My alternator may by dying again

[LordBritish]

I measured the battery voltage when idling and it was only 13.1 volts.
I understand that it should be around 14 volts.

I heard that 2010 OEM alternators will fit an 05GT.

Is that true?

TIA

 

[redfirepearlgt]

Place a load on the car like turning on the AC unit to maximum when you check that. The current demand should trigger the regulator to step up. As well place he meter so you can see it from inside the car and lightly raise the idle to about 1200-1300 and see if the voltage changes. 14vdc is a good number as long as you see voltage increase and decrease as demand on the charging system increases.

Also check the AC voltage. It should be virtually zero. Standard 0.250VAC or there about is acceptable. AC output above that is an indication of a shorted Diode in the full wave rectifier circuit on the alternator. There is a video addressing how to check for that in another thread pertaining to this topic. OR google "checking diodes on a Ford Alternator" and you should get plenty of hits on how to set your multimeter to the diode setting and perform this action. I won't go into forward and reverse bias theory of diodes. The video shows you enough to check it yourself.

Oh here it is - https://www.youtube.com/watch?v=xgikeXt91vM

 

[Dino Dino Bambino]

I measured the battery voltage when idling and it was only 13.1 volts.
I understand that it should be around 14 volts.

I heard that 2010 OEM alternators will fit an 05GT.

Is that true?

TIA

Yes it's true but since the cable socket is in a different location on the 2010 alternator, I'm not sure if the cable will reach without needing to extend it.
A battery voltage of 13.1 at idle (no accessories running) is probably due to a faulty regulator. If the diode test reveals little or no AC current leakage, you can just replace the regulator instead of replacing the whole alternator.

http://www.aspwholesale.com/alternator-rebuild-kits/ford.html?page=all

 

[LordBritish]

The AC voltage was 0.027 (measured from battery posts).

Alternator got up to 14 volts DC when under load.

Hmm, seems that may be Alternator is OK.

Perhaps battery just needs to be replaced. It's voltage this morning was 10.9 volts DC.

After jump starting the car and driving it around, it was 13 volts.

It seems like the battery loses charge fast while just doing nothing.

 

[Pentalab]

The AC voltage was 0.027 (measured from battery posts).

Alternator got up to 14 volts DC when under load.

Hmm, seems that may be Alternator is OK.

Perhaps battery just needs to be replaced. It's voltage this morning was 10.9 volts DC.

After jump starting the car and driving it around, it was 13 volts.

It seems like the battery loses charge fast while just doing nothing.

Your alternator + regulator are fine..... but your battery is toast.
Either the battery is toast....or there is something in the car that is still putting a tiny bit of a load on the battery.

With negative battery terminal temp removed... put a dc ammeter between neg battery terminal + neg post of battery.... it should read zero ma. If it shows current, you have something amiss, that is sucking the battery down by the next day. At that point, you can start removing fuses, one at a time, till the residual current drops to zero. Then you have narrowed the issue down to whatever that fuse(s) feeds.

Your AC Voltage of .027 vdc is 27 mv. Normal, ignore it.
You can read the battery voltage on the aeroforce gauge plugged into the obd port. Should read 14.3 to 14.4 vdc, with car on idle, and that's without the AC or anything else on.

Battery should read aprx 12.2 vdc every morning. If u see 10.9 vdc, either battery is toast, or something else is loading it slightly.

 

[redfirepearlgt]

^^^concur.

 

[s8v4o]

Battery should read aprx 12.2 vdc every morning. If u see 10.9 vdc, either battery is toast, or something else is loading it slightly.

12.2 is too low.

 

[LordBritish]

Ok, I checked the battery this morning and it was 10.4 VDC.

It was around 13 VDC yesterday after a drive.

So it lost almost 3 volts overnight just sitting in a parking lot.

Battery is toast !!

It says it was manufactured 10/13 and it says it's good for 6 years right??

 

[Dino Dino Bambino]

Consider anything over 3 years from a car battery a bonus.

 

[s8v4o]

If the diode is bad in the alternator it will drain the battery, possibly overnight. The alternator will be showing to charge like normal though. The diode just allows electricity to flow only one way. When it's bad the electricity can flow both ways which is why it drains the battery. Have you had the alternator checked? When you do they check for a bad diode.

I live in the heat of Louisiana and I average 5 years from my batteries.

 

[LordBritish]

If the diode is bad in the alternator it will drain the battery, possibly overnight. The alternator will be showing to charge like normal though. The diode just allows electricity to flow only one way. When it's bad the electricity can flow both ways which is why it drains the battery. Have you had the alternator checked? When you do they check for a bad diode.

I live in the heat of Louisiana and I average 5 years from my batteries.

I have not had the alternator checked but I did check the AC voltage of the battery when idling and it was 27 mv which is apparently normal.

