Alternator?

[loccusst]

Went out to my car this morning and it didn't want to start. New battery 12/11. Alternator tested 14.5v at the alternator. Battery tested 11V at the terminals and when testing with a DMM at positive terminal on battery and grounding point on chassis. Thinking that there could be an issue with the alternator but want to know your guys thoughts before I rip it out to get tested since is freezing cold here. I was messing with the Vag com last night to reset the service message and the car started rough while in the garage before I was messing with the vag, but started fine when I was done.

 

[A41.8QTM]

Sounds like the alternator is fine but your battery is on the way out if it's only giving 11v.

 

[eurocars]

Did you test the battery with the ca running to see if its getting the same voltage as the alternator? If its 11v while its running, try doing a voltage drop test on the alt cable

 

[loccusst]

Yeah the 11V was while the car was running, so it's not getting the same as the alternator. How do you do a voltage drop test?

 

[eurocars]

one lead on the big cable that bolts to the back of the alternator, the other lead to the end of the cable where it bolts to the fuse box bus bar. should read less than .5v

 

[loccusst]

I drove the car to work 2 hours ago, went out to start it just now and it wont.

 

[loccusst]

one lead on the big cable that bolts to the back of the alternator, the other lead to the end of the cable where it bolts to the fuse box bus bar. should read less than .5v

Are you saying it should show less than a .5 volt drop between the two? My wife is bringing me my DMM to work at lunch so I can figure it out.

 

[A41.8QTM]

If the car is running you aren't testing the battery, you're testing the alt. Your battery should be getting very close to whatever the alt is putting out. You already confirmed that it is only getting 11v with the car running so you are dropping 3.5v.

 

[loccusst]

So started the car, let it run for a bit and then tested while car is running. there was a .8v drop from the alternator to the fuse box bar. The same drop was there from the alternator to the battery terminal. The battery still isn't anywhere near the voltage the alternator is putting out. I checked for voltage drop on the negative terminal to the alternator mount and it was very minimal. I checked both battery terminal connections and they are clean and tight. After running for a while the battery was holding at 12.5v with the car off. It's running right now and then I will go test everything again.

 

[loccusst]

Tested the car again. 13.5v at the alternator and 11.4v at the battery. turned the car off and tried to instantly start it. No go. Not enough to restart. IS the battery bad? Is the alternator not charging the system?

 

[eurocars]

how old is the battery?

 

[loccusst]

Replaced before last winter...11/2012.

 

[loccusst]

Talked to a buddy of mine who is a tech and he thinks it could be the cable from the alternator to the bus bar that is actually bad. So I will see if I can find a replacement locally at an auto parts after work. Why does it have to be so damn cold outside?

 

[eurocars]

if that ends up being it, you will have to pull the intake manifold to replace it

 

[A41.8QTM]

11/2012 is only 3 months ago - it should be under warranty.

Replaced before last winter...11/2012.