filter I know is good, but the pump is original (as far as I know). Any more ideas? Maybe it was just a fluke? **This data was collected with the car in park and me adjusting the throttle manually.

screen grab.PNG
 
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Take the battery cable ends completely apart & clean them.....It's impossible to clean GM side post terminals without removing the rubber sheath off the end of the cables.
 
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