Need help on how to diagnose a charging issue: 83 SC

[mhackney]

This is going to be a long story - sorry in advance!
My car: an '83 911 SC Cabriolet

Last weekend a friend (I met here on Pelican a long time ago!) helped me drop the engine/tranny to fix a leaky input shaft seal. That all went fine. Afterwards, I drove home and installed a Kenwood KAC-M1824BT 45watt/channel amplifier that lets me stream music from my iPhone via bluetooth. Once I had that installed I went out for a 50 mile test drive in prep for my monthly trip from MA to Rochester, NY. Everything was fine, this was this past Sunday. On Monday I drove about 60 miles on a couple of errands. On Tuesday (yesterday) I left for the 280 mile trip to Rochester at 5AM. I listened to the new amp for a few hours on the trip (a 6 hour trip). That went fine. In Rochester I drove another 50 miles. Again, everything was fine. This morning I drove to my office from the hotel, again fine. Now the fun begins...

At noon today I left Rochester heading east on the NY Throughway. I had the top down, headlights on, amp cranked up almost all the way so I could hear over the wind noise and I had my iPhone plugged into the cigarette lighter charger because it was consuming a lot of power with Waze and streaming music from Apple's new music service (in other words, it was sucking a lot of power to do all this!).

I made it about 150 miles when I noticed my tach needle jumping up to 6K. Then it went back to 3.1K and all was good. 15 minutes later it happened again. This continued and worsened until about 45 minutes later the tach dropped to 0 and stayed and then I noticed my amp was cutting out and the car starting to loose power. Prior to this I was going through debugging in my head and came to the conclusion that I was draining my battery with all of the power consumption (lights, amp, iPhone). So I turned off the amp, pulled out the charger for the iPhone, turned off the lights and within a minute the tach came back to life and the car was running fine again. I was getting close to Albany and I like to take back roads from Albany home through VT and NH and felt safer in case I died along the way - I don't like having to pull onto the shoulder on highways!

Once I got off the highway heading through beautiful Troy, NY (I can say that, I lived there for a few years!) I was sitting at a light at the bottom of a long steep hill (everything is uphill from Troy) and when I started the tach needle dropped to 0 again and the engine had power problems. This was about 30 minutes after I had turned all the electronics off and had not had a problem. I nursed it up the hill and at the top the tach sprung to life and the power picked up. I drove conservatively on the backroads - 55 MPH - and didn't have a problem for over 90 minutes. I thought maybe I was right and the battery was now starting to charge up. Then I had to stop for gas at a small town in NH and when I tried to start the car, it wouldn't turn over.

I spotted a woman talking to someone sitting in a truck and walked over to ask the driver if "he" had jumper cables. Turned out to be a woman and she said "no, I don't". But the woman standing chimed in "I have some!". The woman in the truck then said - "she's single and looking for a rich guy!" and winked as she glanced at my cabriolet. But I digress...

The woman with the cables was quite nice. I hooked up the cables and we chatted for a few minutes while I charged the battery a bit. The car started right up. I thanked her profusely and drove off.

I was about an hour from home and it was getting to be about 6 PM and darkening. I left the lights off. The tach started jumping around again and continued to do this and drop to 0 every 10 minutes or so but I was able to continue driving. About 5 miles from home, the tach dropped to 0 and the battery charge light lit up brightly. I had noticed that it flickered dimly a few times but now it was bright. I made it home and here I am!

Now I need to diagnose the issue. I've owned the car for 8 years. The battery was in the car when I got it so no telling how old it is. Same with the alternator. I've had cars loose an alternator and battery die in the past (non Porsche) but the symptoms were a bit different than this so I am a but stumped. My friend and Pelican confirm that the jumping tach needle is an early charging system symptom. I'm assuming that the extra power draw from the amplifier slowly drained the battery. Once I turned it off, I would think the battery would charge and all would be ok as long as I didn't use the amp or lights. But that was not the case, I continued to be right at the edge of having enough power to run but no more.

How should I go about diagnosing this? I am going to be out for the next 2 days but when I get back on Saturday I want to dig in and fix this problem. I would assume that a properly working charging system should be able to handle a 45Watt amp and lights!

cheers and thanks for hanging in there,
Michael

PS I'm married but if anyone wants to meet a nice woman in south west NH, I have her number!

