Battery? Alternator? Something Else?
 

So here is my issue:
1999 986 had been running well without issues, ~70K miles, 5 speed.
4/17 car wouldn’t crank (clicking noise only), had it jump started and I bought a brand new battery and replaced it on 4/18. Car ran fine without any problems until this morning 4/21 it again wouldn’t crank. I did some testing with a voltmeter and here are the numbers on the new battery (all numbers tested at the battery posts):

4/21 0700 - 10.8 Volts

After driving to work (25 miles) - 12.8 Volts with Car OFF

4/21 1700 8.8 Volts (again car wouldn’t start, in the interim it had been off, presumably no electrical load). Had it jump started.

After driving home (25 miles) without a problem - 13.9 Volts with Car ON

14.5 Volts with Car ON Full Electrical Load

Car OFF dropped to 13.8 Volts

One hour later 13.2 Volts, cranked it and started right away (dipped to 11.6 during crank) then came up to 14.5 with it running. Car off back down to 13.2.

I know this is a long post with a lot of numbers but I’m hoping you guys can help me sort out what the problem is. My thoughts are that the alternator is working appropriately given the above readings. I just can’t figure out why I’m losing charge. Any thoughts, ideas, experiences are much appreciated. Thank you.

Starter.
Sounds like the starter is dieing and wants more juice to turn over than even a new battery can supply.

Option 2 is that something is drawing juice when the car is shut down. Start pulling fuses and watch what your voltmeter does.

it seems like something is "on" draining the batt...if you put your volt meter between the cable and batt term i think you will see full batt voltage..start pulling fuses until it drops,easier said than done..let us know what you find

Thanks guys. I agree that I think something is staying on. Will start pulling fuses and see what I find. FYI battery was down to 6V this am with car off all night. can't imagine what would draw that much power?
@extanker: I'm confused... what do you mean by checking voltage at cable...which cable? and how would I see the full batt voltage? thanks.

take the cable off the batt ,hook up your meter between the two or put a test light between the two. there is gonna be some draw...eg keep alive memory,alarms,radio,clock

If your meter has a current setting, you can measure the Amps directly while connected in series with the disconnected cable.

Check both the front & rear trunk light switches, sometimes they stick and want shut off. :cheers:

Mini-update and more questions:
Not the front and rear trunk lights. Tested both of those with the voltmeter at the light socket, no voltage across either of those with the trunks closed.

I attempted to test all the fuses but was not successful. Maybe I am doing something wrong. I unhooked the negative battery cable and set my meter up between the negative terminal and free cable end. This gives me a voltage reading as expected of about 12.8V with the car off. However, nothing in my car works with this setup (i.e. even the lights don't turn on). What am I doing wrong? Is it my meter (it's a cheapie radioshack meter)?

Now with regards to the starter, can this be due to the starter? I don't see why the starter would be drawing any current with the car off.

Yeah, that's why I mentioned you have to use the current setting for that test. In Voltage test mode, the meter will not pass any current, that's why nothing works.
Does the meter have a current (DC Amps, not AC ) setting?

a [brief ?] history of checking for batt drain : hook up meter as you have or use a 12 volt test light and lets use an easy car 65 chevy...this car has no problems....there will be no readings from the test equiptment ....now if i open the door i will get a reading [door jamb switch] the lights wont work but the test equiptment is telling me ive found my draw.now lets say the does have a problem and to find it it will start to pull fuses BUT the door jamb switch is open and showing a draw so i find that fuse and pull it that way it wont give me a false reading...i keep pulling fuses until the light/meter goes out..maybe glove box light ...now we go to late model nightmares with 12 volt draw for 5 minutes until the car goes into sleep mode or the alarm system.there are specs for the mil amp draw but you have full batt draw [rag top ? check roof switchs] when the meter drops way down you found your draw just take the fuse for the open door out first....i believe your starter and alt are ok...check ignition switch power outlets ,light switch, make sure key is out of switch...good luck

That method will work with a TEST LIGHT, because it will pass current ( enough to light the bulb ) , but it won't work with a VOLT METER, because it will not pass current.

he is getting readings on his meter...i dont know what kind of meter or at what setting just that hes reporting voltage...i think there are so many systems on these cars that neither way will find it

The numbers you post are OK - except for the low battery onl;y numbers - how old is the battery? If 5 yrs. or more replace. If 3 yrs. or more, seriously consider replacement.

