Alternator / Battery problems

[StuK]

Hi all

About a month ago I thought I was going to have to replace my battery - I’d been away for a long weekend, which involved around 7 or so hours of driving. When I got back home the car wouldn’t start as the battery was dead. I assumed that as the battery was a few years old now, it needed replacing and that I hadn’t noticed until now because I always have it plugged in to a battery conditioner. So, once I had enough charge in the battery I took it to my local garage to get a new battery. They tested the battery and said that it was fine, but the alternator wasn’t delivering any charge. I briefly looked at what would be involved in replacing the alternator and decided it was in the ‘top difficult to deal with now’ category and I’d get it sorted when I have the annual service done at the beginning of December; I don’t use it much during the autumn/winter so I couldn’t see this being a problem.

Then, a couple of weeks ago I saw that the Goodwood Breakfast Club were having an 80s theme and I really fancied going to that. So, early on Sunday morning I headed off on the 2 hour drive to Goodwood, with some trepidation and an unnatural focus on my voltage needle! I said to myself if it dropped below 12 I’d turn round and head back home (as long as I wasn’t over half way there). Within 10 minutes the needle had moved from around 13 to just above the 12v marker, but then it stayed there, even though I had my lights on. I continued on my journey and as soon as I felt it was light enough to turn the headlights off I did so, despite some other drivers thinking it wasn’t light enough, but they didn’t know the emotional trauma I was suffering! For the rest of the drive down the needle hovered just above 12v, sometimes creeping up a bit, sometimes creeping down a bit, but it never dipped below 12v.


Well I made it to Goodwood, had a nose around the bounty of 80s cars on show and then started worrying about whether there was still enough juice in the battery to turn the starter motor. I needn’t have worried, it started fine, the needle was somewhere between 12v and 13v so I decided it would get me home (2 1/2 hour drive).

I did continue to suffer from voltage anxiety all the way home and had one particularly hairy moment when the needle had dropped below the 12v line and I encountered stationary traffic on the M25. I was worried that the cooling fan would kick in and suck the remaining life out of my battery, so as a precaution I turned the heaters up and sweated even more for a few minutes until the queues dissipated and I continued on my way.

In the end I got home without incident and tucked the car away in the garage and plugged the battery conditioner back in.

So now, a puzzle. I assume that the alternator isn’t completely fried, as presumably if it was I wouldn’t have got all the way to Goodwood and back. I also assume that the alternator must be working at least partially as there were times that the voltage crept back up on my journey.

Does anyone have any idea about what might be going on here and how it could be remedied?

Thanks

Stuart

 

[scam75]

You'll need to put a multi meter across the battery with the engine running to see what's happening. The dash gauge cannot be relied upon after 30 odd years. I would agree you must be getting some charging. A reasonably healthy alternator should put out about 14v with engine running and nothing else switched on. It will drop a bit with more electrics getting used.

You may have a failing alternator, heavy resistance across the main power cables, or a slack or defective belt, or all 3! Also check your alternator cooling duct is present and correct. A cooler alternator is a better alternator.

Good luck

Stuart

 

[vincematthews]

I'm afraid I can't remember who I borrowed the checklist below from, but it came in useful when I had similar faults. Additionally, any of the main cables to & from the alternator, the starter and battery are worth checking along their length because they run past the exhaust (good design?). Depending on which alternator you have the voltage regulator is usually a bolt on part which you should be able to get separately (from an auto electrician?) for not much money.

"How To: Checking Alternator Faults

In response to many posts about alternator problems, I've written this guide to help with finding out where your problem lies.

You will need a multimeter or voltmeter able to read 0-20v

First thing, check these fuses.
AM2 (7.5A)
Charge (5A)
Engine (10A)
All in the engine bay fusebox

Now carry out the following checks with a good, fully charged battery fitted:-

* 1. Measure the battery voltage with the engine and ignition off, should be over 12v (more like 13v) take a note of the voltage for reference
* 2. Start the engine and check the voltage across the battery again, should have risen to over 13.5v.
* 3. With the meter still on the battery increase the rpm to 2000, voltage should be at least 14v.

If it fails any of these checks, then you either have a faulty alternator or wiring. (assuming you paid attention and have a good, fully charged battery)

Next carry out these checks:-

* 4. Take the plug out of the alternator, switch the ignition on, (engine not running)
* 5. Use the meter to check from each of the 3 pins of the PLUG to a good earth, you should get around the battery voltage (that you noted in step 1) on each pin
* 6. Use the meter to check from the large bolted terminal on the alternator to a good earth, you should get around the battery voltage (that you noted in step 1)

If you don't get battery voltage at any of these 4 points, you have a fault on the wiring.

If you do get the battery voltage at each of those 4 places then the alternator is faulty.

If you have a wiring fault it will be on the wiring from the points where you don't get battery voltage, use the meter to track back the wiring and find the fault."

 

[Waylander]

Probably just needs a new voltage regulator, same as a Granada,

About £6 from wood auto, or £97 from Porsche, which is a Bosch Part
1 197 311 040

And its possible to change it without removing the alternator, be easier if you have 4 foot arms and tiny hands, only held in with 2 little set screws

 

[bmnelsc]

I went thru similar troubles with my '91 S2 with alternator output (cold) at 13.6V (the regulator limits output to this number) with it dropping off as things warmed up until eventually it would barely charge at all. After much testing it was found that the main battery cable was the culprit. The clamps were perfect and what little exposed wire was there looked clean also BUT once skinned a little, there was corrosion in the cable (surrounding the strands) which dropped voltage capacity as the corrosion caused the cable to heat up. Cable is only available as a "set" from Porsche and not cheap (over CDN$300) but with a new cable no problems and the car turns over faster on startup as well.

This was hard to find - as using probes, etc the cable looked ok - it was only under an operating load that it would heat up and create a lot of resistance. The regulator and then the alternator were replaced to NO BENEFIT before it came down to the cable (last potential obstacle). I would say its worth bench testing the alternator before committing to a part replacement as I believe the original components are good for A LOT of miles. A rebuilt alternator is half the price of a cable so replacing an alternator unnecessarily makes this an expensive repair.

 

[Waylander]

Hi Bruce

this seems to be a LHD problem and not restricted to 944, I was reading a piece on the USA 968 forum about a main battery cable on a 968 breaking down and causing the starter motor to kick in, unfortunately for the owner the car was in reverse and drove itself through the garage door which was closed and half way down the drive before the cable failed, apparently this is not the first incident that has been reported.

i have searched but cannot find any reference to this happening in Europe with LHD

So I think replacing the main power cable is a good idea anyway, just it’s NLA for RHD cars