At wits end... alternator...

[Sponge]

I need help... after rebuilding my engine I have a very annoying problem I can not clear. The alternator lights is on when the engine is running (Some of the time).

Car: 1981SC with 3.0 and no mods...

Here are the indications:

1. At Idle it glowes
2. Increased Revs = increse in the brightness... slow increase till about 4500 then real bright then out. -- but it does this in jumps
3. Sometimes it is out at idle and most RPM (Starts glowing higher)
4. When it is out, the battery is charging.(12.86).. when it is on it is not (11.7 and decreasing)

The most frustrating part is that it does not do it 100% of the time. What I have tried:

1. Replaced the Voltage Regulator
2. Had the Alternator Rebuilt
3. Replace and check tension on Fan Belt
4. Had battery checked / charged
4. Checked Ground from back of Alt to Engine block
5. Check engine Trans ground strap (It is there, though old, but not frayed)
6. Checked Batt to Alt Connection -- get battery power at back of Alt when Alt is out.
7. Tried to verify all wiring with the diagrams on PP
8. Read all the other charging posts on the BBS and PP

The one positive is that I have gotten good at taking out and putting back in the Fan/Alt...

Additional question... do not know if associated. There are connected brown wires that come off of the wire bundle going out the front of the engine that connects into the plug in the chassis... where do these brown lines connect...

This did begin after I reinstalled the engine - so it could be some bad wiring -- I took great pictures of the engine once out and CIS off, but missed taking some key ones before it was out, and as I removed CIS and wiring harness.

Any thoughts would be appreciated... I have spent way too long on this one issue --

[yelcab1]

Originally posted by Sponge
I need help...

Additional question... do not know if associated. There are connected brown wires that come off of the wire bundle going out the front of the engine that connects into the plug in the chassis... where do these brown lines connect...

--

Those brown wires (two if I remember) are ground wires and are connected to the engine somewhere (anywhere) to provide a ground path for some of the CIS components on that same wire harness.

Lack of a local ground means those components now have to find a ground someplace else that is not as low resistance. It "may" explain your problem.

Find a good clean bolt on your engine, and attach those lose brown wires.

[Sponge]

Right now they are to the #3 Intake bolt... best guess on my part looking at some of my old photos... thanks -- guess that is not it... but will move them to another place just incase... Thanks...

[Lorenfb]

As long as the engine ground strap to the chassis and the battery
have a good chassis grounds, then all grounds are O.K. The case of the
alt. makes an essential ground to the engine, i.e. the brown wires
just assure a good ground if the alt. case is oxidized or painted.

It's possible that the B+ connection on the alt. and starter are not
good and need to be soldered. Also, if your car has the noise
suppressor between the alt. and regulator, remove it and plug
directly into the reg.

Lastly, where did the rebulit alt. come from? Hope it's not from
Joe's Alt. Shop for $55.00.

[masraum]

Yep, you've got a problem, because 12.86V is not really charging. I would expect to see more like 13.5V when charging or even anything between 13 and 14.5. I assume you get the fan belt plenty tight?

Good luck, nothing more frustrating than this sort of problem.

[304065]

Sponge Man,

We are gonna fix this problem right now! Its all about the warning light.

I know you've read everything and you know how it works so I'm going to keep the theory short. Current flows out of the battery, into the ignition switch and to one terminal of the 4W warning light bulb mounted in the back of your oil pressure gauge. The other terminal is connected to a blue wire. That blue wire runs to the back of the car to the electrical console, into the voltage regulator and back out through the 14-pin connector, into the engine wire harness. When you turn the ignition on, the alternator's not putting out any current so the direction of current flow is from the battery to the alternator and to ground. When the alternator is charging, current flows "back up" the blue wire, equalizing the potential difference and the light goes out.

So when the engine is running and the light is ON, either the alternator isn't charging or the blue wire is shorting to ground somewhere along its length.

"When it is out, the battery is charging (12.86)." Pretty weak, though. You should be seeing a strong 14V.

