[968TDG]

Hey guys, 

 

So I've been out of the country for 11 months, and just got my 968 started again.  Everything is working well, except the alternator is not charging the battery at all.  I noticed it last night when I was taking a short drive.  The voltmeter was reading 12 volts, and started to go down from there over the course of a few minutes.  The lights started to dim, and by the time I was back home, I had less than 11 volts at the battery.  I verified this with a voltmeter, with the engine running and off.  So far I've inspected the cables at the alternator and traced them to the starter, and don't see any damage or bite marks from rats.  I will say that the larger cable at the alternator has the wire exposed, but it doesn't look damaged.

 

Any thoughts on what might be the cause, or how to trouble shoot?  I read on Pelican that if I disconnect the three wires from the alternator (I only see two) and test to ground with a voltmeter, I should see the battery voltage, so that's what I was planning to try next.  I don't think the alternator has ever been replaced so I suppose the brushes could have worn out, but the fact that it is not working at all, at any rpm, and isn't intermittent, makes me think it is something else.  Maybe the voltage regulator?

 

Cheers

Phil

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[ds968]

Voltage  regulators are a separate unit attached to the main body of the alternator ( unlike many other cars where they’re integrated in the alternator and you have to replace the entire unit ) so they can be replaced separately if they go bad , which is good news because they’re inexpensive and a fairly easy job. 

The usual test is to fully charge the battery , attach a voltmeter to it and start the car ; if the voltage jumps from 12.4-12.8 ( battery with the engine off )  to 13.4 -14.2 right away, while the engine is running,  the alternator is charging ok,  although if you experienced the lights dimming while driving and the battery drained by THAT MUCH by the time you got home, it could be the alternator or voltage regulator going bad or dead , but never discount the possibility of a dying battery either.  If they’re bad, won’t hold a charge, no matter how well the alternator works.  Have the battery tested under load , that’s the cheapest process of elimination m.o. , before spending tons of money on a new alternator . 

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[MCL968]

I agree with Dan, check the battery first, since they really don't like sitting for that long, then go to the regulator.

 

A hassle to change, but easier than the alternator.

 

https://www.ebay.com/itm/For-Porsche-911...Sw1uRZr6tH

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[Kaj Hallstrom]

I just went though this whole scenario. Tested everything and found the battery guilty as charged. It was 8 years old so it was a clear suspect.

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[ds968]

 I said replacing the regulator was “fairly easy” because I did not do the job myself  :closedeyes:  but watched my mechanic do that ..accessing the spot and with limited room around it to work is a bit of a PITA ; he had the car up on the hoist, had all the right tools, not to mention lots of professional experience, so it was not too difficult for him and didn’t take much time.   

But definitely start with the battery ..one bad cell, and that’s all it takes to manifest in that manner .  

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[snova]

funny, I was just going to ask about the alternator.  I can charge the battery just fine with a trickle charger, so I'm relatively sure the battery is fine. Its only a year old.

 

The alternator starts charging fine.. around 14.3 volts.. but as the engine bay gets hotter it keeps lower the voltage that its pumping out.  Eventually barely over 12 volts.     Eventually the battery drains because its running the cooling fans, lights, etc and the alternator isn't keeping up.   If I let the car cool down, and start again the alternator again starts charging full blast at 14.3 volts.

 

Besides the voltage regulator, could it be something else which is temperature dependent?   The fan on the front of the alternator is designed to rotate counter clockwise if you are looking from the front of the car at the alternator fan.  I put my hand  while the engine is on and its push a lot of hot air.

 

anyone experience this?  voltage regulator or cooling issue?  the housing is hot to the touch.  I can use an IR temp gun if that's helpful to get a reading of how hot the alternator housing is getting.

 

p.s.  as I understand it the voltage regulator is supposed to shut down if things are getting too hot.  so, wondering if something else is wrong to cause the voltage regulator to shutdown.

