Porsche 928 Battery FAQ
Battery & Brains
In a question dated: 9/15/99
I’ve been reading a couple of recent threads……Let me see if I got this right…
1) The battery on your 928 S4 will go flat if you don’t drive it for about two weeks.
2) If you jump start the car, you will fry the brains of the injection
system.
3) You should swap out the battery instead of jump starting the car. (How this would be different from jump starting the car is beyond me…If you swap out the battery, you subject the system to a 12 volt spike, whereas if you jumpstart, it is probably more like a 1 volt spike, moderated by the electrical capacity of the battery).
4) In either case, you have just reset the brains of the injection system to some sub optimum baseline.
Have I got it right???
In a response dated: 9/15/99
Not exactly. The idle setting need only be reset on 928s that have the Bosch Hammer connections, and apparently, some folks have managed to do it without the Hammer. YMMV.
As far as getting a jump, I would be very leary of it. Replacing the battery with a new one is far less traumatic to the computer circuitry.
However, YMMV.
Merry motoring. Ed
In a response dated: 9/15/99
Yup. It’s like being in a strange place (a VERY strange place) and asking someone for directions. They mumble this and that, point this way and that, shake their head, and finally tell you: “You can’t get there from here”.
Actually……
Due to (previous) three-day battery drain on my car, I’ve jump started it dozens of times, disconnected and removed the battery many times, replaced the battery, etc, and never fried or had to reset anything on my 88 S4.
No matter the rest of the engineering on a 928, can you imagine the bizarro-land type of logic that would dictate that you must have a tech with an expensive testing tool around everytime you change or disconnect the battery? The only way I know of to bring some of the systems back on track after they’ve fone afoul is to DISCONNECT the battery, so that the computer WILL RESET ITSELF and correct the problems.
wk
Dead Battery I
In a question dated: 5/11/2000
I have… or had (!) a Varta 75Ah performance battery. Two years old. It worked perfectly until last monday. There was almost no power at all in the cells. No…i did not leave any power consumers on. Sure. But this is not the issue. 😉 Normally one would find the battery capacity to gradually decrease until useless. But this battery completely died. I’m unable to charge it at all! It takes less than 0.5A when charging, which means… it’s not even charging at all. It is a fairly new Quality battery. My question: what may have caused the battery to fail like this? Anyone? Thanks
Theo
’88 928s4
Response(s)
Theo, I think this is the way new batteries die. I have had three batteries in three different cars in oh, say the last three years, die like this. One day the car was fine, the next, it’s like someone stole the battery. completely flat. Replace it with a new one and all is well.
I do wonder about the two year thing though. Should be some kind of warranty on it, no?
Mark Grasser
1978 928 5-speed
Guards red/black/tan sheepskins
928 OC Charter Member
Yup, still here in Wisconsin, USA.
Man do I wish I had my car back together!!!!!
Response(s)
85 > have an interior light relay 928 618 225 01 located second row next to last relay on the right , it has a time delay 25 seconds plus or minus 5 seconds it also keeps the red door edge warning lights on . They can fail to shut off
Jim Bailey
928 International
jim@928intl.com
79 928 5spd
80 928 5spd
68 911 5spd
Response(s)
My guess is that an internal cell bus bar connection has broken, limiting the amount of current that can flow thru the battery. Be careful! Placing a battery with a broken connector under load (charge or discharge) can result in a battery explosion!
Wally Plumley
928 Specialists
Dead Battery II
In a question dated: 10/31/00
Well, I went to start my car today and, after about 2 weeks of non use, it is completely dead. It has been cold here in the north east but nothing that I was worried about. The car is in my garage and I usually hook up a battery maintainer while it sits there, but of course this time I didn’t. The car has no electrical power at all. I thought that I could just hook up the maintainer for a little while and I should be all set. The problem is that when I hook the maintainer up I usually get a yellow light that comes on indicating that the hook up is complete and the battery is charging. Now, I get no indication at all. The charger wont even kick in because it thinks it doesn’t have a connection. Am I missing something? Why won’t the battery take any charge? I quickly tried to do this before work this morning and I haven’t had a chance to mess with it at all tonight. What should I check next? Any help would be appreciated. I hope
I don’t have to prepare it for winter storage just yet!!!
