GregBBRD

If those numbers are with a "heat soaked" alternator (I assume they are, since your problem occurs when the engine is hot, right?), they are absolutely fantastic!

Not many 928's are able to do that.

j.kenzie@sbcglobal.net

Hey, I agree, Greg. But since they were kind of presented as a series of not started, then started then more loads running, I took it that they do not represent heat soaked conditions.
Very important point.
Thanks, Greg.
Dave

merchauser

I took these readings after driving the car for a few hours: is that considered heat soaked?

docmirror

Ignition module? They have a history. The 15 bus goes through there, also part of the 30 bus I think? Yes, an hour or more driving, the alt is heat soaked.

Moving the goal posts - not fair.

Jason89s4

If you did the tests within 10 minutes or so of driving around for a few hours, the alternator it may be "heat soaked". Otherwise it will cool down before you have a chance. Diagnosing whether an issue is due to heat soak can be tricky, since as soon as you open the hood you are releasing one of the causes of heat soak, which is the trapped air.
However, as the others have said, your voltage readings look very strong.
Generally, it is hard to diagnose "random" issues when the car is parked and the condition is not presenting itself. (I know this doesn't help, but its just the reality of randomness.) Did you mention that your voltage drop symptoms ever happen in your garage, or only when driving?

merchauser

"they have a history" meaning, they are akin to a wear item and need periodic replacement?

"the 15 bus goes through there, also part of the 30 bus" not sure I understand relevance or meaning?

and today was the first time in over 2 years, that my car stalled in cold conditions; although, after driving this AM for a few hours, and this afternoon for a few more, car would not stall
while AC, and loads were present??

merchauser

the only time I was able to replicate the stall in the garage was last week when I was recharging the AC (outside in the driveway with 85'). I was holding the car @2k for a few minutes, and releasing the throttle immediately stalled the car. started the car, revved it up again, and stalled again. when recording the volt readings today, I tried to replicate, but could not get the car to stall??

regarding ignition control module, would it help to clean up those connections and hit them with deoxit or do these modules get finicky?

docmirror

The ignition switch has some history of failure modes like you describe. Unfortunately, I don't have any test procedure for it, except replacement with a new or different electrical ignition switch asm. Me and a couple guys fought with an 87 that had a switch issue for a few hours.

The two primary power buses in the 928 are the 15 and 30 bus. Obviously, the primary power bus has to go to the ign switch so that all of the features that can be run from start up, to running will trigger off the turn of the ign switch. The 30 bus has power any time there is a battery present in the car. The ign switch delivers power to the 15 bus which then distributes power to the various circuits that make the car run. If the key is turned to start, and the starter turns, when you let off the key, it is in the 'on' position, and power goes to all engine running circuits via the 15 bus(and in some cases, direct, and in some cases via a relay or fuse or both). A fault in the ign switch could shut off power to the running circuits of the car.

merchauser

doc, I thought you were referring to the ignition module(s) in your earlier post (#64)? did you mean the ignition switch?

docmirror

Oops. Ignition switch.

merchauser

ok, that's a horse of a different color: not sure I understand how the ignition switch would create the symptom I am having? would it be a good idea to get in there and clean the connection contacts, or is the problem you refer to internal to the switch?

j.kenzie@sbcglobal.net

An ignition switch can turn off your ignition. It can be unpredictable. If it stalls or misbehaves, you could try jiggling the ignition switch. Not definitive, obviously, unless it restores function on several occasions. The switch is known to be problematic. It tends to be off or on, not in between.
Good luck,
Dave

merchauser

dave, my eyes and ears are always open to suggestions, especially when great info is distributed by those with incredible knowledge. that said, I just don't see how my ignition switch could be at issue. I have had other cars with ignition switch issues, and dealt with the jiggling, and most often, they are pass or fail items. I started going over as many grounds that are accessible, in an attempt to put those off the table I have an unsubstantiated hunch that my battery ground strap (original) could be the culprit. the new one will be here on Wednesday.

but my mind is wide open to other thoughts.....

j.kenzie@sbcglobal.net

Yeah, you're probably right. Your problem sounds like a voltage regulator that sometimes works properly, and sometimes does not. The ignition switch was brought up, so I wanted to explain that they often fail, intermittently. It does seem unlikely that this would cause variously low voltage problems. I did have an alternator that seemed to have one bad diode, which when replaced gave me back an additional 1.5 volts. Maybe some such item is starting to die on yours. Mine failed gradually, then constantly, before repair.
Good luck,
Dave

Jason89s4

Tend to agree that my experience with ignition switch issues is a pass or fail proposition. Not a slow voltage "death" like merchauser is experiencing sometimes.