 

[LordBritish]

I have not had the alternator checked but I did check the AC voltage of the battery when idling and it was 27 mv which is apparently normal.

I'll try to do a proper diode test later. Hopefully I can do it while the alternator is still in the car.

 

[LordBritish]

Ok, I did an alternator test by using the diode setting in my trusty Radio Shack digital multimeter.

First, I disconnected both cable ends (+ and -) from the battery.

Next I attached the red wire from the multimeter to the positive cable end (the part that was attached to the + post of the battery).

I then touched the black wire from the multimeter to the alternator casing.

Took a diode reading.

Then I switched the multimeter cables, black onto the positive cable end and red on the alternator casing.

Then, I took another diode reading.

I forgot which order gave which values but one reading gave 0 volts.

And the other one gave a reading that kept on climbing slowly, it was up to 1.1 volts and still climbing (slowly).

I'm guessing it's measuring the voltage of the batteries in the multimeter itself.

So based on this test, I'm assuming my alternator is OK unless my test is invalid somehow.

 

[redfirepearlgt]

Your multimeter is actually placing a voltage on the diode. A diode works like a one way check valve to keep it simple. Forward biased allows current flow, while reverse bias opposes current flow. The diode has two parts at simplest form. AN Anode (+) and a cathode (-). When a positive voltage is placed on the anode and a more negative is seen at the cathode the diode will allow current flow (aka forward bias). When the leads are swapped and the anode at a negative and the cathode is positive the diode blocks current flow (reverse bias).

hope that helps. And yes it sounds like the diodes are good. So go pick up a battery. LOL!

One last thing to remember. The alternators up to 2009 I believe had a mechanical clutch in them that would limit the RPM of the alternator as RPM's on the engine jumped up at sudden WOT to help minimize over spin of the unit. At what level the description of operation in the Ford technical manual did not say, however it is possible after all of these electrical checks you could still have an alternator that may have the built in clutch in the pulley going weak when spun above a certain RPM. Just keep that in the back of your head and don't let what you have learned and done feel like it has gone for naught should this bit of information prove out..........I doubt it but when troubleshooting IF the problem comes back that would be something to consider.

 

[LordBritish]

Thanks guys.

I measured the parasitic draw of the car and it measured 115 mA which seems like a lot.

Followed these instructions:
http://www.wikihow.com/Find-a-Parasitic-Battery-Drain

Perhaps it's the alarm system that's using that.

Is 115 mA too much ?

Anyhow, to be absolutely sure I repeated this test with the alternator cable detached from the battery. And again it measured 115 mA.

So I can conclude that my alternator is not causing the battery to drain.

This was actually educational

 

[Wes06]

When first reconnecting different systems power up so draw would be higher than normal till they stop running then drop to normal car off levels

 

[LordBritish]

When first reconnecting different systems power up so draw would be higher than normal till they stop running then drop to normal car off levels

Yea, initially it measured 1.0+ Amps but then settled down to 115 mA. It didn't get lower than that.

That might be normal for our Ponies with an alarm.

 

[Dino Dino Bambino]

I measured the parasitic draw of the car and it measured 115 mA which seems like a lot.

That's way too much so you definitely have a serious parasitic draw somewhere. The most likely suspects are either the alarm system or the Shaker ICE system (assuming you have one).

 

[LordBritish]

That's way too much so you definitely have a serious parasitic draw somewhere. The most likely suspects are either the alarm system or the Shaker ICE system (assuming you have one).

I just have a stock Shaker 500 (no Sub).

I may have higher than normal parasitic draw but 115 mA is unlikely to drain a battery from 13v to 10.4v overnight. May be over several days perhaps.

So my battery is still toast.

 

[redfirepearlgt]

Based on .115A current draw and using 13.1vdc as the avg voltage there is a device apparently that has a resistance of about 100-120 ohms causing the problem. That would be about the right coil resistance found on a relay coil if I recall correctly. No where near enough current draw to be an interior light or trunk light. Those items are likely 10-15 watt bulbs and would draw about .8 - 1.1 amps when left on. (P/E=A)

First I would do as many threads on this similar topic have suggested and pull the fuse that feeds your radio unit to see if that parasitic draw of .115 (115mA) goes away.

Then its time to just start pulling fuses until you can isolate the source of the current draw. It may even be a sticking relay like the PCM power control relay.

Hope to hear more.

Some have given up on this issue and simply bought a battery tender as .115A of current draw on a 40aH battery (avg aH rating for a car, Mustang may be higher. I can't remember) will drain the battery incapable of starting the car in about 10 days of sitting. Completely dead with only manual key entry (remote won't unlock the car) in about 14 days.

one last thought. Any chance you have a Kennebell boost a pump device or other device recently added (after market electrical) near the time that this problem became apparent? If so that's where I would start even before the radio at this point.