Rob
87S4, auto
In a response dated: 10/31/00
To be a true “battery maintainer” rather than a “battery charger”, the unit has to have some smarts. One of those smarts is that it doesn’t turn on until it is hooked to a battery. If your battery is totally dead, then the maintainer obviously can’t tell that it is hooked to a battery, so it won’t turn on.
I would suspect that you need to do some basic battery maintenance. I would suggest removing the battery and charging it on a standard charger. Check the electrolyte level if you can. Clean all of the terminals and posts. Clean and wax the battery box. Reinstall the battery and hook up the maintainer.
You appear to have excessive current drain, or a bad battery.
Wally Plumley
928 Specialists
Dead Battery III
In a question dated: 10/29/00
Now I have a mystery that I can’t figure out. There is something that drains the battery after a few days. I measured the current with everything shut off and it is less than 10ma, so there must be something that turns on sometimes or?? Anybody have an idea as to what to look at first?
In a response dated: 10/29/00
My educated SWAG is that the little red lights in the doors are still on because something is indicating that the doors are ajar. In my case it was the rear deck switch that was still making contact even though the rear hatch was closed. I repaired the broken plastic plunger that the ground wire was connected to and that solved the problem. YMMV.
~ Merry motoring ~
In a response dated: 10/31/00
It’s about 10:30 p.m. EST – so I trust those who’ve been out Hob-gobling have returned home. I was doing a bit of trick-or-treating myself earlier today….and it relates to Gary Casey’s question about possible “slow drain-downs on the battery”, and also the “1/2 tooth off” T-belt discussion within the last day or so.
We were doing the T-belt tensioner shuffle on my 84 5-speed acquired in late June (4500 miles in under 4 months….Man – is this a sweet one to drive! Can’t leave it alone….and I commute Zero miles a day to the office!) That and a rear deck that would not electrically release (no key to manual release it either)…plus an annoying “something or other” that was constantly “on” that could drain the battery down if the car wasn’t started every day. (This is where Gary’s inquiry of 10/29 – “mystery battery drain” – or something like that – and Ed Ruiz’s response, which I didn’t see until this evening – comes into play)
When I would “shut the car off” for more than 24 hours – I would have to disconnect the negative battery cable. That would shut off the little red indicator light….located on the pod display in lower right corner – the “bottom” of the amperage guage, which would otherwise stay on until the battery disconnect. The car would re-start immediately with the ground reconnected. Without any time to deal with this annoyance because of a hell of a travel schedule this Fall, I put up with it. Then – 10-12 days ago – I lost my rear deck latch electric-release function. Now I ask you, how convenient do you suppose it is for a 6′ 0 240-ish, late 40’s type of guy to squeeze into the rear half of the car, move out all the assorted cargo items (not including the spare, jack, and elect. pump – which I’d already taken out? Even without need of wrench or vice-grips (I had it arranged for slide on, slide off – with just a proverbial twist of the wrist) it was getting to be damned inconvenient. When the bleedin’ door swung to onto my right foot and ankle while I was stretched out in “disconnect maneuvers” one time – I said that’s &$#*-ing IT!!
SO – Gary…it seems that the round pull-type release switch may not have had a clean contact with the driver’s door light, so the hatch release wouldn’t activate. In other words – it didn’t know the door was open – won’t open if the door is “shut” ; safety design and all that crap. We did a temporary “clean and lube” fix – but will take it up more thoroughly during this winter’s hibernation. What I didn’t realize then – but I think this is what Ed Ruiz is suggesting – is that this door-light, or the door-is-open red indicator light – may also be what is the low and slow – but sure – parasite draining down the battery. A “vicious circle” as it were – in my case. HOWEVER – don’t ask me why that passenger side release would still work for a few days after the other side stopped. Then it ceased as well. My brain hurts too much to ponder that one. (This was the “Trick” part)
…..
