Stranded - need diagnosis help

[tedder]

coming into work this morning after 18 highway miles I was driving in the city and the following started to happen;
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1. Stereo cut out and stereo lights flickered. Headlights seemed fine. Pulled over and turned off the engine to look and saw nothing explaining it (loose faceplate etc)

2. Tried to restart, battery nearly dead (after 18 miles on highway). Just caught on 3rd try.

3. Continued down the road thinking better take the P-car home in case battery won't restart again and it starts lurching.

it would idle, but trying to accelerate, put load on the engine and it would start to die. Headlights now fading. Turned off the lighrts and slipped the clutch to limp to the garage at work and several backfires occurred.

0. about a week ago, the alternator light came on when I started it for about 10 seconds then went back out. I had meant to look into it but had it checked last fall when I put in a new battery and the mech said it was OK.

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So I am thinking that at the least my alternator must be bad and not properly charging the battery (over the winter and early spring it was always on the tender when not in use) but would this account for the inability to sustain a load? Maybe the battery could provide spark for idle but no more?

The only work done on the car recently was when I pulled the A/C compressor off 2 weeks ago.

Any ideas?

Also, the car has been lowered (PO) quite a lot, should I insist on a flatbed to tow it if it doesn't run when I return to it this afternoon?

Arghhhh!

[lateapex911]

Warrren will know all the answers to this one. It does indeed sound as though the issues were caused by a lack of voltage. Odd that the gen light didn't illuminate. IIRC, there should be some warning indication should the bulb fail.

I would charge the battery, and restart. Once it's running, check the voltage with a Volt/ohm multimeter. If it's 14 or so, start checking grounds and connections. If it's battery voltage, get ye to a shop, or do the alt/volt reg diagnosis and repair (with out help, of course!) yourself.

Depending on how far your shop is, you may be able to get there on a fully charged battery, should you decide to let pros handle it..

[tedder]

my big fear is that after borrowing tools and getting the battery charged it'll star but not run. When I have had cars with weak charging before, I could usually keep it going by keeping the revs up.

This time, it wouldn't rev past 3k and not past 1500 with a load on. I forgot to mention that with the pedal down about half way it would surge as well.

Does this still sound like voltage?

[Christien]

I had a similar issue recently with my 944 - died on the highway after about 30 min. of driving. Turned out to be a bad voltage regulator combined with some dirty grounds. A new voltage regulator (cheap) and a cleaning of the grounds and the problem was cured.

[ChrisBennet]

If the voltage is too low the DME (engine computer) won't work.
It sounds like the regulator (on/in the back of the alternator) has "walked towards the light".

-Chris

[tedder]

Is it possible that the voltage regulator prefers it cold?

I just went out to pull the battery to get it charged. With the tools I could scrounge I couldn't get it out (What holds it in place?). So I figured I'd try once more before I accept delete and, after about 2-3 hours sitting, it starts right up like there was no problem.

Drove it home, did some full throttle 3->6.2k rpm runs and it felt just like normal.

Left the PCar at home and came back in the honda. I love my Porsche, but I trust my Honda...

[yelcab1]

I had a dead battery due to a dead alternator once, and the "idiot" light never came on. The ever trusty Digital Volt Meter was right on, no voltage from the alternator, go figure.

[LakeCleElum]

Pull you Alt and have it tested, Internal regulator, so replace it all if bad.....

[Grezdlitn]

I'll take a stab at this one. Hope this makes sense.

If you are able to start the car, measure the voltage at the battery terminals with a multimeter set on AC current. If AC voltage is present then there is a good chance one or both of the diode packs in the alternator is defective. Only option is to have alt rebuilt.

Another test......remove belt that drives alternator. With engine off but key in run position try to rotate alt pully. If you feel resistance then none then resistance again (as you rotate it) then field coils are good and you should look elseware for problem. Perhaps a broken charging wire or a bad ground connection.

Good luck,
Mark

[rick-l]

Sounds like you will be stranded several times until you get this sorted out.

It sounds like your alternator/regulator is not doing it's job. If the brushes are worn to the point they don't make contact the alternator light will not light and the alternator will not charge the battery. Could they be worn right to the edge and not making contact all the time?

[RV Flyer]

Mark, I think you should have recommended a visit to the AeroElectric list, for a review of internally v. externally regulated alternators, OV protection, failure modes, etc. etc. . . . . (Sorry, Pelicans, just a bit of inside humor for us RV drivers....).

This problem reminds me of an experience with my 911 a year or two after I bought it, which I guess would be about 1987. Had the clutch replaced with the 1974 style unit by a reputable Porsche shop in the Seattle area. A week or so later, I start getting a weak battery, alternator light flickering on, etc. Could not track the problem down.

Then, a week or so after that, I'm going across the floating bridge on Lake Washington with my girlfriend (now wife), and there is a horrendous clanking noise and loss of power to the rear wheels. I manage to coast into the only pullout, at the center of the bridge, and look under the car to see a half-shaft laying on the ground, disconnected at the inboard end.