The fact that the light comes on tells you it's not the connection behind the dash, and you verified that you had current in the blue wire when you had the alternator out. The other way to do that is to just touch the blue wire that connects to the terminal on the back of the alternator to the engine case. The warning lamp should glow brightly.

It sounds like you have one of two problems here. Either a high-resistance connection or bad diodes. The back of the alternator has four connections in an externally regulated car:

B+ (at least two, maybe three fat red wires-- two go to the engine wire harness and one goes through the grommet at the forward edge of the engine tin to the starter)

B- (fat brown wire. goes to the engine wire harness)

D+/61 (thin blue wire, the one we have been talking about)

DF (thin black wire, "Dynamo Field" or the field wire, used to supply field excitation current once the alternator is putting out voltage)

Also, you note correctly that there should be a metal ground strap going from the D- connection (alternator case) to one of the engine case parting line bolts.

You are getting a low voltage output, caused by high resistance somewhere, such that the light's on most of the time, and only when you rev the engine up very high does the voltage increase to the point where it's equal to the voltage coming from the battery. I would clean all of the connections on the back of the alternator with emery cloth and some denatured alcohol or electrical contact cleaner. Then you should take a q-tip and clean all of the male and female pins in the 14-pin engine connector at the rear of the electrical console. Is your engine wire harness in good shape? If those wires are brittle/work hardened you could have a bad connection somewhere. You could clean out the 14-pin connector by removing the cap but BE CAREFUL, as soon as you take off that cap ALL of the wires are going to want to come out, and you will need the pin configuration for your particular year to get them back in in the correct order! But you will see the red and brown wires, they are soldered to silver pins, and there may be a broken connection there or some serious oxidation. Also, the wire that runs down to your starter may also be oxidized. Clean the connections on all the wires at the back of the alternator, and you may want to jack and properly support the car and then check the connection on the starter terminal, make sure it's tight. While you're under there, change the ground strap. Those things tend to oxidize seriously-- you want a nice bright contact surface on the trans and on the body.

I'll bet you dollars to donuts that cleaning all those connections fixes your problem. As for the mystery brown wires, can you describe these in more detail? Where do they start, how big are the wires?

The other possibility is that the alternator diodes are bad, but you said it was rebuilt. Not all rebuilding shops do a good job but you can do a search under 'LorenFB" for more commentary on that, he has more experience with rebuilds.

Good luck!

[Sponge]

Ok, thanks so much... Now I have a lot to do -- I am going to go through all of the checks listed above and clean everything that is connected to the system (Including a PP order for a new grounding strap). When I looked at the Wiring Harness it looked in pretty good shape, but I will double check all of the plugs. I will Let you know if it works -- I hope so.

I had the rebuild done by a shop in SC recommended in this forum... don't think that is the problem - especially since it was doing the same thing before the rebuild.

Thanks again --

[Sponge]

The wires I am asking about are in the lower left corner -- the are in the same bundle going back to the rear connection then branch off -- right now I have them grounded to the engine.

Thanks

[kpfoten]

Dunno if this would help, as you had the alternator rebuilt, but I had the same problem and it turned out to be bad solder connections on my alternator...

[jmohn]

Be sure to check all connections (as was mentioned earlier, but you've already checked most of them during the re-install). Sorry to say it sounds very much like failing diodes or bushes, which means another alternator rebuild.

Jerry M
'78 SC

[Lorenfb]

You can easily check the alt. for the most part yourself:

1. the DF pin to the brushes should read 6 ohms to the case
when the shaft is turned (no changing of ohms)
2. if the diode plates were not changed to the older pressfit diodes,
then the diode connections are O.K. (later are soldered)
3. if new wires were installed and not just taped (as I've seen) then
wires are O.K., but still check the soldering of them
4. make sure that all the nuts on the alt. are tight
5. diodes are rarely ever intermittent

As has been said on other posts; Clean and solder all connections from
the alt. to the battery. This is very critical on older cars.