John H.
In God and the Whole Tooth
(but not necessarily T-belts) We Trust!
84- 5-spd Fountain of Youth special
Dead Battery IV
In a question dated: 11/2/00
Has anyone replaced the long 12V battery with a shorter (lighter) version? How do you secure this type of battery. I believe Kim Crumb has made some type of mod to fit the smaller battery.
My battery goes dead afetr 10 – 14 days if the shark sits idle. Something in the car is draining the battery (it is not the battery since I have tried many). Do the automatic cut-off switches (like the one from Groit) work?
Gary
In a response dated: 11/2/00
Gary –
I don’t know about “automatic” cut-off switches. But this battery drain thing is so common a lot of owners and “wrenches” recommend a simple mechanical “battery disconnect switch” for extended non-use. Interrupts the negative battery terminal connection. It can be located in the rear deck area (so you do not have to empty and open up the spare tire well every time you want to disconnect the negative/ground cable ) or you can wire the switch to a point “up-front” – if you are going to concede the fact that you probably won’t be fixing the real cause of the drain-down in the near future.
As for some possible causes of the “slow drain down”….go back to the List entries in the last 2 days – look for input from Ed Ruiz and my own “drain down” discovery – in response to Gary Casey’s similar inquiry. Heading is “mystery” or “mysterious”.
John H.
“Was drained, but now am free”
(Sung to the tune of “Amazing Grace”)
In a response dated: 11/2/00
I installed a battery switch in my gt. I used one of the simple 2-pole on/off track type switches from automotion. I made a right angle bracket about 2″ on each leg, mounted it on the battery ground mount, behind the tool kit cover, then mounted the switch with one terminal right onto this bracket. Then the ground strap goes to the other switch terminal. I cut a small slot in the tool cover so that you could remove that without removing the switch key. Very handy when working on the electrics or leaving the car for a couple of weeks or longer. Mount a wire lanyard out through the drivers side of the rear hatch if you race the car, remove that lanyard when you are not on the track. Works good, very handy.
Don Hanson
Dead Battery V
In a question dated: 5/22/99
After marvelling at my nice clean carpets, I decided I was done for the night and tried to roll the windows up. Nothing happened. I glanced at the clock and radio – no lights. ^*&$^! Dead battery again. I had my doors open for several hours today, but flipped the switches on both of the door lights so that they wouldn’t turn on. The other cabin lights need new bulbs, so I haven’t bothered to see what position they are set in. Do the lights in the trunk come on when the doors are open? (I didn’t set those off) The car has been sitting for about 6 days anyway (seat renovation), but it had power this morning (enough to get the windows down:). I wouldn’t think the regular clock and the clock on the radio (aftermarket) would be enough to drain my 2 year old battery, so what else could be doing it?
Thanks,
Mike Briggs
86 928S
In a response dated: 5/22/99
You forgot about the red marker lights on the door. They are both on when either door is open. And furthermore, they stay ON using the same time delay relay as the interior lights. So every time you open a door…both lights come on, and stay on even if you close the door immediately. So if you are opneing and closing the doors often, the red lights could be on for a very long period of time. IMHO, this is a pretty stupid design…can cause a lot of unnecessary grief.
Steve – 87S4/auto/GPW
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Section 2: Battery Recommendations
In a question dated 3/23/00:
Hello All,
My 87 will soon be needing a new battery, and I want to get the best battery that will fit. So, do any of you have any recommendations?
Thanks,
Randy Page
87 S4 Auto Black/Black
In a response dated: 3/23/00
Interstate MTP91
About 90 bucks plus tax.
Wk
In a response dated: 3/24/00
An authentic Porsche battery. Let your car know you care enough to give it OEM!!! $125 plus tax (from the dealer)
— Andrew
85S 5-spd
In a response dated: 3/24/00
Be sure to put Porsche electricity in the battery — I prefer the interstate battery — more distributors for warranty – A much higher volume of sales — potentially shorter storage on the shelf – I have had Porsche batteries fail in less than one year –
Jim Bailey
928 International
79 928 5spd
80 928 5spd
68 911 5spd
Recommendations II
In a question dated: 5/21/1999
I need a new battery for the shark. Any opinions/suggestions on a good aftermarket battery (brand/model #). What are you guys using?
