Strange Alternator Problem

My car has done a strange thing on 2 occasions this week. I committed the cardinal sin of washing the car on Friday but didn't take it out for a spin after to dry out the brakes. The first time I used it was Monday and when driving off, I thought the wipers were quite slow. No warning lights were on but the voltmeter indicated only 11.5V. There was no difference even when I revved the engine. I decided to turn back to swap cars and just then the voltage then moved up to 14V as per usual and everything was back to normal. I used the car the whole day and there was no further problems. Voltage remained rock steady throughout the day and yesterday. I didn't use the car today until this evening. It had been sitting the whole day outside and it has been raining the entire day. When I started the car this evening, the same problem occurred again. It lasted about 2 minutes like on Monday. The voltage sat at 11.5V with no difference when I revved the engine. I sat in the car with the engine running at idle to see what happens. Basically the voltage flickers between 11.5 and 12V and then after about 2 minutes, it climbed to 14V and all was back to normal again. I wanted to see if this has ever happened to anyone else especially after washing the car or leaving it outside in the rain. I haven't had time to plug it into the diagnostics to see if any faults are logged. I suspect low voltage will show up in some modules. I wonder if the alternator was soaked by me washing the car that caused the problem.

I don't think that it will have much to do with rain or washing. It could be that either the alternator or the regulator on the alternator is on the way out (How old is it? How many miles has it done?). Mine gave out at a frankly unbelievable 10k miles! I would get your local auto-electrics guys to put a test on it while she's running - see if there's any big fluctuations in the output. Should be around 13.7 volts & steady. Avoid any long journeys until you've sussed it out too. I had a very embarrassing experience on a petrol forecourt after paying for my fuel and returning to the car; alarms, raising rear spoilers and general carnage! Plus I couldn't get back in to my own car. Oh, how they all laughed! I'm still in therapy for that one!! My £250 diesel Citroen has done 186,000 miles and is still on the original alternator...... That's torn it! [ ]

My car is an '04 car with 35k miles. I did suspect that the alternator or more likely the regulator may be faulty. I will test the alternator tomorrow - I have kit to test it http://www.tractioncharger.com/battery-tester-model-500.php

Nice one! Let her run for a while, you might find that she's giving you 13.7 for a while but then drops off to 11, etc... Best of luck anyway!

If you need to change the regulator/diode pack, check out this DIY: http://forums.pelicanparts.com/porsche-996-997-forum/408495-alternator-repair-regulator-replacement.html

Funny thing is that hasn't happened yet. It did with the Carrera and a new regulator sorted it. In this case it's 11v for a short while then up to 14v as per usual and settling at the usual 13.5v after a few miles and rock steady. Thank you Richard for the link. Here's another http://www.dakingrulez.com/porsche_996_turbo_Gt2/diy/remove_alternator/porsche_996_turbo_gt2_remove_alternator.shtm

Alternator tested fine. Battery is good. Indy thinks it may be the power cable behind the alternator that may be the problem.

Seems odd as you car is quite young & has low mileage too....[8|] At least it doesn't look like you've got to find £250 for a new alternator! [ ]

The power cable problem seems to be quite common in older cars. Mine is 8 now. £250 for alternator is acceptable if you consider that the engine may have to be dropped to change a £90 cable! Oh the joys of having the engine stuck in the rear. The Indy will try to do it without dropping the engine first.

This is interesting because my car does exactly the same thing. It's always after it has rained heavily and the car is wet. When I start it up the voltage is very low and the power steering is not working. After a minute at the most the voltage goes back up to 14 and power steering is returned. It's accompanied by what sounds like a belt slipping. So far it's always righted itself but I had made a mental note to get my OPC to check it when it goes in for it's next service.

That sounds like your ancillary belt is too loose & it's slipping when it's wet. You're then hearing the belt 'biting' on the drive for the alternator - & possibly your power steering unit - when the belt drys. I might be wrong on this one but I think that there might be some sort of mechanism that brings the belt tensioner in a few seconds after you start the engine (?). I only say this as I also get a distinct short screeching sound like a belt biting when I first start the car after she's been washed - but it's very short & there's no loss of voltage, let alone power steering loss.

The tensioner is completely mechanical and applies a constant tension. A slight squeal at start up after washing the car or being in the rain is quite normal. It is as Adrian966 describes. However my car is doing exactly as AndrewEllinas' car. It only happens when it has rained or the car has been washed and lasts 2 minutes at the most. It makes no difference whether you blip the throttle or not (as in old cars with faulty regulators and you have to rev it past 2000 rpm to excite the alternator). When it is not charging I've had a look in the tne bay and the belt is not slipping. It does look like its the alternator or as the indy says, the power cable. It will be interesting to see what the OPC says when AndrewEllinas leaves his car in. Keep us posted. Min

Removed the alternator earlier in the week and got it refurbished. The spark I use replaced the regulator, bearings and machined the slip rings for £90. Put it back in tonight and all seems ok now. Will see how it goes over the next few weeks. Will post a DIY later on how to remove the alternator.

