Alternator, Regulator, Or Battery?
04-05-2009, 03:33 AM
#16
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our batteries, for some reason, are the ****tiest part of our cars. My FS Bronco's battery lasts and works everytime for YEARS ... I let it sit there for months undriven and it cranks right up. The Porsche ... leave it for maybe 2 weeks and the battery needs replacing.
04-05-2009, 09:57 AM
#17
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its not the battery thats bad its the sub systems that have a continuous draw.
Plus some of the relays that are now 20 years old will either stick or just have dirty contacts, that keep drawing power
Plus some of the relays that are now 20 years old will either stick or just have dirty contacts, that keep drawing power
04-05-2009, 06:11 PM
#19
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Alan - Ok small terminal was connected, with the small wire disconnected I tested the voltage on that wire only and didn't get any voltage. On the large terminal connection from the battery, there was 12.4 volts. I grounded the small wire out and the charging light came on. So what does this all mean? Is this the exciter circuit or is it the alternator? From your post below, I am thinking it is the exciter circuit. So what now?
Since on a 928 they are integrated together it makes no difference. On some cars they are separate.
In this case it is for sure the alternator that is at fault from your description - keep the battery charged and do not get a replacement unless you have a very good warranty deal... you don't need it. .
First does your charge light come on in ignition bulb test mode? if no I'd debug that.
Check the small terminal on the alternator - is it connected? if not - connect it (check the wiring from when it was laying on the ground - did something pull loose?
If it is connected disconnect it and see if with the ignition on you get 12v on it? If yes - ground it to the chassis & see if the charge light in the dash comes on? If either of these fails you have an exciter circuit to deal with. If both are OK take the alternator out and take it to a good repair shop for testing, if it is the regulator/brushes they can replace that easily & relatively cheaply.
Alan
In this case it is for sure the alternator that is at fault from your description - keep the battery charged and do not get a replacement unless you have a very good warranty deal... you don't need it. .
First does your charge light come on in ignition bulb test mode? if no I'd debug that.
Check the small terminal on the alternator - is it connected? if not - connect it (check the wiring from when it was laying on the ground - did something pull loose?
If it is connected disconnect it and see if with the ignition on you get 12v on it? If yes - ground it to the chassis & see if the charge light in the dash comes on? If either of these fails you have an exciter circuit to deal with. If both are OK take the alternator out and take it to a good repair shop for testing, if it is the regulator/brushes they can replace that easily & relatively cheaply.
Alan
04-05-2009, 06:16 PM
#20
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Actually those results don't make any sense... can you retest.. if your charge light came on with the small connector grounded - it pretty much has to have some voltage on it when its not connected.
Assume you know how to use a voltmeter...? ground to the alternator case in this instance... You should have 12v on that disconnected wire with the ignition on...
It actually sounds like your exceiter circuit probably works OK... which tends to still point to the alternator.
Don't take it to a general automotive place for testing (they are fine for batteries but not this). Take it to an alternator/starter rebuild place - they will know what they are doing
Alan
Assume you know how to use a voltmeter...? ground to the alternator case in this instance... You should have 12v on that disconnected wire with the ignition on...
It actually sounds like your exceiter circuit probably works OK... which tends to still point to the alternator.
Don't take it to a general automotive place for testing (they are fine for batteries but not this). Take it to an alternator/starter rebuild place - they will know what they are doing
Alan
04-05-2009, 09:28 PM
#21
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It had minor voltage such as .24V or something of that sort. I double and triple checked, grounded it out and the voltage warning light came on. I will double check after I yank the alternator off, again. This is with the ignition on, not the car started right?
Where does that small wire come from? The starter? Maybe I can trace it back and check voltage at another point?
There is a local rebuilder that I will take the alternator too to have them check it and rebuild it if necessary.
Where does that small wire come from? The starter? Maybe I can trace it back and check voltage at another point?
There is a local rebuilder that I will take the alternator too to have them check it and rebuild it if necessary.
04-05-2009, 09:41 PM
#22
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Yes the test is with ignition on car not started and the small wire not connected - you should in this case have battery voltage on that wire. The fact that the charge light comes on when you ground this wire under these conditions suggests it is connected fine.
It is fed from the ignition switch via the charge lamp - it loops through the CE panel but there are no other functional connections...
When actually connected to the alternator under these conditions it should be a low voltage - probably less than 1v - until the car is started & running - then it should go to ~ system voltage (whatever the alternator puts out).
Alan
It is fed from the ignition switch via the charge lamp - it loops through the CE panel but there are no other functional connections...
When actually connected to the alternator under these conditions it should be a low voltage - probably less than 1v - until the car is started & running - then it should go to ~ system voltage (whatever the alternator puts out).
Alan
04-05-2009, 10:09 PM
#23
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Alan, I tested it again and it did show around 12V this time so it definitely is not the exceiter. I got the alternator off and it will be off to Vance electric to get tested. I have no idea what happened earlier today other than the voodoo curse that is over my head today.
04-06-2009, 09:52 AM
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The alternator I pulled off the car is a bosch unit, is it the 115A model? How do I determine the model/amperage. I believe it is since I think the Paris Rone units are the 90A units.
04-06-2009, 10:21 AM
#25
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My battery in the 928 is now ten years old. I've never run a trickle charger on it or done anything other than leave it alone. It does have a window where I can see a little pink bunny with a drum.
04-06-2009, 10:28 AM
#26
Team Owner
just for kicks check the hot post connections under the 11mm bolt and the 14 connector , if you dont have a cover then a 1988 S4 cover will fit
04-06-2009, 02:19 PM
#28
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Rick - whatever you do - don't bring that battery to Phoenix... it will spoil its batting averages in no time...
When I lived in England the relatively mild climate seemed to be much less threatening to batteries - they lasted for many years there too...
Alan
When I lived in England the relatively mild climate seemed to be much less threatening to batteries - they lasted for many years there too...
Alan
04-06-2009, 03:57 PM
#29
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The alternator main terminal is connected by a very big wire to the starter and the battery... it really cannot be at .24v unless the battery is dead...
The jump post at the front is also connected to the battery & alternator by a big wire... measure there. When running - the system voltage there should be ~ 13.5-14v
When not running you will have battery voltage ~ 12.7v.
The alternator main terminal should never be more than a few mV different than the jump post reading...
Are you sure you have the correct connection on the main alternator post?
Alan
The jump post at the front is also connected to the battery & alternator by a big wire... measure there. When running - the system voltage there should be ~ 13.5-14v
When not running you will have battery voltage ~ 12.7v.
The alternator main terminal should never be more than a few mV different than the jump post reading...
Are you sure you have the correct connection on the main alternator post?
Alan
04-06-2009, 04:01 PM
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Alan, I tested the small wire again last night (see post #23) and I got about 12.4 volts whatever the battery was reading. So it definitely is not the exciter circuit and it is the alternator. I am taking my alternator to a decent shop to have it tested tonight and possibly rebuilt.
Matt
Matt