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[Roboman]

TDG ..... +1 on all those who suggest the battery.  Just grab a battery from another car and run your engine, no need to go anywhere, just watch the voltmeter .... you know it should surge up to around 14v when you are revving and settle around 12.5v at idle. Turn your lights on, see if the voltage holds. Your meter is not always accurate, but provided there's a couple of volts difference between rev/ not-rev then your alternator is okay. 

 

Someone else can confirm, but I was told NEVER run an alternator off load else you will toast it.

 

You didn't say if you disconnected your battery before leaving the car for 11 months.  If you are going away for some time the best thing to do is remove one of the battery connections, and when you return all should be fine.  I did this for 7 years with a car parked under our house for about 8 months at a time; every time I returned I just reconnected the battery and away we went.  If you don't disconnect the battery the clock, alarm system, and other "background functions" will gradually erode the charge and kill the cells.  Good luck!

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[968TDG]

Thanks for all the responses.  I did unplug the battery before I left (AGM red top), as even a month or two of leaving it attached will drain it in my experience.  I charged the battery before trying to start the car, the AGM charger said it was at 55% when I started charging, and took about an hour to reach full charge.  After driving the car, and noticing the volt meter, and double checking that it was correct at the battery with a handheld voltmeter, I attached the charger again, and it said the battery was at 13%.  The battery certainly may need replacing, but it was a month old when I left.  As for the accuracy of the volt gauge on the cluster, I had the common issue of it being pegged at 16 volts, and sent the cluster off last year to be fixed somewhere in Hollywood.  It does appear to be accurate since the repair, but as I mentioned, I always double check it at the battery because I don't trust the gauges.

 

So here's a question.  with the car running, the voltage doesn't go up, and that's why I assumed it's the alternator, voltage regulator, or wiring.  Is it possible for a bad battery to give this same symptom of no increase in voltage?  I'd always assumed that, even with a toast battery, with the car running, you'd still see an increase in voltage...

 

I have a warranty on the battery, so I'll probably just go to the store and swap it out today to eliminate that possibility, and see what happens with the voltage.

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[94SilverCab]

What about the belt? 

 

Jay

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[968TDG]

I have the supercharger installed, and the belt seems to have plenty of tension.

 

   

 

 

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[ds968]

Oh man, let’s hope it’s not the alternator itself ..I have been informed by my mechanics ( both my ex-mechanic now retired, and my current one ) that with the SC there, replacing the alternator will be a major PITA job, which involves a considerable amount of SC disassembly .  Oddly enough, Flash told me the same thing. 

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[968TDG]

Yeah...it's tight in there.  I just got under the car and measured the voltage at the main post on the alternator with the car running, and it was just the battery voltage (12.06 V), so it seems like the alternator isn't putting any power out...maybe it's the voltage regulator.  I'm not sure if I'll be able to replace it in situ, but there is some clearance from the bottom.  I assume if the alternator is spinning, and it's not creating power, it's the voltage regulator or brushes, and it looks like the replacement voltage regulator has the brushes attached to it, so it seems like the culprit, unless anyone else has insight on what else could cause this symptom...

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[MCL968]

Sounds exactly like the problem. BTW, there are adjustable regulators out there for a few more bucks, you may want to go with one of those. There is a small hole in the back so you can use a jewelers screwdriver to adjust the voltage.

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[Roboman]

After one year your battery should be fine, but of course it may not, and a dead/damaged cell will result in poor charge retention.

However, the cables between the alternator and battery and earth strap may have rotted on the inside which would also impede charging.

Then there's the alternator assembly.

And Jay is right, check the belt ..... don't worry about tension, just make sure the alternator is spinning.


The voltage at the alternator will be the same as across the battery, there should be minimal volt drop across the cable itself. So if you're getting battery voltage at the alternator base it suggests the cables are okay. But it does no harm to check these things... Do you have access to booster cables?


Using your hand held voltmeter.....

If you have jump/booster cables you can sit a known good battery on the floor, hook it up (disconnect one of the terminals on your battery) and run the engine and check at the battery on the floor with your voltmeter ....