An update on the refurbished alternator - it is working a treat. HOWEVER, after changing the power steering pump 2 nights ago and cleaning the engine bay of Pentosin the alternator got wet and guess what happened, the car started with 10V showing until a minute later then it kicked in with a squeal of the drive belt and 14V showing. I changed the power steering pump as I have been experiencing a dry bearing noise from the power steering pump when warm over the last 2 months and was afraid of the bearing letting go. The idler pulleys were replaced earlier in the year and the alternator bearing was new from the rebuild. The noise was present even before the alternator was playing up. I got the pump from America and even after paying vat it only cost me £320 for a new Porsche one rather than £500 for a new or £346 for a rebuilt one from OPC. After I spent 4 hours changing the pump, I started the car safe in the knowledge that on the balance of probabilities, the noise should now be absent. Imagine my disappointment when there was a constant squeak (like an unoiled bike) and again it seemed to be coming from near the new pump. And with the voltmeter showing 10V, it really was a kick in the sensitive region. Given the problem only occured when wet I decided to replace the drive belt as it was only £18 from mister-auto.co.uk (with discount code MA35) for a Continental Contitech one. It was not something I had planned to change as I only replaced it 11 months ago with an original Porsche one when I replaced the water pump. Would you believe the car is now completely quiet and my alternator problem is history. Moral of this long and and probably quite boring story is that if you have a squeal coming from the engine bay and your alternator is behaving as above, then even if your belt was replced in the last year, try changing it first as it is quite cheap and easy to do. While you are at it give all the pulleys a clean with brake cleaner. If your voltage starts at 14V then drops as the car warms up then the alternator regulator is probably faulty. When changing the belt, you will have an opportunity to give the idler pulleys and all other rotating pulleys a twirl to see if any are running rough or have play in them. Hope this helps someone.

Incredibly well timed post Minny, my voltage dropped this afternoon, all was well and running at just below 14v then started to drop slowly.I wasn't too far from home so managed to return before it died, I assumed it's the alternator so was considering second hand or recon,is there anything else I should check before diving in at the deep end?

If it starts at 14v then drops as the car warms up it is likey to be a dud regulator. If you are handy with spanners, remove the alternator yourself and replace the regulator yourself. I can guide through it and the part numbers for the regulator. A couple of Bosch ones are interchangeable. The regulator is only £30-40 and 2 hours of your own time. Nothing complicated or tricky just a bit to remove to get to the alternator. The regulator takes 5 minutes to change. I got mine refurbished with new bearings and re-machined slip rings for £90 including a new Bosch regulator.

Hi Minny,thanks for the reply,I suspect mine is the alternator as the voltage starts to drop straight away from start up.I'll start to strip it this weekend,there's no special tools required is there? I'll let you know how I get on and if there's any problems you've just become my new best mate, thanks mate, Gaz.

No problem. No special tools required at all. If you wait a day or 2 I've just done the write up and sent it to Richard Hamilton who will put it up in the Technical section over the next few days. Its for a turbo but the cars are both similar and if your are stuck PM me and I can look up my Bentley Publishers manual for the Carrera.

Thanks,you're a gent.

Here it is: http://www.porscheclubgbforum.com/tm.asp?m=735206 Gary, you won't be able to access that section of the forum, so drop me an email and I'll email you a copy if you want it.

My car goes into my OPC in January for it's MoT and a small service. I'll tell them to change the belt - definitely the cheapest option for starters!

Well I borrowed an alternator from a local breakers and fitted that today,an easier job than I expected but voltage drops straight away again. I put a meter across the battery and neither alternator shows a charge increase so I'm either unlucky and have two duff alternators or could it be the cable at the back of the alternator? Which cable is this that may be a problem? If anyone is looking to remove their alternator it's probably one of the easiest jobs I've had to do. I found when you remove the long bolt with the pulley wheel on it,drive that side of the alternator down and lever the other side up,after removing the short bolt obviously.This puts the alternator in an easy position to pull out.When replacing,the boss with the short bolt, the engine mount,has a split bush in it,tap this out slightly towards the rear of the car.I then filed a few thou off the inner faces of the alternator mount bosses,when putting the alternator back in it slid back into position a lot easier,no hammering required.Anyway I haven't solved the issue but I've now attained Formula One pit standards of alternator removal,so not a complete waste of time.

To rule out the cable, measure the output of the alternator when the engine is running by trying to get the positive from the multimeter round the back of the alternator to touch the nut where the power cable is attached to. Obviously be careful for moving parts.

Thanks Minny,tomorrows job sorted.

To update re my original strange alternator problem, after changing the power steering pump and then refurbishing the alternator, the dry bearing noise was still present. I then changed the 11 month old original Porsche drive belt and the noise disappeared along with the low voltage when the car had been in the rain or washed. Now after 1 month, the low voltage after the rain or washing the car has returned. It turns out the belt is slipping when wet and after a minute or so of the engine running it grips again. The belt is in as new a condition with no evidence of glazing. There are no oil leaks near or around the belt. Anyone has any clues why this has happened again? Rare as it is, could it be the drive belt tensioner that is not applying as much a tension as it should? When I changed the belt, I had also cleaned all the pulleys with brake cleaner.

Does anyone have instructions/guidance regarding replacement of the drive belt tensioner? I am hoping the housing it is attached to doesn't have to come out.

You have mail, Min!

I've had the belt changed. I'll let you know after it rains next if that has fixed the issue. Fingers crossed.

Keep us posted as my problems stopped after changing the belt but then started again after about 4 weeks. The belt is slipping again when wet. I have a new Gates belt and power steering pump pulley in the garage to fit sometime this week. Was going to do it tonight but have you seen the gales outside?

Not slipped again yet, so fingers crossed its fixed.