[wwest]

First, NEW battery..

Second, you dropped the engine..

All connections restored and tightened, most especially the starter solenoid/alternator connection?

[mhackney]

Thanks west. I am charging the battery now since I can't do anything until Saturday. It was near dead when I put the charger on.

Yes, we were systematic reconnecting everything and my friend has dropped many 911 engines. I have a lift so I will triple check the connections on Saturday as a first step.

[boyt911sc]

After charging the battery, install a voltmeter that you could plug to the cigarette lighter receptacle so you could monitor the voltage during your drive. The problem could be your battery or your alternator. If your battery is more than 6 years old, time for a fresh one.

Tony

[mhackney]

Thanks Tony, I don't have an adapter for my voltmeter to plug into the cig lighter reptile but I can rig one up or borrow one. That battery is at least 7 years old (the time I've owned the car) and likely older.

[87maniac]

This is what I have. $12 at amazon.
Good for monitoring alt. output and battery charge,
can see if alternator is over/under voltage while driving.
Plus it has two usb ports for charging phone.

Your alt is not charging the battery, or your battery is toast.

[Jdub]

The ground wire from the alternator to the engine must be solid, and then the ground from the transmission to the body must also be solid. Be sure your battery ground and terminals are also clean and well connected.

I never, ever take a chance with a battery as they hide bad cells, etc. over time if they've been smoked (smell any rotten egg in the cabin?). I would think hard also on the alternator - what is the history on this - how old, rebuilt?

Point is, once you start frying the battery and alternator you can do some damage to the system. Also, just so you are aware, I believe the car will cut out totally if the tach needle exceeds a point within redline - the car shuts down. Not something to f*{k with at all!

[Dr J]

I would take out the battery and have it tested. You can get it done for free and immediately rule it out or in. I haven't had batteries last 8 years for me. The other thing you can do if you have a voltmeter is get a voltage reading after charging it. Fully charged you should get 12.6 v or therabouts. With the car running it should be higher than 13 V.

[mhackney]

Thanks folks. I've owned the car 7 years and have not had to touch the battery or alt. I charged the battery overnight and checked it at 6am as I was leaving. Read 12.6 volts. I will check all the grounds when I return on sat. I also ordered one of those charging system testers and it will arrive on Saturday too - thanks for that idea.

No smell of eggs at all. I know that smell from another vehicle a few years ago. I know w how to proceed on Saturday so thanks. Einstein said the simplest answer is usually the correct answer. My hypothesis is a dead battery. If the alt were unable to generate current I don't think it would have made it home 3 hrs after I started seeing issues. I'll report back though for closure.

[mhackney]

Ok, an update...
Now that I'm back home I started diagnosing the issue this morning.

Firstly, the battery is an 85 month Interstate Mega-tron plus 850CCA. I was apparently installed in May of 2004! (only the "4" is pushed in the row of numbers).

Now for some diagnostics. Firstly, UPS delayed deliver of the cigarette lighter tester so I don't have that yet but I do have a multi meter.

I measured the battery after sitting for 2 days at 12.23V - a bit down from the 12.6V I read after charging on Thursday. I then started the car. It cranked over but not as crisply as usually. I hooked up the DMM so I could see it from the driver seat. It reads 12.23V with the engine running but no accessories on and at 1000RPM. Accelerating to 3000RPM has no effect, the voltage is between 12.22 and 12.23. Turning on the headlights drops the voltage down to 12.18V. Turning on the new amplifier had no noticeable voltage drop (maybe .01V).

So, it seems that the alternator is probably the culprit although with an 11 year old battery that may not be conclusive? In any event, I think I'll replace the battery, I think I got my money's worth out of this one! But I don't want to risk screwing the new battery if there is a voltage regulator issue. This is an 83 cab with the internal VR to the alternator. I've read the charging system info in Bentley 911SC manual. Of course everything starts with a good battery so off the gate I am unsure about that until I replace it. But on 270-13 it mentions that when accessories are turned on, if the voltage stays the same it is likely the VR, if it drops, it is likely the alternator. In my case it drops. But, this section also says to make sure the belt is tight so I have to adjust that as a prerequisite too.

My alternator belt is also on the loose side so I need to correct that. I have a new belt so I'll go ahead and install that since I don't know the history of the existing belt.

