Alternator or battery?

heyjewel

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Morning all. So my LS been in garage for a year. Brought it back out last week. Running great for a week though cranking seemed a little slow. Then I went in store, came out, car started, I pulled into lane and began to cross street and car stalled and would not crank at all. not even enuf juice left to put up the driver's window. So I called AAA and am still, 3 days later, waiting for them to call back. So I got a jump and went straight to auto store. They load tested the battery and it was 12.7 v. Good? Bad? Came home. Put on charger for several hours. 12.7v still but no load. Car still started.
I'm thinking alternator because car seemed to crank slower and slower over a few days. figure battery not getting charged? Any bets? Any test for alternator I can do?
I think I recall a post here years ago said if car wont start do this not that with key/ignition.
 
Why guess? Check the battery voltage while the engine is running.
14.0 to 14.4 Volts, it's charging well.
13.8 to 14.0 Volts, it's probably okay.
< 13.8 V, its not really charging.
 
Why guess? Check the battery voltage while the engine is running.
14.0 to 14.4 Volts, it's charging well.
13.8 to 14.0 Volts, it's probably okay.
< 13.8 V, its not really charging.
I will check this thanks.
 
Why guess? Check the battery voltage while the engine is running.
14.0 to 14.4 Volts, it's charging well.
13.8 to 14.0 Volts, it's probably okay.
< 13.8 V, its not really charging.
This is exactly the info I wanted. Thanks. And the loser is the battery. 14.5 volts while running. Battery is losing voltage overnight - from 12.7 down to 12 in AM. Upper 20s temps.

I do also wonder if there's a loose connection somewhere. To explain why it starts perfectly well for several days then bang dies after another successful start. And it was really dead. Then car has started fine again for couple days.
 
This is exactly the info I wanted. Thanks. And the loser is the battery. 14.5 volts while running. Battery is losing voltage overnight - from 12.7 down to 12 in AM. Upper 20s temps.

I do also wonder if there's a loose connection somewhere. To explain why it starts perfectly well for several days then bang dies after another successful start. And it was really dead. Then car has started fine again for couple days.
You may have an intermittent parasitic drain.
 
You may have a bad cell in the battery, which is causing your demon. Check the water level inside the cells. If you can see the plates, that's not good.

Check the sticker on the side of the battery... for the manufacture date. Anything over 7 years old is probably sketchy.

Aftermarket battery, or OEM Motorcraft? The high dollar Motorcraft usually lasts for 9 years.

Is the issue temperature dependent. Worse in colder temps?
 
You may have a bad cell in the battery, which is causing your demon. Check the water level inside the cells. If you can see the plates, that's not good.

Check the sticker on the side of the battery... for the manufacture date. Anything over 7 years old is probably sketchy.

Aftermarket battery, or OEM Motorcraft? The high dollar Motorcraft usually lasts for 9 years.

Is the issue temperature dependent. Worse in colder temps?
Motorcraft battery. Sealed. I'll have to check the date. Have only tested it in cold weather.
You may have an intermittent parasitic drain.
When u mentioned this, I searched webfor it. Found a pretty good description of a mech finding and fixing one of these. Here: 'Bright Idea' For Short Detection | MOTOR

I follow what he's doing except for measuring voltage drop across a fuse.
 
...I follow what he's doing except for measuring voltage drop across a fuse.
I didn't watch the video...
Measuring voltage drop across a fuse is a good way to tell if any current is running through that fuse. You don't know the resistance of the fuse, so you can't really tell how much, but any that you can measure is probably too much. The reason to do it this way is that you don't have to break (open) the circuit to check for current, so you don't wind up waking up modules and having to wait for them to sleep again to get a valid reading.
 
As long as alternator is charging between 12 and 14 it is ok. On my mark viii needing a battery after 7 years. New battery installed. After sitting for 2 or 3 days s battery dead. Took back to dealer they tested and said it was alternator. I asked what was the reading they responded 12.7.they were unaware that I was fleet director for 900 school buses. They kept insisting that it was alternator when I informed them the battery was bad and reluctantly replaced with another new battery. 3 years later no issues. After this I ended dealing with this company after 25 years. I just replaced tires on markviii and Navagator and let them know they lost a $1200. Sale plus oil changes twice a year for 3 vehicles.
 
As long as alternator is charging between 12 and 14 it is ok. On my mark viii needing a battery after 7 years. New battery installed. After sitting for 2 or 3 days s battery dead. Took back to dealer they tested and said it was alternator. I asked what was the reading they responded 12.7.they were unaware that I was fleet director for 900 school buses. They kept insisting that it was alternator when I informed them the battery was bad and reluctantly replaced with another new battery. 3 years later no issues. After this I ended dealing with this company after 25 years. I just replaced tires on markviii and Navagator and let them know they lost a $1200. Sale plus oil changes twice a year for 3 vehicles.
The alternator is not really charging the battery if the voltage is below 13V while running!
 
Wrong! If what you said is true how come my battery is always charged??? And this is on a car that is driven perhaps once a week???
 
