Battery or alternator???

[dennisafrompa]

2008 Bullitt would not crank outside a pizza shop last night. Got a jump from AAA and drove home (5 blocks)

It started this morning BUT the voltmeter does not move from the low position. The radio display says LOW BATTERY. Guessing alternator. What say you guys?

 

[09mb5854]

I am NOT a technician......

I would suspect battery. My reasoning - If it was alternator and it ate the battery to the point where it wouldn't start, when you jumped it and removed the cables it would have shut down.

I'd charge the battery and have a load test done on the battery..... Most big box auto stories will load test your battery in the parking lot for free......

 

[07 Boss]

Alternator.

 

[wabirch]

Original battery?

 

[Pentalab]

Put a digital voltmeter across the battery. Should be aprx 12.5 vdc with eng off.
With eng on, it should read 14.4 vdc. If it still reads 12.5 or less... the alternator is toast. You can also read the battery voltage off the OBD port. It's one of many parameters that can be displayed on the aeroforce gauges.

IF the battery was toast, it just won't hold a charge... but it won't suck the 135A alternator down to the point where the vdc is < 12.5 vdc.

If the alternator is toast, replace it with the 135A alternator from the 2010 mustang GT. The 2010 alternator drops right in....and is a 3 phase type. The 05-09 cars got the single phase version. Single phase alternator's went the way of the do-do bird years ago.

 

[Dino Dino Bambino]

Put a digital voltmeter across the battery. Should be aprx 12.5 vdc with eng off.
With eng on, it should read 14.4 vdc. If it still reads 12.5 or less... the alternator is toast. You can also read the battery voltage off the OBD port. It's one of many parameters that can be displayed on the aeroforce gauges.

IF the battery was toast, it just won't hold a charge... but it won't suck the 135A alternator down to the point where the vdc is < 12.5 vdc.

If the alternator is toast, replace it with the 135A alternator from the 2010 mustang GT. The 2010 alternator drops right in....and is a 3 phase type. The 05-09 cars got the single phase version. Single phase alternator's went the way of the do-do bird years ago.

Agree with all of the above but since the voltmeter still reads low with the engine running, it's almost certainly the alternator that's at fault.

 

[dennisafrompa]

So......

Yes, alternator is being replaced today.

 

[Dino Dino Bambino]

Looks like I've also fallen foul of the alternator gods. On my last couple of drives the voltmeter was reading below halfway even with no electrical loads and normally it would sit above halfway with the engine idling. Checked the voltage across the battery with my multimeter while the engine was running and it was just 11.1v. With the engine switched off it immediately rose to 11.7v.
I'll have to call the local stealership tomorrow and order a new 2010 alternator. In the meantime I'm not going to risk killing the battery (only a year old) by driving the car.