[Gunter]

Is the conection from battery neg terminal to body good? I found this to be in need of a good clean-up since it is out of sight. I removed the bolt, scraped and cleaned all metal and used die-electric grease.

[Sponge]

OK -- after some work (Cleaning and Checking) but with the same indications-- here is what I have.

1. I think the battery ground is good (Cleaned) : I get the same voltage if I go pos terminal to neg terminal or pos terminal to car ground...

2. The connections from the engine to the left side of the car seem to be good (cleaned) and the engine ground spots seem to be good (all checked): I get the same battery voltage when I check from the second fuse down (in the left side of engine compartment) to an engine ground as I do from the battery...

3. The Alt is good: Once you start the car (though the light in the dash is glowing) you get 14.36 (give of take) when you check between the second fuse and all of the engine grounds I am using (including the one I conneted the brown wires I was asking about...).

So, I was not able to jack up the car, but I am guessing something with the starter connection, those wirese or at least the wires running to the light or the battery... Nothing solved, but I feel like I have a better understanding (thanks to the answers I have recieved - thanks) and am closer to a solution.

I was not able to drive the car to check to see if the indications had changed due to the WX , but with the icy mix and freezing rain falling outside right now I am hoping my work will be CNX tomorow and I can reattack!

[rickeolis]

Sponge,
I hope this helps some, because everything you speak of was happening to me, and I fixed it. John Cramer helped me a lot with figuring out what to check and all. So, I took my alternator to a shop to have it tested. It was fine. Then, I used the figures that John listed to check the voltage regulator, it was fine. I then cleaned and rechecked my wires at the alternator and harnesses, all were good.
Finally someone (may have been John) mentioned that the small unit that the wiring harness goes to just before it plugs into the voltage regulator is a radio interference suppressor, and it could be bypassed simply by plugging the harness directly into the voltage regulator.
This was my only problem from square one... the suppressor was bad.

Glad it works now, and hope you get yours going soon.

[PBJauker]

sounds like you have a bad diode in your alt

[304065]

Sponge Man,

The cool thing about 911s is that the use the same cable for the starter that is used to charge the battery. What happens when you crank the starter, does the engine turn over rapidly? If yes, then there's probably not a high resistance between the battery and the starter post. But the way to check is to measure the battery voltage at the battery terminals up front with the engine running.

So you verified that the alternator is charging (good) and you have continuity at least to the engine compartment.

The part that doesn't fit is, the alternator cannot "self-excite," that is, there must be current flowing through the warning light bulb and back to the rotor, to magnetize the rotor, in order to get the alternator to begin charging. Once it begins to charge, the voltage should flow back through that very same circuit and extinguish the bulb. I guess what I'm saying is, it's impossible for the circuit to work in one direction but not in the other.

[Sponge]

John

That is what I thought... so therefore do not understand what is going on -- the Alt does have battery voltage to the back (checked with putting back in) so I figured it had to go back to the battery afterwards.... but oviously it is not. I am going to continue to troubleshoot today (too much ice on the roads for work!!) I was deep into the electical diagrams on tech help pages last night and plan on shooting most of the lines today... thanks for the help --

If the battery is fully charged, then the starter turns over good (not great, good) -- if it is discharged at all (11.6 or so) then it turns over very slowly or not at all... one of the reasons I was going to check starter connections and wires.

Yes it was good news to see 14.4 back in the engine compartment -- Alt is not the problem...

[Sponge]

Fixed!!!

I took the battery and alt wire off of the starter (terminal 30), cleaned them and the post and put them back on. Started the car and there is was -- 14+ at the battery. Tried it at different throttle settings and all good.... guess that was it.

All said and done I am left with a new voltage regulator, rebuilt alt, and a much better knowledge of the charging system.

Thanks everyone for the responses... they helped alot!!

[304065]

Nice!

[Lorenfb]

Don't forget "them" wires from back to front. A common oversight by many
including Porsche shop mechanics.

The best solution is to solder the wire terminals (no crimps) at the alt. and
starter, as the B+ wire carries the full rating of the alt. (> 55 amps).