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Bill I am gonna venture a guess that What Greg is pointing at is if your LH is original and you find that you need a jump to get the car started,
or some other booster system is added to your depleted battery, in an effort to start the car.
NOTE the possibility is greater that an electron spike will damage your LH computer., or alternator or diodes, or any other of the many electronic boxes in the car.
FWIW My 1988 S4 had a fresh rebuilt LH and then shortly after this was done,
the PO mechanics added a new non Bosch regulator to the alternator, probably due to worn brushes.
Since it was a new part they probably only checked this alternator output once .
By the time I got the car the alternator output had risen to 18.7 volts at the hot post. This indicated a failed regulator.
This created a few differing effects on the operation of the car, I noted that fans would turn on without any activation. and one or the other fan would run
The alt gauge would not move, it seemed like it was stuck at the off position,
the engine would not accelerate , only stumble and die when the throttle was pressed.
.
Anyway I was still trying to find out what was causing all of these strange things to occur and my answer was in a voltage test.
I checked the charging voltage at the hot post, and it was at 18.7V the highest charge I have ever seen.
What I found out later was that The freshly repaired LH would allow the engine start and idle,
but the acceleration circuit had been damaged from the over voltage condition.
I installed a new Bosch regulator then started the car,
the charge voltage began reading 14.2 V .
I then swapped out the freshly repaired LH for my spare,
the engine started up rough and stumbled for about 30 seconds then like magic it went into an even smooth idle.
I hit the gas and the engine responded immediately, it ran perfectly.
So All I have to offer here is what the WSM provides on warnings for the electrical system care and operation,
I will always caution the caretakers to exercise caution when it comes to boosting a battery in a 928.
NOTE if your charging system is only outputting 13.4 v or less then the chances are very good that you have a failed diode,
alternator damage can occur when trying to run a car with a low battery and adding a booster to the system, this can tax the diodes and damage them.
If you have never had an issue with your 928 charging system then you have been lucky and it has not cost you anything.
By heeding this advice you will prevent seemingly unrelated systems from being damaged.
For me its always best to charge the battery disconnected, and given a choice I'd always do that. But if the battery is low but not fully dead and I know it was recently drained by accidentally leaving lights on etc I'd connect another battery without worry (but not a running vehicle) in order to start the car (e.g if far away from normal support methods). I'd leave the extra battery connected for a while (~2 mins) after starting - then all should be good to go (check charge level more fully later).
This would not be my preferred method but I think its a relatively safe thing to do it this way if in major need.
However don't attempt this if the battery is fully dead - you really don't know what you are dealing with and it could be quite dangerous. Don't ever use a 110V/220V charger/starter on the battery while connected to the car - this can easily fry things - as can using a running car for a boost - where: when you disconnect you can loose all regulation if the battery is actually totally shot or OC).
Be very careful when connecting batteries - many horror stories. Batteries can even explode quite quickly if seriously abused - an exploding battery is a very serious deal.
Sure, jumping from another car or other source with unknown voltage output sounds like a bad idea, but that's not what I asked. Several here seem to be suggesting you have no option other than removing the battery from the 928 electrical system and charging it. I still go back to Jim Corenman's explanation of what is safe and not safe. I can't see a problem with using a voltage regulated battery jumper.
Sure, jumping from another car or other source with unknown voltage output sounds like a bad idea, but that's not what I asked. Several here seem to be suggesting you have no option other than removing the battery from the 928 electrical system and charging it. I still go back to Jim Corenman's explanation of what is safe and not safe. I can't see a problem with using a voltage regulated battery jumper.
+1
I try to never leave the house without one of my jumper packs in the car.
Talk to any repair shop, most have multiples lined up like little soldiers ready to jump start a dead car in the parking lot. If such things were blowing up ECU's they would be frying one a week. Anyone who thinks a 928 electronics are fragile, they haven't worked on a late model BMW.
Electrons appear to be poorly understood by many of us, and I am no physicist, but 12 volts is 12 volts. I was puzzled when the WSM reference was made earlier, and I coudn't find anything when I looked. And certainly many have had bad experiences with accidental gross overvoltage conditions like the one MrMerlin describes and Greg's post, and certainly old LH tile chips blow like popcorn, and aftermarket parts + inexperienced mechanics/owners can break things.
But jump starting is a standard procedure for all cars. When I finally decided to RTF 1991 S4/GT Owners Manual it is crystal clear: Jump starting is fully supported by Porsche with the caution that the second vehicle should not be running and the explicit sequence of connections be observed. Further, the "jump post" is exactly what you'd expect with that name, or in Porsche nomenclature the "start assist remote terminal." So at least for MY1991 go ahead and use your external batteries, whether on another car or standalone jump packs, and connect them to the jump post and an engine ground.
If you have a problem you can always file a warranty claim.
Finally finished replacing the bearings in my '78s torque tube which included installing and removing the clutch 6 and 1/2 times! I left the trans and engine in place so getting the drive shaft out of the transmission was challenging and getting the torque tube back in place was challenging. Getting the bearings out was comparably simple.
Electrons appear to be poorly understood by many of us, and I am no physicist, but 12 volts is 12 volts. I was puzzled when the WSM reference was made earlier, and I coudn't find anything when I looked. And certainly many have had bad experiences with accidental gross overvoltage conditions like the one MrMerlin describes and Greg's post, and certainly old LH tile chips blow like popcorn, and aftermarket parts + inexperienced mechanics/owners can break things.
But jump starting is a standard procedure for all cars. When I finally decided to RTF 1991 S4/GT Owners Manual it is crystal clear: Jump starting is fully supported by Porsche with the caution that the second vehicle should not be running and the explicit sequence of connections be observed. Further, the "jump post" is exactly what you'd expect with that name, or in Porsche nomenclature the "start assist remote terminal." So at least for MY1991 go ahead and use your external batteries, whether on another car or standalone jump packs, and connect them to the jump post and an engine ground.
If you have a problem you can always file a warranty claim.
Note it doesnt say to unplug and remove the ECUs to a safe undisclosed location.
Decided this Mother's Day to try the new floor jack, correctly on the driver front jack point - simply to look at the oil filter and plug. After lowering, I quickly noticed the shocks did not lower the front fender, quite jacked-up look. Hmmmm.
Anyone have any views on "peak amperage" limits for a jump starter without frying anything in a 928?
I'm of the view best to charge/repair a battery that has sat first and foremost and not to jump start.
But I want a portable jump starter in the Shark just in case.
"peak amperage" seems to be the measure to watch more so than MaH or AMPs?
10-03-2019, 05:12 PM