TIA
Dana ’85 928S
928 Owners Club
In a response dated: 5/1/1999
“Interstate MTP-91.”
Merry motoring, Ed.
Response(s)
In a message dated: 5/1/1999
I can tell you what NOT to use…the Optima that is supposed to fit the 928 is too tall and the posts will touch the top of your battery box cover.
We use Sears, Exide, Porsche (Douglas), all with about equal success.
Susan Kirby
DEVEK
In a response dated: 5/1/1999
I use Porsche Batteries personally, but you can get as good or maybe even better one at Sears or NTB. It is the Sears Diehard Part # 22836249, retail is $106.99 , but mention a trade discount and you can get it for around $89. Fits all 78-86(early) 928s.
David Roberts
928 SPECIALISTS
In a response dated: 5/21/1999
Dana,
My 86 came with a Interstate battery. I replaced that battery this Spring with a Auto Zone brand (1/2 the cost, $60)and it works great. I am unsure of the group size but, any battery dealer can tell what size you need… only one group size fits properly.
-Pete
86′ 928s
Recommendations III
In a message dated: 10/13/00
A while back, I proclaimed my great satisfaction with a Champion battery I bought at Sam’s Club for my ’85 928 for less than half the cost of Interstate/Excide/Porsche etc. batteries. Well, that was January, 1998 and my Champion battery is now kaput. So it didn’t quite make it 3 yrs. Not very good, though it was an excellent performer while it lasted.
I’m now testing a Dura-Last from Auto-Zone ($60). I has a 2 yr free replacement warranty and a 7 yr prorated warranty. Something tells me I’ll be collecting a partial refund at the end of this one’s life. I’ll report on it’s demise when it happens.
Ed Croasdale
’85 5-spd
In a response dated: 10/13/00
Ed,
Your experience is the same that I have had with Champion batteries. GNB (Gould National Battery) makes the Champion along with a host of others , you can usually find “GNB” on the label or molded into the plastic. If I find those letters I won’t buy it.
-mark
In a response dated: 10/13/00
As mentioned at the last Frenzy, the consensus was that maintenence -free batteries are not very reliable. I use Interstate (non-maintenence free) batteries in all my cars and have only had one go bad. (It was replaced at no charge.) They tend to last 5+ years and (so long as the fluid levels are kept above the plates) provide consistent voltage and enough CCAs to start the car, even on very cold (sub 15 degree F.) days.
My advice is to pay the extra few bucks for an Interstate battery and save yourself the potential aggrevation you may get from a maintenence-free battery. YMMV.
~ Merry motoring ~
Ed Ruiz
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SECTION 3: Battery and Memory
In a question dated: 7/9/00
Is there any way you can unhook the battery/power yet still keep power to the “brains”. Im heading to Hotlanta for training today and will either have the car parked at the airport or at home here for an extended time. I just don’t want the hassle of unhooking the battery terminals..hooking them up all the time then having the car run rough for a while as the brains remap everything. I would like to take all the items i can “off line” except the brains memory as to preserve the battery over an extend storage time? can it be done..and if so..could a switch be wired in so it could be done from the inside?
Thanks
Tony
In a response dated: 7/9/00
Tony,
I’ve seen a gizmo that uses a 9 volt battery hooked up to the cigarette lighter to maintain the computer settings. Don’t know if you have to connect the battery posts together for it to work. Believe I saw it at JC Whitneys.
Dennis
Response(s)
Spend a little extra money and buy a Schumacher battery tender for $30. Anything else is junk compared to these things. Get them at Wal-Mart or from Schumacher direct. The link is on my web pages links page.
Brian
Brian E. Buxton
Battery Charger
In a question dated: 2/3/99
Could anyone suggest good battery chargeres for my shark sitting in the garage?