Battery has 6 cells each producing about 2.2 VDC - wired in series total = 12.0 - 13.2 VDC.

Bosch alternator produces 13.5-14.5 VDC.

Suspect battery, bad starter, or starter relay. Cannot rule out bad ignition switch also.

I don't believe anything is drawing power with the car off, other than those things which normally do. I believe your battery is old, sulphated, or has a bad cell which does not allow it to hold a charge. Age means nothing. You can buy and install a new battery, take the car out, hit a good pothole and damage a cell, it can happen at any time. Rare, but it does happen.

Cheers!

LB - in his first paragraph, skadakia says he has fitted a new battery..... and as you correctly say, problems do occur with new batteries, though I wonder how "charged" his battery is??

skadakia, what stephen wilson & extanker are talking about is the draw on the battery with the engine off and the key removed - we call it "dark current" and its in miliamps (mA).
If you remove the + cable from the battery and connect your meter between the battery terminal and the cable end (in series) and switch your meter to DC Amps, you will get a reading - usually about 10-20mA. This current is feeding the clock & alarm system etc.
If you see a reading of say 100mA, you have a current draw which is over and above the norm and the way to isolate this draw is to leave the meter connected and start removing each fuse. When you see the current draw change (drop) when a particular fuse is removed, you have isolated the faulty circuit.

One other thing, you cannot fully charge your battery with a 25 mile drive. You really need to trickle charge it for at least 12 hours for a decent charge.....

Updates
 

OK guys, thanks for all the tips. I spent the better part of this weekend troubleshooting.
I think all signs point to the alternator being the culprit.

Battery is brand new as stated. I took the battery down to AutoZone, they tested it and said it was OK and recharged it for me.

Got an Ammeter set up to show me the draw and I found out that my draw was +3 Amps (not 3 hundreths or 3 tents, 3 full amps) with the car off (no key even in the ignition).

I pulled every single fuse to no avail. Only 1 fuse gave me some hint of a response. There is a 25 Amp fuse labeled "Engine Electronics" (Block C, Row 1). When I pull it, nothing happens however when I reinstall it the amps temporarily dip down (to like 500 mA) then immediately right back up to about 3 Amps.

I then removed the +12V hookups from the Starter and still had a 3 Amp draw.

Finally I removed the Alternator and my draw fell down to 10-20 mA.

Now the only glitch in all of this is that I took the Alternator to AutoZone and on their test it "passed" all 3 categories (regulator, rectifier, and something else). I can't explain this. My thought is that either their test is not looking at how much current the alternator draws but only that it's output is correct. Or that with the alternator connected, it completes a circuit to something else that is shorted.

I have ordered a new Alternator and will receive and install it tomorrow. I'll update everyone with what I find. Thanks again for the help.

Update #2
 

It has to be the alternator.
I connected the alternator to a charged battery with jumper cables and placed my ammeter in this circuit. The current is 3 amps. This is external to the vehicle without any other circuits involved and without the alternator connected to anything else.
I get the remanufactured Bosch alternator tomorrow from local auto parts store. Will install and give the final updates. Thanks again.

Why can't you just go to an autozone or advanced auto and have them check it on their machines? They are able to determine if you have a good battery, alternator, etc...

FYI make sure they enter in the correct cranking amps for your battery when they test it.

I took my alt to oreily's (sp) autoparts store($214) and they couldn't even get it to read. I had them check the new/reman before I took it home as it is more of a pain to install the new one. New Battery and new alt solved all my problems. Hopefully you should be good to go. check the "DIY" section on here and Pedro's garage for help, if you need it.

I don't know where you are talking about, but advanced auto and autozone check your battery and alternator for free. Walmart will check your battery for free too, but I don't know about the alternator. Just tip them a couple bucks.

OK, new (reman) alternator installed tonight. Everything seems to be working OK so far and the Volts are measuring appropriately. I can't check the amp draw because I did something stupid and blew the fuse on the ammeter. So I'll have to wait till I can buy a new fuse for it, or I'll know if everything is OK if the battery is still holding Volts over the next day or two.

Thank you very much to everybody on this board for all your help. Now off to drive until the computer re-learns everything like the RPMs.....(anyone know how long it takes for the computer to readjust to everything by the way?)

Thanks....