Wrong! If what you said is true how come my battery is always charged??? And this is on a car that is driven perhaps once a week???
12.0V is a pretty discharged battery. 12.6 is charged, but the alternator voltage have to be higher to flow current into the battery. Typical charging voltage is 14.0 to 14.5. 13.8 is a minimum to charge a 12V lead acid battery.
I feel like you will not be convinced. I ask others that view this thread not to take my word on it. Do your own research.
 
The alternator is not really charging the battery if the voltage is below 13V while running!
I was gone for a week. Got back today. I had given the battery a solid charge before I left. Car in metal building. Temps in mid 20s. Checked batt voltage today - 11.7 Turned the key and it started but slowly. Obvious low on juice. So I'm heading to local auto parts store for a new one. For $189.00 Thanks for your advice. Always appreciated.
 
I was gone for a week. Got back today. I had given the battery a solid charge before I left. Car in metal building. Temps in mid 20s. Checked batt voltage today - 11.7 Turned the key and it started but slowly. Obvious low on juice. So I'm heading to local auto parts store for a new one. For $189.00 Thanks for your advice. Always appreciated.
Gonna get motorcraft. Less money. 750Amp.
 
12.0V is a pretty discharged battery. 12.6 is charged, but the alternator voltage have to be higher to flow current into the battery. Typical charging voltage is 14.0 to 14.5. 13.8 is a minimum to charge a 12V lead acid battery.
I feel like you will not be convinced. I ask others that view this thread not to take my word on it. Do your own research.
 
Not talking about battery power Or volts in battery but the amount of current the alternator is pushing to battery again if alternator is putting 12-14 to battery there is no problem with alternator
 
Not talking about battery power Or volts in battery but the amount of current the alternator is pushing to battery again if alternator is putting 12-14 to battery there is no problem with alternator
This is the least sensible sentence I have read in a long time...
 
12.0V is a pretty discharged battery. 12.6 is charged, but the alternator voltage have to be higher to flow current into the battery. Typical charging voltage is 14.0 to 14.5. 13.8 is a minimum to charge a 12V lead acid battery.
I feel like you will not be convinced. I ask others that view this thread not to take my word on it. Do your own research.
Yup. Charging voltage should be 1.5 volts over battery voltage
 
Morning all. So my LS been in garage for a year. Brought it back out last week. Running great for a week though cranking seemed a little slow. Then I went in store, came out, car started, I pulled into lane and began to cross street and car stalled and would not crank at all. not even enuf juice left to put up the driver's window. So I called AAA and am still, 3 days later, waiting for them to call back. So I got a jump and went straight to auto store. They load tested the battery and it was 12.7 v. Good? Bad? Came home. Put on charger for several hours. 12.7v still but no load. Car still started.
I'm thinking alternator because car seemed to crank slower and slower over a few days. figure battery not getting charged? Any bets? Any test for alternator I can do?
I think I recall a post here years ago said if car wont start do this not that with key/ignition.
 
My response here may be 'after the fact' but here it is: The basic problem is a weak/worn-out battery and should be replaced.. Despite the fact that the alternator does appear to be charging this faulty battery, it is getting only a 'surface charge' and that doesn't store much battery starting energy. Thus it may work from time to time but then again it may not and leave you stranded - - as you have reported. In addition, there is a constant 'parasitic' current drain on the battery even though the car sitting unused. How do I know? Left car in my hangar while away on a 30-day trip. Loaded luggage in trunk then tried to start engine. Nothing! Had to unload luggage and get jump start and then all was well. At home I measured the parasitic drain and AIR it was about 0.7 ampere (700 milliamps) Take this value, multiply it by the number of hours in a month and the result is roughly the ampere-hours drained. For me that was about 250 ampere-hours - enough to kill or weaken the battery when I hit the starter. And FWIW the alternator should be putting out roughly 13.8 volts or so.
 
Might I suggest also that if the car has been sitting for a year, that it's possible that the starter connections may be corroded.

That could cause a parasitic drain along with poor starter performance.
 
Battery terminal corrosion will increase overall circuit resistance and will reduce parasitic current drain and any other component (like starter) will receive much less energy.
 
I didn't say battery terminal corrosion. I said starter terminal corrosion. :rolleyes:

I'll bet that if Heyjewel crawls under the car, he will see green and/or white powder (crust) on the starter terminals.

Again... since the car has been sitting for a year, (possibly in a damp garage), this may be an issue. He DID say the car was in a metal building for a year.

 
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@heyjewel

Get your new battery and get some battery terminal cleaner. Spray the connections at the starter (with the battery disconnected), then hit the starter terminals with a wire brush (toothbrush sized).

Loosen the starter connections and scrub all the nuts and studs on the starter. At this point you would also want some "battery protector" spray to prevent further corrosion.

Then... reconnect your new Motorcraft battery, and spray the battery protector on the terminals. You may want to get one of those battery terminal brushes too, since the terminals sometimes have a film on them.
 
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