Thanks in advance,
Chihiro
chihiro hosoe
chihiro@dynamicdiagrams.com
86.5 928S 5psd meteor metallic
In a response dated: 2/3/99
one of those automatic trickle/shut off kind? really I think the key is to disconnect the ground cable during
extended storage. You loose your radio presets and maybe error codes
in FI brain but no big deal, better than getting in ready to go and
cliiiickkkkk!
Phil
In a response dated: 2/4/99
Chihiro:
Wal-Mart sells a “battery buddy” trickle charger (1.5 amps I beleieve)
that automatically shuts off when it senses a full load. It was designed to be mounted in the engine compartment, however, most people I know will mount it on the wall in their garage next to an electrical receptacle. Then fabricate a “quick connect” system to the battery terminals with hardware from the local Radio Shack.
Regards,
Joe Rausa ’89S4 (fully loaded battery)
In a response dated: 2/4/99
I’d recommend the Schumacher SE-5212A. It’s fully automatic so you can’t overcharge and has 50/10/2amp output for starting, fast charging, and trickle charging. I bought mine at Wal-Mart for ~$50, or you can buy them online at Schumacher’s web site.
http://www.batterychargers.com:80/top.htm and follow the link for Metal_Hand-Held_Portable_Chargers.
I’ve used this on my ’83 for a couple of years with great results. Does anyone out there use something similar on their S4? The S4 owner’s manual makes me leary of trying any kind of charging on that car for fear of frying the brains… Any insight would be appreciated.
—
Jim Stadter
’83 928 S 5-speed (U.S. spec)
’88 928 S4 5-speed
Hill Country Region PCA (Austin)
928 Owners Club (http://www.928s4vr.com/928OC.html)
In a response dated: 2/5/99
Chihiro:
The best solution I’ve found for my little boat batteries is a 1.5amp automatic maintainer made by Schumacher. If you have a Performance Products catalog you can see a picture of it. About the size of a couple hockey pucks, it’s intended to be mounted on the side of the battery, and comes with a pair of eyelet-terminated wires to connect it to the battery. A little 8″ pigtail requires an extension cord for power.
The charger is automatic, and turns itself on and off as required to maintain the battery between 13 and 14 volts. The relatively low charging current means there’s little chance of boiling the electrolyte out of the battery, but you should check it periodically just the same.
Now the great part: Wal-Mart sells ’em for about $25. Look for them on the attery and charger display, hanging up in a plastic display package. This is the simple/cheap/easy/effective solution for off-season maintenance. If you are in an area where it’s cold, the heat from the charger will warm your battery’s little heart, too.
I use mine to keep a few Sea-Doo batteries happy. They live on an oversize trailer, and get towed by one of those SUV things that Gene seems to hate. 🙂 That’s me over in the right lane, Gene!
dr bob
Battery and Electronics
In a message dated: 9/13/199
Dear fellow sharksters:
If the battery is disconnected, then the Bosch Hammer is required to reprogram the computer on GT’s and GTS’s. For all I know, it may be required for all S4 models too.
In a message dated: 9/13/00
Response(s)
Ed, if your GT still has it’s owner’s manual go take a look at it – or take a closer look. I will dig my owner’s manual out tonight and double check but I’m almost certain that mine clearly states that the system will re-adapt after 10 minutes of driving once the battery is disconnected.
I do not believe that there is any truth to the legend that the Bosch Hammer has to be used to “reprogram” anything after the battery is disconnected and reconnected. (My experience is consistent with my opinion on this subject.)
However, I would be very interested in any specific non-anecdotal evidence you have to the contrary; We might have conflicting technical documentation.
— David Chamberland
91 928GT
928 Owners Club Charter Member
Response(s)
In a message dated: 9/14/00
Dear Daves:
I just checked the Service manual, and called a 928 tech to verify. If your 928 has the Bosch Hammer connector (next to the passenger seat), whenever the battery is disconnected the Electronic Idle Control in the LH computer may need to be re-adapted. In most cases, the computer will go to a base setting, which will work fine for most driving conditions. In some cases, the computer will store the original settings for a short period. However, it will not adapt on its own or learn your style of driving. To be
certain, having it re-adapted with the Bosch Hammer is prefered. YMMV.
