drscottsmith

All -

1983 US model. I have been experiencing sporadic charging and today culminated in a dead battery. Most times, the car starts and the gauge reads just above the bottom white line. All motorized accessories are very slow (e.g. windows, blower, wipers, etc.). After a couple of minutes, the gauge generally jumps to about 14 and everything is back to normal. The actual amount of time varies. Sometimes a quick blip of the throttle kicks it in.

Note: I never get the red charging light at any time, other than when turning the ignition on to start the car.

Today, the gauge never jumped to 14. I had stopped to drop some materials off and the car would not start back. Still had enough juice to run accessories but not enough to crank car.

Any particular charging related problem based on these symptoms? My initial thoughts are alternator brushes or voltage regulator.

Thanks -

-scott

Speedtoys

Can try the VR first, cheap.

skpyle

Hey Scott,

About all I can offer for the moment is to verify the readings at the jump post. I trust the gauge about as far as I can throw it.
As well, verify you are getting the excitation signal to the alternator. if I remember correctly, look for 12VDC or greater on the blue wire at the back of the alternator.
A quick and dirty way to check is to pop the top of the 14-pin connector. If I am reading the diagram correctly, T is the 14-oin connector, and 1 is the pin. So look for the blue wire there. You can check signal there easily.
Refer to this snippet of the 1983 US Current Flow Diagram:


Blue wire is excitation wire for the field controlled by the voltage regulator.

skpyle

WSM is relatively useless for alternator troubleshooting.
I found these in a separate 928S Electrical Troubleshooting & Repair:

dr bob

Do you have the original alternator, or has it been 'upgraded' to a Bosch? Reason I ask: The early alternators didn't need as much excitation to get charging started. Replacement, especially later Bosch units, take more. There's a bulletin that sez you will need to change a resistor that lives in parallel with the charge light bulb in the cluster.

There's usually enough residual magnetism in the alternator armature to get charging started once engine speed exceeds 3000-3500 RPM even with low external excitation current. Once charging starts, the alternator is self-exciting via a diode inside. Try revving the engine past 3500 and see if the voltage jumps to closer to normal. If so, you'll want to consider checking the excitation path from the cluster through the CE panel and the 14-pin as Seth describes. The charge light on with initial key on suggests that the path is intact though. From there, you can do some resistor replacement on the cluster circuit board. If the voltage doesn't come up after the 3500 RPM tickle, another alternator may be in your immediate future.

edit: Seth found the relevant electrical guidance, including how to test for sufficient excitation at the alternator terminals.

GregBBRD

The 1983 model has a very narrow multi-groove belt. (Two years only). Very prone to slipping, especially if the battery is low to start with. This belt needs to be kept in very good condition (soft) and tight to function. New belts of this design stretch a bunch and if you don't retighten them after running them a couple of times, they will slip and be ruined. The battery needs to be maintained with an external charger, if the car sits for more than 3-4 days.

jpitman2

Mine died like this last year - alternator charge was dying off as the temp went up - 20 mins stationary idling voltage went from 14.1 back to 12.2, ie, no charge. Try that test. Leaving it on trickle charge masked the problem until I tried to do multiple restarts without a charge. New alternator fixed it. Valeo unit with a 928 number on it.
Attachment 1343783
jp 83 Euro S AT 57k

drscottsmith

Well after testing and some additional research, it looks like my issue may be related to what dr bob mentions...as well as info posted by Matt de Maria...

the ‘charge’ light does NOT always come on with ignition as I initially reported. I verified all of the connections at the CEP and cluster, and checked belt tightness as well.

now I am back to the issue where the alt will not start charging until I blip the throttle to about 3k rpm - then the gauge springs to life.

so... some additional information:
1) car has lutz circuit boards behind the cluster
2) not sure if alternator is original or not to car
3) car has 119k

next step will be to verify output at alternator and update thread.

thank you all-

​​​​​​—scott

dr bob

Scott --

You can verify excitation circuit to the alternator pretty easily with your DMM. With access to the rear of the alternator (cover unbolted and slid down the cables a bit...), use your volt meter to verify that there is some excitation voltage reaching the alternator with the key on but engine not running. In this condition, the charge light in the cluster should be illuminated and there should be some voltage showing at the excitation (smaller...) terminal on the alternator. I didn't do the voltage drop calc through there because I don't know which alternator you have. Regardless, there should be something greater than maybe 4 volts and less than battery voltage in that configuration. If you see voltage there but the charge light is not illuminated, jumper that same excitation terminal on the alternator to ground. Then same test condition with key on but engine not started, the charge light should be glowing bright. If you saw voltage but the lamp isn't lit, the bulb is probably failed. If you saw no voltage and the lamp was lit, lift the terminal off the alternator and test again just to the wire. If you see voltage there, the regulator is shorted. If still no voltage, there's a failure in the wiring or a connector between the cluster and the alternator. Seth's diagram shows all the connections, starting at the 15 bus on the bottom right (on with key in run or start) and makes its way back around through CE panel and cluster connections, through the bulb and the parallel resistor, then out of the cluster to the CE panel again in several places, finally to the 14-pin under the hood, the front of engine harness, and finally to the D+ excitation terminal on the alternator. Most Frequent Failure Points are between the 14-pin and the alternator, and the 14-pin connector itself, if that helps.

jpitman2

Good luck loosening the rear cover on the alternator while its still mounted! BTW, what are 'lutz' circuit boards? Doesnt this sound like the warning bulb is dead?
jp 83 Euro S AT 57k

drscottsmith

Lutz circuit boards are the replacement hard circuit boards that roger sells - they replace the factory plastic flexible circuit board. LEDs are built on the board for telltales. It does have the resistor across the voltmeter terminals however.

so I just went for a drive and noticed a couple of new things -

1). The Charge light came on every time I started the car (even after a couple of stops). It also kind of ‘dims out’ when you turn the ignition off.

2). During most of the drive, tha gauge read higher (right at 14v line) than it ever has. Typically it rides just under that line once it gets excited.

i did notice a couple of times it dropped to that lower level, but by the time I looked at the road and looked back, it was back up to 14.

i know the gauges can be flaky, but have always been of the mindset that gauge readings - especially those like our cars that read in real time and fluctuate based on dynamics - are relative to the car. So if my oil pressure typically reads 4 bar after a 40 mile drive but then all of a sudden we’re to read 1 bar in the same situation, then I have an issue somewhere.

still plan to test the regulator and exciter on the alternator. I have had that cover off before and it was not fun mounted on the car!

-Scott

dr bob

Scott --

The readings and particularly the charge light "kind of dims out when you turn the key off" would have me sleuthing some more. Test that exciter connection at the 14 pin, but just carefully lift the cover off the connector so you can get your meter on there. With key off, that definitely needs to be zero voltage potential. "Dims Out" implies to me that there's some current still flowing through that circuit even with the key off. If there is in fact even some minor voltage there, find out whether it's coming from the car or the alternator ends. A failing excitation diode in the alternator or bad regulator are likely causes.

Shark2626

If you are trying to find out which is giving you the issue, the alternator or the gauge, why not start the car and test the voltage at the jump post with your multimeter? That will tell you what voltage your alternator is putting out and will rule it in or out for you. Maybe that’s too simple, but it worked for me.

drscottsmith

I always say a pic is worth 1000 words...here’s a video of the issue...

drscottsmith

Shark2626:

meant to post that earlier...readings at jump post are:

idle no accessories - 14.2v dc
with head and fog lights on - 14.08 v dc
with all lights and ac on - 14.0 v dc

-scott