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Registered User
Join Date: Sep 2011
Posts: 3
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Alternator or voltage regulator?
Hi,
My 1974 911 decided to stop charging its battery. The battery is OK, so I assumed that the problem was either with the voltage regulator or alternator. I pulled the alternator (a Marchal 712 237 02 14V) and verified that the brushes were OK. The next step was to have the alternator bench-tested at an auto electric shop. Unfortunately, so far, I have not found a shop that can or will test the alternator with it out of the car. Does anyone know how I can test the voltage regulator and alternator, to determine which is faulty? Thanks, Greg |
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09-29-2011, 06:02 PM
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Fleabit peanut monkey
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Hi Greg,
Welcome to the forum. The parts stores are not equipped to test alternators that are bracket challenged. What I have experienced is if the voltage regulator is marginal, you will charge the battery sufficiently but the charge voltage will be inconsistent. Varying by a great degree - over a volt. When the V reg is working it charges within a few hundredths of a volt. At first blush, I would say your alternator has failed. There are some really good posts in this forum regarding diagnosis. If you search using the advanced search option (when signed in) you can find some really good information on troubleshooting charging systems. You will need a voltage tester - a multi-meter - to employ the tests. If you got nothing but money (i.e., not married and no kids) buy the $700 - on steroids - alternator from our host and be done with it. If you are on a budget you can buy a rebuilt alternator from your local parts house for under $200. Pelican Parts - Product Information: PEL-ALT95-27 |
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09-29-2011, 06:46 PM
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83 911 Production Cab #10
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Hi Greg
Beleive it or not, photo of the car help diagnosticquing  When doing an Advance Searching, search by Search by Keyword: "Charging Systems" within "Search Title Only" and you'll get about 30 threads. This thread may help: Charging system problem - Experts, help keep Porsche practical! (photo)
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Who Will Live... Will See  83 911 Production Cab #10, Slightly Modified: Unslanted, 3.2, PMO EFI, TECgt, CE 911 CAM Sync / Pulley / Wires, SSI, Dansk Sport 2/2, 17" Euromeister, CKO GT3 Seats, Going SOK Super Charger |
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09-29-2011, 07:55 PM
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09-30-2011, 04:38 AM
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Registered User
Join Date: Feb 2011
Location: Bellevue, Wa
Posts: 2,437
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Yea, cant seem to figure out which one either... maybe some pics of that sweet ride!!
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Ed M 86' Coupe |
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09-30-2011, 05:08 AM
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Registered User
Join Date: Sep 2011
Posts: 3
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Thanks to Bob and everyone else who responded to my question. I finally found a shop that would bench test the alternator. Bob, you were right- the alternator was shot.
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10-01-2011, 10:25 AM
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83 911 Production Cab #10
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Is that mean that now you have time to take pictures of the car and upload them
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Who Will Live... Will See 83 911 Production Cab #10, Slightly Modified: Unslanted, 3.2, PMO EFI, TECgt, CE 911 CAM Sync / Pulley / Wires, SSI, Dansk Sport 2/2, 17" Euromeister, CKO GT3 Seats, Going SOK Super Charger |
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10-01-2011, 02:37 PM
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Registered User
Join Date: Sep 2011
Posts: 3
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I'll take some pictures once it is running again.
I found a book that describes some basic regulator/alternator tests that you can use to determine which component is bad: kb-kbh.dk/shipslib/el_ombord/alternatorhandbook_ocr.pdf |
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10-02-2011, 07:34 AM
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Fleabit peanut monkey
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Greg,
Thanks for the pdf post. Somebody put some time into that bad boy to build it. Lots of hand diagrams. Nice. JJ 911Sc's link is great. See the Grady Clay info. |
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10-04-2011, 05:13 PM
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1981 Porsche 911 SC Targa
Das Babe
Das Babe Metalberiech
1974 911 Coupe