Merry motoring. Ed
Battery and Electronics Cont’d
In a message dated: 9/14/99
As promised earlier today, I dug out my owner’s manual. On page 95 it states:
“If the battery is disconnected, the data for the engine electronics stored in the control unit are erased. When the battery is reconnected, the engine should be run for approx. 10 minutes to allow the control unit to re-acquire these data. During this period, the engine may idle unevenly or too fast.”
As owner’s manuals tend to emphasize “service by an {insert automaker}authorized service center” whenever and wherever possible the above paragraph leads me to believe that there is no requirement for additional twiddling with the electronics after the battery is reconnected.
Later in the day, Dave Roberts pointed me in the following direction:
“From: “928 SPECIALISTS” Date: Tue, 14 Sep 1999 12:25:41 -0400″
I think Ed is possibly speaking of the “System Adaptation” (calibration) concerning the Electronic Idle Control in the LH computer, see Vol 1, section 03, page 15 of the Workshop Manuals.
On the above referenced page appear instructions for carrying out “System Adaptation” with the Bosch Hammer:
“System adaptation can be carried out with the tester. That is to say that the electronic idle control in the LH control unit is adapted to the actual air throughput and to the current condition of the engine.”
Instructions for initiating “System Adaptation” with the tester are presented. The section ends with:
“The engine must now idle for at least 30 seconds.”
“System Adaptation is then terminated.”
“Ignition Off.”
On Page 01 of Section 3 in volume 1:
“Important: Do not disconnect the battery or the connector of the DME control unit before diagnosis as otherwise the error memory will be erased.”
Lastly, to my knowledge Charles Probst’s “Bosch Fuel Injection & Engine Management” (a good book even though it appears to have a few errors) makes no mention of special procedures with respect to Bosch pulsed fuel injection systems with electronic idle stabilization after disconnection and reconnection of the power source.
The evidence so far uncovered leads me to believe that the Bosch Hammer can be used to initiate and complete in 30 seconds the process of System Adaptation after battery reconnection. However, even without the Bosch Hammer the system will adapt in 10 minutes.
I can think of several reasons why a shop would want to be able to quickly adapt the system after a battery disconnect. One in particular would be forestalling an owner, otherwise unaware of the 10 minute adaptation period, from complaining to the shop of an irregular idle after service. Another reason might be to cause the system to re-store error codes during diagnosis or repair of a fault.
Based upon the evidence so far available, I’m still convinced that use of the Bosch Hammer is not necessary after reconnecting the battery. But, let’s not take my word for it! If the truth is out there let’s find it.
— David Chamberland
91 928GT (Amazonagrunmetallic: Green. NO! Blue! Ahhhhhhhhhhh!)
928 Owners Club Charter Member
Changing Battery Tips
In a message dated: 6/12/99
When changing your battery, it is preferable if you can keep 12V supplied to the car so that electronic brain settings and radio memories are maintained. Here are two ways of doing this.
The first requires two sets of jump leads (they don’t need to be capable of carrying much current – 1amp capability is fine):
1a) Use a set of jump leads to connect new battery positive terminal to the auxiliary start post under the bonnet (hood) and new battery negative terminal to bolt head on engine bay cross-bar.
1b) Remove old battery (disconnect Ground lead first, then positive lead).
1c) Use second set of jump leads to connect old battery to auxiliary start post under the bonnet and to bolt head on engine bay cross-bar.
1d) Disconnect new battery from auxiliary start post and bolt head on engine bay cross-bar.
1e) Install new battery (connect positive lead first, then Ground lead).
The second way is simpler but requires an additional battery (an old one will do, so long as it can supply a little current at 12v):
2a) Use a set of jump leads to connect additional battery positive terminal to the auxiliary start post under the bonnet (hood) and additional battery negative terminal to bolt head on the engine bay cross-bar.
