Alternator Working Intermittently

[ZGrand]

2006 Mustang GT Premium convertible 5-speed manual with 75K miles. I bought this car in 2015, and it has been trouble free (knock on wood). For various reasons, it sat for about three weeks recently, and when I cranked it up to go for a ride, I got the dreaded "Check Charging System" message. Sometimes when I crank it I get the message, and sometimes I don't. When I do, the alternator check function on my battery charger says "Bad", when I don't get the message, the alternator check says "good". So the alternator is working Intermittently.

I will take it to my mechanic who is about 8 miles away. Here's my question. If the alternator is not working, how far can I drive it on a fully charged battery? Will it likely make 8 miles? Thanks.

 

[ZGrand]

 

[DieHarder]

Before taking it in I'd recommend cleaning the alternator leads, grounds and battery cables. If you have a multimeter you might want to check the battery voltage across the pos/neg with the engine running. If voltage isn't above 14v likely your grounds need cleaning or you could have a bad alternator but the intermittent nature of the problem I'd call the alternator good until it fails completely. If you do pull it take it to an alternator shop; not an auto parts store. They don't have the right equipment to test it properly. Cabling is getting old in these cars so corrosion/oxidation builds up which increases the resistance and causes all sorts of electrical problems. If output across the battery is less than 14.3v I'd suspect cabling and/or grounds. You can still get replacement battery cables but they'll likely run around $100. Be sure to get OEM/autocraft. If it were me I'd start w/testing and cleaning ground connections.

 

[86GT351]

Sounds more like a possible bad cell in the battery. Have the battery professionally load tested.

 

[GriffX]

FYI: You can open the Motorcraft batteries and add some distilled water if cells are low. There is a plastic "thing" inside and the acid must touch it (you see it immediately because the light reflection will change when the acid touches it)

PS: Please wear googles at least and gloves.

 

[JC SSP]

If you're going to refill a battery with water, I suggest distilled water. Please wear gloves and goggles too...

 

[ZGrand]

Thanks for the replies. Every time I crank it now it's giving me the "Check Charging System" message, and my voltmeter reads 12.2 volts across the battery cables. I disconnected the negative battery cable with the engine running and sure enough it died, so the alternator is not charging. Hopefully I can get the 8 miles to my mechanic on battery power.

 

[ZGrand]

New alternator installed and all is right with the world again.

 

[JC SSP]

Stock replacement or upgraded?

 

[ZGrand]

Stock. I know they can be problematic, but the first one lasted 18 years. Maybe I'll be lucky again.

 

[Sone97]

You've already been given great advice. My only recommendation (if you can swing it somehow) would be ditch the lead/acid and go AGM (red optima) for the battery.

Nice car BTW. I have the same thing (only hardtop with dove interior and factory "18 fan blades) The dove interior is the drawback for me (it just catches the dirt if you don't keep up on it) I picked my car up in 2018 with 59k on it. First thing to fail was the interstate battery. Instantly went out and got a red top along with replacing the alternator with a PA performance unit. That was seven years ago, zero problems with the alternator (always pegged at 14 plus volts on the autometer) I am however on my second redtop in that same amount of time.

They can be hit or miss, but generally are solid and worth it. I had a red top Optima last a decade (from '95 to 2005) in a daily driven Chevelle. Since they moved production south of the border, that kind of longevity was cut in half or so. I do love the Windveil Blue Metallic (reason I bought the car along with the TR3650) I've seen similar or close on older Camaros & Mustangs. It's just the perfect color on these cars.

 

[ZGrand]

Good advice on the battery. Sorry to hear that Optima batteries aren't as good as they used to be. I have a yellow top Optima in my 2001 GMC Sierra. You won't believe this (but I swear it's true) -- I installed it 9/24/07. Still working after 17 years!! Although it's getting a little weak now and really should be replaced before I get stranded somewhere.

 

[07 Boss]

I have a brand new, not rebuilt, stock replacement alternator on the shelf. Before I put it in I got hold of a 2010 alternator and used that instead. Before that I went through 5 alternators. This one has been running strong for years.

