 To be double sure of bad alternator |
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| stoneman30hotmail |
 Sep 21 2023, 05:58 PM
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Member  Group: Members Posts: 80 Joined: 10-September 22 From: Greensboro, NC Member No.: 26,834 Region Association: South East States  |
I read some threads and "how to test alternator regulator". But they're pretty rudamentary. I don't get 13.5 V at the battery, it just stays at almost 12V. So I gather that usually means alternator. I do see 13.5V at the D+ pin and 3-4 at the DF pin. Does that mean the regulator is trying to work? I thought the 13.5 V meant that the alternator was putting 13.5 somewhere. I tried to short these to "full field" the alternator and fried a small wire without change at the battery. The regulator looks original and I would of course rather change that.
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| Spoke |
Sep 21 2023, 06:26 PM
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Jerry Group: Members Posts: 7,158 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None 
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You can try removing the VR and shorting D+ to DF then starting the car. This will cause the alternator to put out maximum voltage. See what you get at the battery. The battery voltage during this test should be north of 15V.
BTW, is the GEN light on during normal operation of your 914? |
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| stoneman30hotmail |
Sep 22 2023, 11:01 AM
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Member Group: Members Posts: 80 Joined: 10-September 22 From: Greensboro, NC Member No.: 26,834 Region Association: South East States |
QUOTE(Spoke @ Sep 21 2023, 08:26 PM)  You can try removing the VR and shorting D+ to DF then starting the car. This will cause the alternator to put out maximum voltage. See what you get at the battery. The battery voltage during this test should be north of 15V. BTW, is the GEN light on during normal operation of your 914? 17V with that test. So regulator! The trick was taking off the old regulator I guess. Tryinng to short while running didn't work. (IMG:style_emoticons/default/beer.gif) |
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| Spoke |
Sep 22 2023, 11:07 AM
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Jerry Group: Members Posts: 7,158 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None
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QUOTE(stoneman30hotmail @ Sep 22 2023, 01:01 PM) QUOTE(Spoke @ Sep 21 2023, 08:26 PM) You can try removing the VR and shorting D+ to DF then starting the car. This will cause the alternator to put out maximum voltage. See what you get at the battery. The battery voltage during this test should be north of 15V. BTW, is the GEN light on during normal operation of your 914? 17V with that test. So regulator! The trick was taking off the old regulator I guess. Tryinng to short while running didn't work. (IMG:style_emoticons/default/beer.gif) Seems to point to the VR. For sure it's easier to swap a VR versus the alternator.... |
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| stoneman30hotmail |
Oct 9 2023, 08:45 AM
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Member Group: Members Posts: 80 Joined: 10-September 22 From: Greensboro, NC Member No.: 26,834 Region Association: South East States |
QUOTE(Spoke @ Sep 22 2023, 01:07 PM) QUOTE(stoneman30hotmail @ Sep 22 2023, 01:01 PM) QUOTE(Spoke @ Sep 21 2023, 08:26 PM) You can try removing the VR and shorting D+ to DF then starting the car. This will cause the alternator to put out maximum voltage. See what you get at the battery. The battery voltage during this test should be north of 15V. BTW, is the GEN light on during normal operation of your 914? 17V with that test. So regulator! The trick was taking off the old regulator I guess. Tryinng to short while running didn't work. (IMG:style_emoticons/default/beer.gif) Seems to point to the VR. For sure it's easier to swap a VR versus the alternator.... I'm not so sure now. While running I get a nice 13-14V at the battery. But the gen light is still on as there is 17 V at D+. So I'm expecting the alternator to quit. |
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| GregAmy |
Oct 9 2023, 08:53 AM
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#6
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Advanced Member Group: Members Posts: 2,490 Joined: 22-February 13 From: Middletown CT Member No.: 15,565 Region Association: North East States
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QUOTE(stoneman30hotmail @ Oct 9 2023, 09:45 AM) I'm not so sure now. While running I get a nice 13-14V at the battery.. So the alternator is putting out... QUOTE ...But the gen light is still on as there is 17 V at D+. Bad diode in the alternator. That 3-4V differential is enough to turn on the GEN light. Looks like an alternator swap is in your future...sigh... On the plus side...the D+ 17V is only connected to the GEN light. So if you're willing to tolerate that light for a while (or willing to disconnect and tape off the wire) then it is not hurting anything and you can change the altie at your leisure. I drove mine like that for some weeks while I got the part (had a core rebuilt by a crusty old dude in NH for $125, killer workmanship) and worked up the motivation for the fidgety job (a friend on top while you're working the bottom helps). - GA |
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Posts in this topic
stoneman30hotmail To be double sure of bad alternator Sep 21 2023, 05:58 PM
stoneman30hotmail
You can try removing the VR and shorting D+ to DF... Sep 21 2023, 06:51 PM
ClayPerrine
(or willing to disconnect and tape off the wire)
... Oct 9 2023, 01:39 PM GregAmy That is going to shut down the alternator complete... Oct 9 2023, 01:45 PM L-Jet914 If you can find someone with an old VAT40 or a MT3... Sep 21 2023, 11:24 PM |
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