2b) Remove old battery (disconnect Ground lead first, then positive lead).
2c) Install new battery (connect positive lead first, then Ground lead).
After installation of new battery, ensure that the battery hold-down strap is correctly fitted. Also ensure that a terminal cover or piece of insulating material is fitted over the battery positive terminal to prevent shorting to the battery compartment lid.
Check the condition of the bolt or wingnut at the point where the battery ground lead is attached to the car and if it shows signs of rust clean it up and apply battery terminal protector (usually supplied in aerosol cans).
You can now be confident that your battery is safe and secure and that your 928 will have been unaffected by the battery change. —
Jonathan M Rackowe
JMR Technical Services
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Changing Battery – Precautions
In a question dated: 7/3/00
I want to change the battery of my 93 GTS. The task seems to be fairly simple but…with so many electronics on board I am afraid of messing up anything. Any precaution to take before disconnecting the battery (apart from having the engine off of course)?
Regards
Juan
1993 GTS 5spd
In a response dated: 7/3/00:
1) If your radio needs a code to operate, be sure that you have it.
2) Always disconnect the ground (earth) connection first, and connect it last.
3) Be careful in lifting the battery out – they are heavy and the box is quite a stretch. You can strain your back, spill acid on the carpet, or drag it on the carpet. You might consider protecting the carpet, and possibly climbing inside to get the battery out of the box.
4) Clean all of the connections inside the battery box. Earlier cars have the speedometer/odometer connections inside – yours doesn’t, since the speedo drive is off of the left front ABS sensor.
5) It will take a few minutes for your computer to reprogram itself afterward. You will lsoe all of your radio station settings, etc.
Wally Plumley
928 Specialists
Battery Sizes
In a question dated: 1/XX/99
The 928 uses a “group 49” battery, I believe. Or maybe its a “group 48”? The difference is which end has what terminal. Only this battery size will fit right.
In a response dated: 1/XX/99
Yes and no, the 78-early 86 uses a group 49 (the long battery) and the 86.5-95 uses a group 48 (standard size battery) . The change from the long (49) to the shorter (48) was due to the re-routing of the dual exhaust in between the differential and the battery box on the 86.5 and newer 928s.
David Roberts
928 Specialists
Battery Burns
In a message dated 5/22/99
Listen to what Marc says, he know for what he speaketh.
When I picked up my blk 88, the PO was kind enough to put in a new battery. Two days later while traveling through a massive road construction site, the car up and died. With no where to pull off and the flag lady going bersek, the car started to fill w/ smoke from the rear. Seems as though the positive cable shorted out on the lid. Car did restart on first crank, luckily as there were a lot of pissed off (hey Gene, can I say that) people stuck behind me.
Doc
whose blk interior is now slightly stained brown 🙂
p.s. go to Wal-mart, code # 42-4 me thinks. Really inexpensive, major brand
made, direct replacement and exc waranty.
Response(s)
In a message dated: 5/23/1999
I’ll second that. I have two characteristic “burn” spots on my battery compartment lid that indicate one of the PO’s had a similar “exciting” incident. The advice about choosing the correct battery is warranted.
Dave Kelly
88 S4 Indischrot/Tan
928 Owners Club
PCA – Connecticut Valley Region
In a response dated: 5/23/1999
FYI, if you look on the Porsche battery and most of the other good batteries you will notice 2 small holes on the outside edge of the recessed area near the positive terminal. These are receptacles for the hinged “Positive Pole Cover” that came on your 928 originally and is still available from Porsche. It will keep the positive connector from hitting the battery compartment lid even if you don ‘t have it properly secured with the battery hold down bracket.
Part # is 999.611.104.00, Porsche’s retail is $2.65, but it can be bought for less at certain places .
David Roberts
928 SPECIALISTS
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Voltmeter
In a question dated: 3/29/2000
Jason D Wheeler wrote:
Is this the beginning of the end for my alternator? Or is it something much simpler (read: less expensive)?