Yup, the idiot mechanic had not tightened the axle bolts - time for a tow truck. And what else did we find when we looked into it? The same hairy (or maybe hairless) ape had neglected to put a nut on the starter stud where the positive cable from the battery hooks up, so the connection there was loose as hell (the cable had to be removed to do the clutch job, of course).

New nut on the stud, tighten the cable, and charging problem solved. New axle bolts, and power again flows to the rear wheels. The shop owner was not too impressed, and was profusely apologetic.

So, just a wild guess, but maybe a loose ground or positive cable, especially if anyone was working in that area recently. . . . Good luck!

[scottb]

I had the identical symptoms. Exactly. It was the alternator. Pull it out and take it to a local rebuilder for testing. I had a foreign alternator shop rebuild mine for about $80, and two years later it's still going strong.

[petrolblue83911]

Had identical experience as well, -the alt light going on when you start it, and then going off when you drive away/rev it a bit=bad alternator in many cases.

[tedder]

after all the rain up here in MA last week it took a while to get to testing the voltage last night. Sitting in the garage with the wife pushing on the load pedal I measured the following voltages at the battery terminals

engine off: 13.4 vdc
1000rpm: 12.68
2000rpm: 12.64
4000rpm: 12.68

I didn't reread this thread first so all voltages were DC. I'll try again tonight checking on AC.

I would have expected that the voltage would go up with RPM if the alternator were working. Am I right about this or can I assume that the alternator is toast?

What other test should I do before I buy a new (rebuilt) alternator and take the Pcar off the road?

[scottb]

It's DC...don't bother checking AC.

It's your alternator or regulator. Pull it and have it rebuilt.

[Grady Clay]

tedder,

I just helped a local Pelican through this.

First, can you put a charger on the battery all afternoon?
That will get you home this evening.

Yes, you should use a flat-bed whenever possible.

You will need a multi-meter (cheep analog works fine).

After you have charged the battery, check the (DC) voltage
with the car not running yet. Should be 12.8 – 13.4 VDC.
Turn the key to the “ON” position. Does the alternator
light come on? Please report.

Start the car. With the rpm>2000, what is the voltage?
Is the voltage creeping up or down? If the voltage is
around 14 VDC and increasing, the alternator is working
and charging the battery. Did the alternator light go out
as the rpm came up? If the voltage is 12.x and decreasing
there is a problem. Please report.

If the alternator is working, the problem is possibly
intermittent (harder to find).
If it isn’t charging it is easier to diagnose. Don’t pull
the alternator yet – just keep the battery charged.

How old is the battery? Our local Pelican’s was 8+ years
old. If in doubt, summarily replace it. Old batteries can
have a myriad of symptoms that can lead the diagnosis
astray.

Checking and cleaning connections is your next step. At
the battery is the first place to look. Clean the battery
and cable terminals. Make sure the terminals and wires
are clean and tight. Check the screws (and fuses) at the
fuse panel. Check & clean the transmission ground strap.
Check the connections at the starter (best done with
battery ground disconnected).

Wire your volt meter to the cigar lighter so you can watch
it while driving. This is particularly useful when chasing
an intermittent problem.

Only after you have done the above, confirmed the alternator
light works and confirmed the alternator isn’t charging a
good battery then remove the alternator. As you get the
fan housing partially out; check the alternator-to-crankcase
ground strap. As you get the air deflector off the back of the
alternator; check that the wires are clean and tight. If you
find a obvious cause, reassemble and test.

An “auto electric” shop can test the alternator out of the car.
The best solution is to exchange it for a rebuilt alternator.
Our host has those.

Before exchanging your alternator, measure the depth of
the alternator. It is best to get the replacement alternator
first before returning your “core” to compare this dimension.
This image is of a Bosch alternator but the issue is the same
for all (SEV Marchall, Motorola). As the alternators became
more powerful, this dimension increased and the fan housing
changed to accommodate the increased depth.



© Dr. Ing. h.c. F. Porsche A.G.

Be very careful to not mislay the nuts off the back of the
alternator, they are hard to replace.

Some Pelican searching on fan belt adjustment will prevent
issues from arising.

Please report back on the diagnosis progress.

Best,
Grady

[tedder]

Grady,

thanks for the long note. The 'stranding was about 2 weeks ago, just responding back to the old thread since I hadn't done the testing until yesterday. From my previous post you can see that the voltages are

not running: 13.4v
any rpm: ~12.6v

The battery was new last November and while the alternator light came on once a few months ago, it hasn't repeated. Looks like the alternator is bad and the alt light didn't really do its job. Oh well, since I did manage to limp home it didn't cost me anything but stress.

Next step will be to get a new alternator from our fine host. Since I'll be away most of July it probably won't go into the car until fall. In the meantime it'll be short trips and back on the battery charger whenever I am home.

Thanks

Ted