 

[DiMora]

The stock alternators 2005-2009 are garbage…and the clutched pulleys like to fail as well (it’s a one-way clutch on the stick cars). I also went through 4-5 stick alternators before I bought 2010 unit.

Always upgrade to the 2010 alternator:

Ford Mustang / GT Bullitt Alternator (Motorcraft GL950) (2010):
P/N: (9R3Z-10346–B)

Also, I will second that the Optima batteries have gone downhill. It’s not so much that the batteries suck, it’s that the company sucks, and getting warranty swap takes a pint of blood, a blursed chicken’s foot, and a lock of hair from your first-born.

Instead, I like the Interstate no-spill AGM batteries.

 

[GriffX]

Looks like the alternators up to 2009 were produced from Wei Global China, I changed it to a 2010 Denso.
The clutch at the Wei was INA Germany printed on, made some horrible noises and I found that INA Germany is not INA Made in Germany, it is China too.
I don't give any recommendations for batteries or tires anymore. They change the ingredients almost every year. So many battery producers are gone in Europe, I must admit I buy cheap batteries. I have a mixtech right now.

I once tried to get a warranty swap of a crazy expensive "Mercedes" battery, yea, "we must check your car first on your costs" .....WTF

 

[Windstang]

My original stock alternator died last year and I replaced it with a 2010 and just made the power cable connector larger and all good. I just use Costco batteries and replace every 5 years or so. I took the original alternator apart to inspect it - brushes looked worn of course but not horrible. I bought a rebuild kit which was basically a new regulator with brushes and bearings. I cleaned the commutator and installed the new regulator and figured I'd have a spare. I took the alternator to a local parts place and it showed NFG so I took it apart again. I looked for other problems and it 'looks like' some of the soldered diode connections have failed due to cold solder joints (perhaps). I tried re-soldering them but they must have used a higher melting point solder or my soldering gun isn't getting hot enough but I couldn't get the solder to flow and nicely re-solder the diode connections. I play with it occasionally and may take it back to testing if I can solder it properly - but as someone said - don't take it to the local parts store so I may have a nice boat anchor! The new 2010 alternator has been working great. I don't drive it over the winter and connect an automatic trickle charger to keep the battery happy.

 

[ReddComett]

06 GT owner here, and found the solution to be having the alternator rebuilt. After experiencing charging issues with no light myself, I tested everything under the sun on advice from various forums on old posts. Commonly, people report that aftermarket units do not work, and I had the same experience even with supposedly new units. I eventually had it rebuilt at a local electronics repair shop. This solved the issue, and i have no further issues after 2,000 miles. I just wanted to stick this on the end for others in the future who struggled to find a good answer like I did.

 

[DieHarder]

06 GT owner here, and found the solution to be having the alternator rebuilt. After experiencing charging issues with no light myself, I tested everything under the sun on advice from various forums on old posts. Commonly, people report that aftermarket units do not work, and I had the same experience even with supposedly new units. I eventually had it rebuilt at a local electronics repair shop. This solved the issue, and i have no further issues after 2,000 miles. I just wanted to stick this on the end for others in the future who struggled to find a good answer like I did.

What did it cost to rebuild?

 

[Pentalab]

On my 2010 GT, same oem 2010 alternator....runs like a top. I measure 14.75 vdc (using a calibrated fluke 87 DVM) right at the battery terminals....idling. The next morning the battery reads 12.4 vdc..with eng OFF. This is normal. If you are not seeing 14 + vdc at the battery with eng idling, (or directly from the alternator), either cables have bad connections or alternator is toast.

Another easy test is to switch the DVM to read AC voltage. You should see next to nothing for AC volts, mere mv at most. If you are seeing a substantial amount of AC voltage, one of more diodes inside the alternator have failed shorted.....which will pump a raw AC component into the battery. And batteries don't like AC voltage, that will slowly destroy a battery over just a few months.

 

[Autokyrios]

Stock. I know they can be problematic, but the first one lasted 18 years. Maybe I'll be lucky again.

Jebus christine....18 years? Give that thing a ceremony and recycle it.
Don't mess with the headache or guessing, just get a new battery. Replace it with a good AGM battery. May not be all your problems, but definitely would eliminate a lot.