A couple of days ago, the voltmeter guage on the dashboard starting going haywire. It would be fine for a while giving off a reading of just under 14 most of the time, but then suddenly would jump through the red zone to the top of the guage (16) and beyond(!?) for a matter of seconds before settling back to it’s normal reading. I thought at first that perhaps the guage itself went on the fritz (as they are known to do); however, these increased readings were actually accurate judging from the intense brightening of the headlights and the higher pitch whine of the fuel pump and/or cooling fan (if any of them happened to be audible at the time). So my guess is that something in the electrical system is no longer doing its job of ensuring that only the right amount of charge flows to the various systems and back to the battery. Forgive me if my knowledge of electricals (like most things mechanical) is elementary at best.
Could this be a problem caused by the impending failure of my alternator, or is there a regulator in the system somewhere that is no longer monitoring the charge shooting through the components?
It’s nice having supercharged components, but I’m afraid at this voltage, many components are doomed for failure, or even worse, could I be sitting on a timebomb (potential battery explosion)? Fortunately, the surge in electricity only last a few seconds at a time, but I noticed it getting longer in duration
Good job of observation and reporting, and a good guess on the problem.
In a response dated: 3/29/2000
The alternator sounds fine. Yes, there is a voltage regulator mounted on the alternator. Either that regulator is failing, or it is not accurately measuring battery voltage due to a wiring problem. The regulator/alternator uses the battery as a reference voltage and voltage stabilizer, and having the battery come disconnected while the alternator is charging the system can cause serious voltage spikes that can damage almost any of the electrical components on the vehicle. Murphy’s Law assures that the damage components will be either the most expensive (such as a computer) or most difficult to replace (such as a major wire harness).
A brief spike won’t hurt the battery, and long term slight over-charging is more likely to damage the battery than brief high voltage.
The suggestions that you have received thus far about accurately checking the system voltage are right on the money, but I’m afraid that the bright light and fast fans tell the tale. The voltage regulator is the easiest answer, but if a new regulator doesn’t solve the problem, you may be in for a frustrating gremlin hunt.
As a simple first step that may or may not solve the problem, but should be done periodically anyway, open the battery box, remove the ground strap (which on your ’84 should be held by the infamous wingnut!), then remove and carefully clean the battery posts and terminals and the chassis ground cable and connection point.. Disconnect the chassis ground first, then the battery ground cable, then the positive cable. Replace in the opposite sequence, ending with the chassis ground. If you are luckier than you can expect, that will solve the problem, but don’t count on it.
You can buy an alternator from us or any of the other suppliers, or you can have the alternator rebuilt, including a new regulator, brushes and bearings, locally at any good automotive electrical shop. Be sure that the alternator cooling cowl and hose get reinstalled.
Wally Plumley
928 Specialists
Corrosion at Jump Terminal
In a message dated: 8/3/99
Marc White shared his story of wire corrosion at the underhood jump-start terminal – everyone should be aware that there should be a plastic cover over this terminal connection block, as well as a plastic cap covering the jump terminal itself. If you can see the wires connecting to the terminal, your cover is missing!
If this cover is missing, water runs from the hood seam directly into the terminal and wires. If your cover or cap is missing, get on the phone to Dave or one of the other vendors ASAP!
Wally Plumley
928 Specialists
White Powder
In a question dated: 11/10/00
Big surprise, my Walmart battery died today after 3 years(that’s good for WM batteries). Decided it was time to get a quality battery. I remembered reading good things about Interstate here on the list. Found a dealer and the Interstate book called for a MTP-93 for an 86 928. It was way to long but I found that the MTP-91 fit well.
Anyway, there’s lots of white powder and flaking paint inside my battery box as well as some rusted through metal (not much). I figure I’ll clean it with a wire brush. Does anyone know of a way to keep the powder from coming back? I was thinking maybe a thin coat of electrolitic? grease.
Don Carter
In a response dated: 11/10/00
The powder is corrosive residue from your dirty and discharging battery (bad boy). Mix up a batch of baking soda and water to remove and neutralize the gook, then paint the box with bituminous paint. A battery mat is not a
bad idea either.
Marty