Any other suggestions?

[wwest]

You should think of the (full of electrolyte) battery as a HUGE power zener diode, as long as the electrolyte hasn't boiled off it will tend to "lock" the post/terminal voltage at no more than ~12.6 volts.

The proper place to check for alternator output voltage, short term voltage spikes, is as near the alternator electrically that you can to measure, the fuse panel in the engine compartment.

Take a DC measurement, and a capacitor coupled AC measurement. The battery is especially good at "sinking" short term voltage spikes.

[wwest]

Bottom line... battery good, alternator/VR.. BAD.

But I would suggest replacing the battery anyway.

Sounds as if your entire experience was the result of intermittent functioning of the alternator/VR.

[mhackney]

Yes, I plan to replace the battery but no one in the Boston area has one in stock that fits and Interstate (my preferred) is not open on weekends so I won't know if they have it until Monday. Firestone carries Interstate but they don't have it either.

Meanwhile I replace and adjusted my belt properly. The old one was pretty beat and loose so that was good. I need to measure the alternator output now. I don't know which terminals in the fuse panel is from the alternator so I'll have to track that down.

[mhackney]

Meanwhile, any recommendations on an alternator? Given they have a $115 core charge it would be ideal to find a local source since I can bring the old one in.

[Bob Kontak]

Originally Posted by mhackney

I need to measure the alternator output now. I don't know which terminals in the fuse panel is from the alternator so I'll have to track that down.

Just measure it at the battery.

[mhackney]

Thanks, as per wwest's post it is best to measure as near the alternator as possible so that is what I am trying to do. It looks like the alternator output goes to both terminals 23 and 24 in the rear fuse box. Those are easy enough to find.

EDIT: I took a DC measurement as that's all I can do. Still at 12.23-12.25V. I need this car to be reliable during the driving season so it makes sense to just replace the alt and battery given that I don't know the history of either component (well, the battery I now know is 11 years old!).

[mhackney]

Other than the alternator (and I have a new belt just installed today) is there anything else parts wise I need? I can't afford waiting for multiple serial shipments! There is something on the Pelican part that says that a clamping cap 911-603-428-01-M100 may be needed. It would seem that the existing part on my alt would work?

Looks like a new (not rebuilt) Valeo is the way to go.

[Bob Kontak]

Originally Posted by mhackney

Looks like a new (not rebuilt) Valeo is the way to go.

I like this option. You can get a rebuilt Valeo for half, like I did, and it may be just fine, like mine has been. Except, from what I can hear, the bearings have never sounded happy - from day one.

You have the "cap" thingie already. You don't need the special shroud as you car came equipped with the internal regulator from the factory. I had to do some dremeling on my 81 to fit the internal regulator, which I think was the last year for the external regulator.

FWIW - sounds like your battery is fine, given it's age. The last thing you would think that should last 11 years. Was that one an Interstate? Edit: just read it was. That is awesome performance from a battery.

[mhackney]

Yes, it is an an 85 month Interstate Mega-tron plus 850CCA - part #MTP-91/T6. I'll put it back on the charger tonight and see if it will take a charge. I know I was charging at 2A on Wed night and it was on the charger for about 6 hrs before I shut it off to leave. Given that it was 5AM I may have misread the voltage.

In any case, I can't do anything until next week when the new alt arrives and by then I should be able to track down a battery. I think I'll just go ahead with the battery too so I have a baseline to work from this point forward. I drive 380 mile from Boston to Rochester, NY one to two times a month during the driving season so I need reliability.

[mhackney]

Well, I started the disassembly to remove the alternator today in prep for arrival of the new one. I thought I might have the shroud and fan bead blasted to spruce them up a bit. It was pretty straightforward removing the old fan/alternator. However, Bentley refers to "remove the ground strap from the alternator to the engine" I didn't see that, I only had the 3 wiring terminals on the back of the alt.

Anyway, once I got the assembly out of the car and the alternator removed I noticed several cracks in the fan housing. I actually saw these when I first started the removal since the biggest crack is at the top of the housing.





The fan seems to be fine. It looks like the PO overtightened the alt to the housing and stressed it. What is the best option for replacement? I'd like to maintain originality.

The broken housing is 930-106-102-0R - was that a replacement? My 83 PET shows 930-106-006-00 as the correct part for 80-