Alan

Tim - you need to take it to a place that specializes in alternator rebuilds. They should have a load bench setup that can run for a while with a current load on the output and monitor voltage & current - I very much doubt Autozone does more than a very cursory & brief check.... its not going to be enough for this case.

Alan

85fortheDrive

Okay, I did this this afternoon. The Bosch alternator was put through five minutes of intermittent loading. It fed a steady 14.3V the whole time.

So at least during that more thorough bench testing, this remanufactured alternator seemed okay. I am truly curious about the possibility of a grounding issue here. The guy who ran the test (his name was Dusty - really) suggested that an alternator will mistakenly crank out more volts if it thinks the battery is dead. There is no battery wire run to this type of alternator, but a problem ground could cause such a mistake. The fact that the spiking happens most commonly in wet weather conditions has be wondering if there is wiring insulation issues somewhere. Within the main wiring harness maybe?

Ready for the next test. I'm open to all suggestions

Continued thanks...

Alan

Well its hard to imagine the alternator isn't well grounded the way its bolted to the block. So that would leave the battery ground or battery supply if there is any chance it disconnects.

This can cause erratic voltages or spiking but usually not to the extent or stability that you are seeing.

I understood you had already replaced the battery and ground strap - which seemed to rule that out.

One option is to run leads to the battery posts direct and back to your DMM located where you can see it.. then see if you ever get a case where the DMM says ~12.8v and the car gauge looks like 16-18v. That would be very interesting...

Usually when you have any issues with the battery not providing enough load/store to stabilize the regulator it also shows up in very weak starter cranking - or occasional failure to crank at all... have you experienced this at all recently?

Alan

85fortheDrive

Both the engine and battery ground straps are new. To be clear, however, the new battery is so short that the OEM battery ground strap did not reach to the wingnut groundling location in the back hatch. So I bought a third party strap for this purpose. Seems to work okay. Only drawback is that it is a round cable, not a flat strap, causing a little cockeyedness in the tool panel when it's inserted.
I'm guessing that would isolate the problem to the alternator. But I'm still curious about voltage leaks within the wiring harness and at the jump post. If water was getting into the circuitry, could that create an unwanted ground and then "pull" more voltage from the alternator? Same way that a dying battery might cause such a pull?
Nope. Car turns over just fine all the time.

Alan

No if this is happening it would mean the battery is getting disconnected from the alternator while you are driving. This would have nothing to do with the jump post since its after the battery connects to the alternator.

See if it happens... if yes it questions the battery itself, the battery ground strap to the frame, the engine ground strap, the battery feeder to the starter or the starter to alternator connection. much of this is newly replaced...

If any of these other than the starter to alternator connection were intermittent - the car would not start reliably...

It does throw suspicion on that starter to alternator connection - but its actually usually a reliable one...

Check the smaller connection to the large stud of the starter motor - clean the ring terminals well and assemble tightly... similarly check the alternator connections - are all of them clean and secure to the alternator large stud.

Alan

85fortheDrive

March 30 update:

Dave McKenzie assisted me with the reinstallation of the alternator yesterday. In doing so, he noted that the ground wire that splits off of the alternator cabling bundle and connects to the oil pan was unplugged from its connection point. This wire is extrememly brittle and and I tried to repair it when I was replacing the oil pan gasket.

We crimped the female connection end of this wire and Dave snapped it back on to the oil pan connection.

This morning, I took the car out in slightly damp weather. On its third start, the voltage jumped to 16.6V for about 10 seconds and then settled back to 14.2V.

I will reinvestigate the connections between battery, starter, and alternator. I thought that, after start-up, the starter no longer factored into the electronics. But I'm reading Alan to say that if the wiring between the started and alternator is compromised, the alternator can think that the battery is not working and then possibly elevate its voltage output.

Continued thanks.

85fortheDrive

Okay, I tested this tonight. Weather is rainy again - ideal for the investigation.

Connected DMM to battery posts. Started car from cold and gauge briefly rose to 16. DMM also read 16. Twice more the gauge spiked and the DMM spiked with it. Thus, the battery was putting out the increased voltage as well.