If that doesn't help then you can check your alternator cables by clipping the booster cables onto the back of the alternator.... go carefully in there as there's a lot of opportunity to touch/short to earth....again use your voltmeter to check charging ..... (It is possible your engine won't turn over at this point as you are trying to supply power up through your alternator cable. So if it has rotted then there may be insufficient current passing through the cable)

Once you've eliminated the battery and cables from the equation then you're left with the alternator assembly. Personally I would just change the regulator as that's the cheapest and easiest next step. But it's not based on trouble shooting so you may still be up for another alternator.

I hope this helps... apologies for my step by step approach, I'm an ex-professor of engineering; can't help myself

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[pdxmike]

As an FYI: 

 

 

 

I will say that the larger cable at the alternator has the wire exposed, but it doesn't look damaged.

 

This is the warning sign that your alternator to starter harness insulation has failed and needs to be replaced ASAP. Part number is 944 607 029 01. Until replaced, park it in neutral with the ebrake on.

 

http://www.968forums.com/topic/16302-fai...nsulation/

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[MCL968]

As an FYI: 

 

 

This is the warning sign that your alternator to starter harness insulation has failed and needs to be replaced ASAP. Part number is 944 607 029 01. Until replaced, park it in neutral with the ebrake on.

 

http://www.968forums.com/topic/16302-fai...nsulation/

WHOA, that is a major red flag. Mike is right, get it fixed before the car drives off without you.

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[968TDG]

Wow, that's awful!  What a dangerous design!  I've just unplugged the battery, and made sure it's it neutral with the handbrake on.  I read through the Pams968 thread, and I have all the same symptoms: 

 

-multiple knock sensor check engine lights

-check engine light at idle sometimes that goes away when I rev the engine.  

-battery drains quickly, and I've had to replace multiple times in the past several years

-exposed wire at the alternator

 

I ordered a voltage regulator, which just arrived, and I'm ordering the cable now, and wont plug the battery back in until I've replaced it.

 

I'm extremely grateful for everyone's input, this could have been really bad...I live on the edge of a 100 foot bluff lol! 

 

As always, what a great community!

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[snova]

funny, I was just going to ask about the alternator.  I can charge the battery just fine with a trickle charger, so I'm relatively sure the battery is fine. Its only a year old.

 

....

Famous last words of me to live in infamy.  Off I go to the hall of shame.

It was the battery!!  After I need a jump start last night, I took it over to Napa to get it checked.  They said, its fine..  fully voltage good cold cranking amps.   so can't help you.   I'm like WTF?  how can it be fully voltage I just needed to get a jump start 30 min ago, it couldn't have charged by now. So I took it over to O'Reilly.   Its bad sir, yes.. voltage is 12.5V but its fails our tests on our machine.   We have a different type of device in the back... be right back.... yes, it fails on this one too.  So I head over to a different Napa,   they test it on their machine.. Same things.. it look good.   Then some smart woman in the back says... here put a load on it with this and test it again.   Bam.   Fail!       1 year old Napa Premium AGM Wet battery.   Stick in the replacement battery... holy cow!   14V after 2 hours of driving with high beams, heater and fan on full blast.  Lighting up the street like no one's business.. wow these headlights are so bright. Had no idea.

 

all this time.. so many problems as I think about it now..  1 voltage regulator, and 2 alternators got killed because of this POS.

I made my mind up to buy a good battery tester and test all my batteries myself from now on.  So many hours and dollars wasted :-(

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[ds968]

Great news !   :clap: 

 

( even brand new batteries can come out of the box with a bad cell and they fail prematurely .  it’s rare, but it happens )

 

I’ve had nothing but Interstate batteries in all my cars , for as far back as I can remember , and have never had a single problem with them ..they typically last about six to seven years ..


 

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[snova]

Great news !   :clap: 

 

( even brand new batteries can come out of the box with a bad cell and they fail prematurely .  it’s rare, but it happens )

 

I’ve had nothing but Interstate batteries in all my cars , for as far back as I can remember , and have never had a single problem with them ..they typically last about six to seven years ..

For some reason I can’t find anyone who sells them locally. Did research and it looks like best rated are odessey and acdelco.

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