erratic battery gauge

[PC-85-928S]

I recently had the "no start" problem with my 1985 928s US version.
I replaced the battery ground, and the engine to body ground on the under front passenger side.
No problems since, good starts, and all lights seem solid and strong.
However lately my battery gauge is very bouncey, and often reads discharging.
Any suggestions?

[Mrmerlin]

remove the alternator from its mount ,
dont let it hang on the harness tie it up with a coathanger.'
Remove the rear cover ,
then the regulator,
inspect the brushes

[bmk928]

Had the same problem in my 80 euro. Ended up being a loose charging post on the passenger fender well. Only figured that out after it fried the alternator.

[PC-85-928S]

i removed the battery cable at the wing nut.
It already had while corrosion starting to build on it.
The washers also looked cruddy.
this cable is only a few months old

i cleaned the connections and reattached, removed the washers.

started great, and the battery gauge is steady in the middle

the rear hatch area seems to get a lot of moisture.

I am thinking about a way to better protect the rear ground wing nut area.

[riber.bentsen]

Fluent wire insulation in a spray can

It's nasty stuff, but it keeps out the moisture..

[PC-85-928S]

i was thinking about this:

NEW 8 FL OZ DIP & GRIP BLACK VINYL COATING FOR TOOLS! - eBay (item 310271925104 end time Nov-24-10 17:19:08 PST)

[JhwShark]

Home Depot sells liquid wire insulation, similar looking to the tool dip. I use it on crimp connectors to seal the ends on the connectors where shrink (heat) fit insulation ends...works fine...brush it on like thick paint.
Jon

[PC-85-928S]

does there have to be washers on either side or the ground cable?
i removed them both because they looked corroded.

do they have to be a specific material, because the cable end looks copper

[PC-85-928S]

Parked it last night, when I started it later all warning lights stayed on.
Even the central warning light was flashing, indicating low oil level.
I did drive it home, and it seemed ok.
I am feeling it is time to have my alternator rebuilt.
I was looking on line to see the cost of a new rebuild.
Does anyone know the correct Bosh replacement for an 1985 928S US (5.0)
Is it 130 amp or 115A?

[JK McDonald]

Hey PC-85-928S, There are a couple of threads that I've seen where some 928 owners have replaced their original alternator with a high output Chevy (Camero ?) unit. If you are not a Bosch purist, it is a nice update for considerably less money.

I'd suggest that you check out all the wiring that goes through the rectangle connector plug on the right passenger side fender well to verify that you do have an alternator issue first.

If you do have to change out the alternator, I am sure someone can provide all the Chevy spec's on exactly what is involved.

Good Luck Michael

[Landseer]

Won't fit on USA 85 and up, unless you change to the early car bracketing for the alternator and power steering.

Bosch factory rebuild is the way to go. Advance sold my one. Took a few hours for them to get it. Around $150 .

[JK McDonald]

Hey PC085-928S, Landseer is right, Sorry - I may have lead you astray on the option to swap your 928 alternator for a Camero unit. After searching through my files I found several sources for alternator upgrades using Delco parts but they were all for the Pre-85 928 models. I had installed a 130 amp Delco alternator in Miss Purdy (84 model) about a year ago to eliminate a low voltage problem under load.

Perhaps someone can chime in who has found a substitute that will fit the 85 and newer alternator bracket.

Good Luck, Michael

[Normy]

Originally Posted by PC-85-928S

Parked it last night, when I started it later all warning lights stayed on.
Even the central warning light was flashing, indicating low oil level.
I did drive it home, and it seemed ok.
I am feeling it is time to have my alternator rebuilt.
I was looking on line to see the cost of a new rebuild.
Does anyone know the correct Bosh replacement for an 1985 928S US (5.0)
Is it 130 amp or 115A?

It is a 115 amp Bosch alternator. I highly recommend buying one from 928 International, but if you Google "Porsche alternator", you'll find several rebuilt units that are cheaper.

One of the strange vagaries of the Bosch alternator that is mounted on these cars [and many Volkswagens going back to 1977] is that the alternator will not boot-up until the engine reaches about 1800 rpm.

How any manufacturer would allow this to be sold is beyond me, but...it is what it is. I wouldn't have allowed it!

