Erratic Voltage ?

Mike Miller · 09-09-2004, 03:22 PM

High guys,
Its been a while sense my last post. I just went through a lot of scambling to get my 89 911 to pass its inspection in TX.

Thankfully this forum exsist to help many diy guys. Had I read enough here I could have helped the guys working to fix my problem. Long story and not enough time tell tonight. However my voltage seems to be a prob. My lights get brighter and my A/C fan blows harder. In TX I don't mind the A/C blowing harder but, I'm afraid it might damage somthing. I plugged in a volt meter in the cigarette and at low rpms it reads 12-13 volts as I drive down the highway it reads between 16-18 volts. This can't be good. Might it be the brushes or the regulator. I have not pulled the alternator yet. Just asking for wisdom before I get into it.

Mike Miller
89 911
120.000 miles

filou · 09-09-2004, 03:59 PM

It sounds like the Voltage regulator is acting up. Correct me if i wrong but i believe yours is internal (part of alternator).
Good luck.
Filou.

jazzbass · 09-09-2004, 04:16 PM

Like filou said - very good change (like 95%) its your voltage regulator. I had the exact same problem. I'll bet your seat belt warning light comes on, too.

The regulator is on the back of your alternator. Pull it out, remove the regulator, install new one, done. 2 hour job for me the first time. If you like to swear, you'll find it comes in handy getting the alternator out of the housing.

Por_sha911 · Por_sha911's Garage

VR is the problem and you want to fix it before you start burning up electrical things. Over charging can also fry a battery (can you say "battery acid boiling over"?)

Mike Miller · 09-09-2004, 07:35 PM

Thanks Chris,

Is that a for sure that the regulator is on the back? Can any one confirm that? Or is there a way to tell? Is that over voltage at 16- 18 to much for the wires and something should be done promptly?

Thanks for the advice,
Mike

Mike Miller · 09-09-2004, 07:36 PM

Thanks Joe,
You posted just as I did.

jazzbass · 09-09-2004, 08:38 PM

Yeah, I'm sure its on the back. I had this same problem and fixed it. Remove the alternator/fan from the housing. The VR is on the back of the alternator.

RoninLB · 09-09-2004, 09:05 PM

only changing the internal voltage regulator with worn alt slip rings is a "maybe" fix. ie: a decent chance the electrics will go bizerk.. but probably not be damaged.. High volts on a DME can get expensive fast.

jazzbass · 09-09-2004, 09:41 PM

Ron - you talking about the brushes that contact the slip rings? These are replaced with the VR on the alternators on Carreras. My new VR has been in for over a year and no bizerk electrics - and I have a volt gauge permantly mounted to watch the voltage.

I'm curious - what is suceptable to damage in the DME from 17-20V? The micro and other logic is part of the 5V system, so it must be regulated (7805 or the like), which should hide these low-level voltage spikes from the MCU. The other stuff is analog drivers and such, which I wouldn't think would be damaged by 20V.

RoninLB · 09-09-2004, 09:59 PM

Quote:

Originally posted by jazzbass
My new VR has been in for over a year and no bizerk electrics -

I'm curious - what is suceptable to damage in the DME from 17-20V?

New brushes may not "fit" worn slip rings. You can run your fingernail over 40k mi slip rings a feel a noticable amt of wear. so the brushes won't be making full contact.

I don't have a DME so I can't be specific on the indivudal parts that toast.. also a CD box, headlights, maybe dash non fused light circuit fire, etc.

it's interesting to note that many circuits of our cars are maxed out with small wires. Although 2 batteries in series will sometimes/depends on prob, spin a bad starter like a gyro.

dillinger · 03:56 AM

If your going thru all the trouble to replace the VR, why not just replace your whole alternator? I bought a remanufactured Bosch for my '83 locally for $224. Go to www.boschusa.com follow the links to select a vehicle, product etc. I just did and you have several choices. Reman 115amp Bosch #AL176X. New 90amp #AL401N, Reman 90amp AL401X. Call your local Autozone, or import autoparts place w/ those numbers and I bet you'll find a good price. Here in Va, I bought mine from BAPGEON, it was a AL400X. BTW, I purchase 90% of my parts from our host, I just wanted a less expensive solution this time.

Don

djmcmath · 09-10-2004, 05:50 AM

Hang on, let's go back to this "bad slip rings" problem. The VR that I ordered from Pelican didn't have replacement slip rings. Are they replaceable without replacing the whole alternator ($224, ouch!)? Can I clean them and place them back into service, as it ought to be the brushes that take the wear, not the rings?

TIA,

Dan

Mike Miller · 09-14-2004, 01:59 AM

I purchesed a new VR. When I removed the old one it looked like one of the brushes was worn pretty good. The slip rings I was not sure about. I took the Alt. to a local shop and he said they looked good. I reinstalled the new VR and put everything back together. It all works great and does a great job of holding voltage steady. Thank for all the help. This is the best place to seek help. In most cases its better than many of the Porsche repair places.

Mike Miller
89 911

RoninLB · 09-14-2004, 02:52 AM

Quote:

Originally posted by Mike Miller
I reinstalled the new VR and put everything back together. It all works great and does a great job of holding voltage steady.

that's great.. thanks for the up-date

Joeaksa · 09-14-2004, 05:02 AM

Mike,

Had the same problem on my 85 model when I lived in Dallas. Could not understand why the lights kept flickering. Put a volt meter on it and the lights were not flickering, they were going "bright then dim" when the alternator/regulator went from 14.5 to 16 volts and the lights were doing their best to keep from exploding.

Found a nice shop in Carrolton who overhauled the alternator and put a new regulator in for under $75. Worked fine the last several years... Have had a digital volt meter installed in the cockpit car ever since.

JoeA

RoninLB · 09-14-2004, 06:50 AM

Quote:

Originally posted by Joeaksa

... Have had a digital volt meter installed in the cockpit

ditto.. a most excellent up-grade..
although I have less eyeball trouble with an analog when quickly scanning gauges.

Joeaksa · 09-14-2004, 10:33 AM

Ron,

We all do after the age of 42-44 years old! I could not get by without the gauge now and its being digital, it tells me when things are not correct by even a tenth of a volt and I start looking for the problem early on.

Joe

Mike Miller · 09-14-2004, 04:47 PM

Joe,
Nice to hear from you. I took a break for a while. Various items keeping me busy.
Mike

WydRyd · 09-14-2004, 05:05 PM

All, be very careful with prolonged driving with an overcharging Alternator/VR. It could potentially blow up your DME ECU or Injector Driver internally (happens to be a proprietary part you can't get!).

Could result in a very expensive repair bill

Joeaksa · 09-14-2004, 05:45 PM

Mike,

Good to hear you are alive and kicking as well. Been busy as a one armed paper hanger myself.

Hows the A/C system working? Bet the fan was blowing very fast for a while! I was very worried about what Merv mentioned as 16+ volts cannot be good for the DME computer but drove for 2.5 years after having the problem with no issue.

JoeA