Restarted the car a couple times after taking it for a brief spin. Most of the time, the DMM read 14.2V.

In the last trial, I waited about 10 minutes to restart the car. Upon start, the gauge dropped to 10V. The DMM read 11.97V (with the headlights on). Drove the car for about five minutes and the voltage never returned to normal.

So does this prove that the alternator is funky?

Continued thanks to Alan and Roger!

j.kenzie@sbcglobal.net

Tim and Alan and other electrical guru's,
It seems to me the problem here is voltage spikes. I've heard that if you disconnect your battery while the engine is running (WHICH YOU SHOULD NEVER DO) you will cause voltage spikes. Is there a way that something could be causing a poor connection to your battery, making your alternator think you are disconnecting the battery?

85fortheDrive

Let's make sure that we have our taxonomies correct here. I do not belong to this phylum. Alan does, for sure!

Thanks to you guys, I am learning, however.

Mrmerlin

Please reinspect your hot post connections with battery disconnected . this will include removing the 11mm securing bolt and then opening up both sides of the 14 pin connector. You will be looking for shredded/crumbling wire insulations , make a diagram of the wires positions so they dont fall out whilest your working on the connector, Look down the black insulation and see if the insulation is good here as well you may need to install some heatshrink on the fouled up wires, and clean everything with a pink eraser and then install the hot post cover for a 88 S4 dont let the car get wet till your hot post cover is in place

Alan

Tim - The battery serves 3 purposes:

1) Start the car - provide power to the starter and ECU's before the alternator starts generating.
2) Serve as a stabilizing load for the alternators regulator to maintain stable voltage
(and meanwhile recharge to be ready for Job 1 next time).
3) Serve as a backup power source under high electrical load & low rpm conditions (where the alternator may not be able to generate all the power needed - should be a very rare occurrance).

Tim is not seeing voiltage spikes - he is seeing consistent substantially elevated system voltage. Voltage spikes are characterized as very short duration (in the case of an alternator usually related to the field rotation per phase) and not a high rms value. Clearly we aren't seeing that here and we know there is a good connection to the battery.

I told Tim in a PM that battery - internal damage - is also a possible issue but seems umnlikely since I believe it is new since ths problem surfaced.

The jump post doesn't figure in the connection of the Alternator to the Starter to the Battery - which in any case we know is good...

The alternator exhibits both poor regulation (stable high voltage) and failure to initiate some of the time. Whilst there could be several issues together - the Alternator is the most suspect here and much of the rest (even the alt) are new...

I suggested some tests to Tim - ideally the alternator shop could test his alternator and battery together...

Alan

Mrmerlin

please check the 14 pin connectorat the hot post for damaged insulation, alternator wires go through this and this could be part of your problem.Battery disconnected.
Make sure to get a hot post/14pin connector cover( from the 88 S4) after your done and dont let the car get wet till you do

85fortheDrive

Merlin:
I've already begun this cleaning, following your earlier post. Took snapshots of where all the pins, both male and female, go. There is only minor corrosion here, though a little eraserheading might help. I see no apparent wiring damage here, but will inspect more closely.

In the meantime, my main man Roger Tyson is sending along another alternator. One by one, we'll eliminate variables and get to da bottom of dis.

Thanks for your suggestion.

Tim

Alan

Whilst its not a bad general idea to keep this clean - the test was done monitoring battery post voltage directly - and this goes to 16V too....

Thus the battery is connected at all times... lets not go in circles here... cleaning the battery posts would make more sense.

The only possible battery connection fault given the measurements taken is an intermittent internal open circuit - this would certainly also manifest in a no-start condition at least some of the time - but apparently does not...

Tim - you did have the DMM connected directly to both the positive and negative battery terminals directly right?

Alan

85fortheDrive

Finished scrubbing the male bullet plugs tonight and restored the 14-pin connections. Should be good and clean now.

Yes sir, just as you suggested. Tis dry this evening, so I'm gonna take the OB out for a little spin again.

Thanks.