Anyway, my '85 928S2 [the European version of your car; different engine, but same electricals] needs to be revved up before all the lights on the dashboard will go out. This happens every single time I start my car. What's more, in the past, I have owned a '77 VW Rabbit that did the same thing, and an '85 VW Scirocco that also acted this way. These cars happen to use the same Bosch alternator as a later 928. There is a thread on another Porsche website who's name starts with the letter "R" that talks about this phenomenon, and in it, several very knowledgeable people described how to change a certain resistor and prevent this from happening.

If you cant make your dash lights go out by revving the engine above about 1800 rpm...then your alternator is simply dead. About two months ago, I stopped at a marina to get gas with my boat, and when I left...the lights on my dash wouldn't go out. The 25 year old alternator had finally failed. I bought a new one online, installed it my self, and $149 later I was back in business. The hardest part was jacking up the car-

N!

[Landseer]

Normy, you sure that's normal? Check your exciter cicuit. It excites the Bosch 115A alternator well below 1800. I've got 3 of them and none require revving.

PC, 928 Intnl has them, but any Advance can get them. Unless you are local to 928 Intl, why ship the core? Insist on Bosch-rebuild by Bosh (comes in a well-printed Bosch factory box) --- the rebuild is complete including armature. Most other rebuild businesses do a slam / bam and they last short times.

Bosch new is also good, obviously.

Here I had to drive 3 hours in the other car to put a Bosch rebuilt onto the red car. Before it failed, a couple weeks earlier all lights on dash were flashing and battery was low. We tapped it lightly with a rubber hammer while running and got a couple more weeks out of it ( you could hear it engage ). By revving +3000 you could sometimes get it to engage also.

On this trip to VA Beach, the red car had the light flashing occur again, which happened when the battery declined to about 10.5 volts on the gauge. Started flashing when the family was in a traffic jam headed into the Tunnel, which scared them. Right before I lifted the car, tapping again caused it to engage, canceled the flashing dash and cause the engine load to change as evidence.

If you study the electrical training document about the central warning system it suggests that the flashing lights will occur at low voltage, BTW. Obscure reference, but there. I've had it happen to 84 and 86 USA.

Before replacing any alternator, be sure the exciter circuit works.

[PC-85-928S]

a bit confusing
looking on ebay it seems the Bosch AL 170 X is the correct replacement alternator for the 85 928S US 5.0 engine.
some listings say a 115amp is correct, some say 130amp is correct.
One supplier said it is based on production date.
the only number I see on the back of the one I removed is 8001.
i think my production date is 03/85

[Mrmerlin]

you can also buy a used alternator from 928INTL, its half price starts DEC 1st to the 24th

[PC-85-928S]

Bought this one of company on ebay.
Local places could not give me a straight answer on how much to rebuild mine.
Anywhere from $175.00 to $220.00
This was the best price anywhere.
Ordered it on Mon, received on Thursday, no core.
Putting in tomorrow.

Porsche Alternator 928 944 968 1985-1995 AL170X Reman - eBay (item 280557564284 end time Nov-29-10 06:28:09 PST)

[MPDano]

Funny as this is the exact place I bought mine from too. I think mine was an 90amp, then I returned it to them and got a 120amp. I still don't feel like I am getting proper readings as of yet. I even added another ground strap to my engine. It got a little better, but not the numbers others are posting. Still not sure what's going on but I got other things to deal with, so this goes back down the list of things to do.

My Thread:
Remanufatured Alternator Readings - Need Input!

[Landseer]

Its not an item that makes sense to shop for price.
Rebuild shops don't rebuild the whole thing.
Only Bosch does.

Assuming that ebay rebuild is delivering stable voltage right now, going through the charging system is the ticket.
14 pin connector, fuse panel, jump post, the works.

[MPDano]

Originally Posted by Landseer

Its not an item that makes sense to shop for price.
Rebuild shops don't rebuild the whole thing.
Only Bosch does.

Totally agreed on this. I went through a whole big stink with Small Claims Court with a local Alternator rebuilder concerning my wife BMW X5 Alt. I ended up getting one from NAPA, which is a "Remanufactured" Alt and not a "Rebuilt" one.

So far it's been almost a year with zero issues on the X5 and those things are friggin electric hogs with electronic everything.

If I were to do it all over again with my 928 Alt, I would do the Delco conversion and be done with it.